IPTV ( Internet Based Television )

We know the power of Internet protocol suit as it takes on the world of telecom . Alreday half of Communication has been transferred from legacy telecom signalling protocols like SS7 to IP based communication ( Skype , Hangouts , whatsapp , facebook call ) . The TV service providers too are largely investing in IP based systems like SIP and IMS to deliver their content over Telecom’s IP based network ( Packet switched ).

A consumer today wants HD media content anytime anywhere . The traditional TV solutions just dont match upto the expectations anymore . The IPTV provider in todays time must make investments to deliver content that is media-aware, and device-aware. Not only this it should be  personal, social, and interactive . after all its all about user  experience.

Few popular applications for IPTV solutions developers are

  • Menu overlay with detailed description of channels , categories , programs , movies
  • Replay option also referred to as timeshift . It allows a user to pause , resume and  record the show in his absence and view it later
  • Video on demand which concerns paying and viewing music albums , movies etc on demand
  • Live streaming of events such as president speech , tennis match etc .

Application that can be build around the IPTV context

  • Record and Playback content
  • Information overlay on streaming content
  • Social networking services integrated with IPTV content
  • Parental Control to realtime view , monitor and control what your child is watching on the IPTV
  • Watch the surveillance  footage from IP cameras anywhere
  • Real time communication on IPTV  with advanced features like call continuity , content sync .

Telephony Solutions with Kamailio

Kamailio™ (former OpenSER) is an Open Source SIP Server released under GPL.

Kamailio primarily acts as a SIP server for VOIP and telecommunications platforms under various roles and can handle load of hight CPS ( Calls per second ) with custom call routing logic with the help of scripts .

Rich features set suiting to telephony domain that includes IMS extensions for VoLTE; ENUM; DID and least cost routing; load balancing; routing fail-over; Json and XMLRPC control interface, SNMP monitoring.

To integrate with a carrier grade telecom network as SBC / gateway / inbound/outbound proxy , it can act as IPv4-IPv6 gateway , UDP/TCP/SCTP/WS translator and even had NAT and anti DOS attack support .

If Kamailio is the central to the VoIP system it can also perform accounting with rich database extensions Mysql PostgreSQL UnixODBC Berkeley DB Oracle Redis, MongoDB Cassandra etc

  • Kamailio is SIP (RFC3261) compliant

It can work as Registrar or Location server. For SIP call logic it can become a Proxy or SIP Application server. Can also act like a Redirect , Dispatcher or simply a SIP over websocket server.

  • Kamailio is Customisable to suit business requirement and scale .

It can be embedded to devices as the binary file is small size. Additional modules can be appended for more functions with the same core.

Due to its modular architecture – core, internal libraries , module interface and ability to extend functionality with scripts such as LUA , Kamailio can be readily integrated to a VOIP ecosystem.

  • Call routing and control with Scripting and programming

Offers stateless and transactional stateful SIP Proxy processing ( suited for inbound gateways ) and serial and parallel forking.

Also NAT traversal support for SIP and RTP traffic ( suited to be WebRTC server )

Among other features it offers load balancing with many distribution algorithms and failover support , flexible least cost routing , routing failover and replication for High Availability (HA).

Can be readily integrated with external databases , caches, notification system ( SNS , APNS , GCM ), voip monitors , CDR processors, API systems etc for  efficient call processing.

  • Transport Layers supported 

    • UDP, TCP, TLS and SCTP
    • IPv4 and IPv6
    • gateways via (IPv4 to IPv6, UDP to TLS, a.s.o.)
    • SCTP multi-homing and multi-streaming
    • WebSocket for WebRTC 
  • Asynchronous TCP, UDP and SCTP,

asynchronous SIP message processing and  inter-process message queues communication system

  • Secure Communication ( TLS  + AAA)

    • Digest SIP User authentication
    • Authorization via ACL or group membership
    • IP and Network authentication
    • TLS support for SIP signaling
    • transparent handling of SRTP for secure audio
    • TLS domain name extension support
    • authentication and authorization against database (MySQL, PostgreSQL, UnixODBC, BerkeleyDB, Oracle, text files), RADIUS and DIAMETER
  • IP and DNS

    • support for SRV and NAPTR DNS lookups
    • SRV DNS failover
    • DNSsec support
    • ENUM support
    • internal DNS caching system – avoid DNS blocking
    • IP level Blacklists
    • multi-homed and multi-domain support
    • topology hiding – hide IP addresses in SIP headers to protect your network architecture
  • Accounting

Kamailio gives event based and configurable accounting data details. Can show multi-leg call accounting ( A leg to B leg ). It can store to database, Radius or Diameter based on module used . Has a prepaid engine.

  • External Interaction

text-based management interface via FIFO file, udp, xmlrpc and unix sockets.

RPC control interface – via XMLRPC, UDP or TCP

  • Rich Communication Services (RCS)

    • SIP SIMPLE Presence Server (rich presence)
    • Presence User Agent ( SUBSCRIBE , NOTIFY and PUBLSH)
    • XCAP client capabilities and Embedded XCAP Server
    • Presence DialogInfo support – SLA/BLA
    • Instant Messaging ( IM) 
    • Embedded MSRP relay
  • Monitoring and Troubleshooting

Support for SNMP – interface to Simple Network Management Protocol.  For Debugging it has config debugger , remote control via XMLRPC and error message logging system .Provides internal statistics exported via RPC and SNMP.

  • Extensibility APIs

The supported  one are Perl  , Java SIP Servlet Application Interface  , Lua  , Managed Code (C#) , Python

  • Multiple Database Backends

(MySQL, PostgreSQL, SQLite, UnixODBC, BerkeleyDB, Oracle, text files) and other database types which have unixodbc drivers. ‘

It can have connections pool and different backends  be used at same time (e.g., accounting to Oracle and authorization against MySQL).

Has connectors for Memcached, Redis , MongoDB and Cassandra no-SQL backends

  • Interconnectivity

Acts as SIP to PSTN gateway and gateway to sms or xmpp and other IM services. Has Interoperability with SIP enabled devices and applications such as SIP phones (Snom, Cisco, etc.), Media Servers (Asterisk, FreeSwitch, etc.)

  • IMS

    • diameter support and authentication
    • I-CSCF, P-CSCF, S-CSCF
    • charging, QOS, ISC
  • Miscellaneous

    • CPL – Call Processing Language (RFC3880)
    • Internal generic caching system
    • Memcached connector
    • Redis NoSQL database connector
    • CLI – kamctl and sercmd
    • Web Management Interface: Siremis
    • SIP-T and SIP-I
    • music on hold queue
    • message body compression/decompression (gzip-deflate)
  • Extensive documentation for both administrators and developers

Scalability:

  • Kamailio can run on embedded systems, with limited resources – the performances can be up to hundreds of call setups per second
  • used as load balancer in stateless mode, Kamailio can handle over 5000 call setups per second
  • on systems with 4GB memory, Kamailio can serve a population over 300 000 online subscribers
  • system can easily scale by adding more Kamailio servers
  • Kamailio can be used in geographic distributed VoIP platforms
  • Kamailio least-cost-routing scales up to millions of routing rules
  • straightforward failover and redundancy

Start Kamalio

service kamailo start

Logs

tail -f /var/log/kamailio

To Check if Kamailio instance is running

>ps -ax | grep “kamailio”

57411 ?        S      0:01 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 4096 -M 128 -u root -g root

Installation and Configuration

Installing kamailio from git repo

clone kamailio from their github https://github.com/kamailio/kamailio

goto desired branch

The contents of clonned folder are

COPYING ChangeLog INSTALL ISSUES Makefile README README.md doc etc misc pkg test utils

run ‘make cfg’ which compiles using gcc abd created ‘src’ folder with contents

make cfg

Makefile Makefile.defs Makefile.groups Makefile.modules Makefile.rules Makefile.sources Makefile.utils core main.c modules.lst Makefile.cfg Makefile.dirs Makefile.libs Makefile.radius Makefile.shared Makefile.targets config.mak lib modules

Edit modules.lst to enable db_mysql and dialplan module

vim src/modules.lst

//the list of extra modules to compile
include_modules= db_mysql

Use ‘make’ command followed by make all . Make sure to have gcc bison and flex installed

make cfg
make all

Alternativey on debian system , use readymade measures like

apt install mysql-server
apt install kamailio kamailio-mysql-modules

To validate and verify the location of kamillio use ‘which kamailio’ which returns /usr/sbin/kamailio

For Modules installation , check all avaible modules with command ‘apt search kamailio’and to install a new module such as websockt module use ‘apt install kamailio-websocket-modules’

Database access
After installaing kamailio , edit the kamailio.cfg file in /etc/kamailio to set the reachabe SIP domain, database engine, username/password etc to connect to databaseand enable the kamdbctl script to run and create users and tables, etc.

SIP_DOMAIN=kamailio.org

SIP_DOMAIN=17.3.4.5

chrooted directory

$CHROOT_DIR=”/path/to/chrooted/directory”

database type: MYSQL, PGSQL, ORACLE, DB_BERKELEY, DBTEXT, or SQLITE by default none is loaded

DBENGINE=MYSQL

Run kamdbctl to create users and database now

kamdbctl create

the database created is name kamailio and its tables are

+---------------------+
 | Tables_in_kamailio  |
 +---------------------+
 | acc                 |
 | acc_cdrs            |
 | active_watchers     |
 | address             |
 | aliases             |
 | carrier_name        |
 | carrierfailureroute |
 | carrierroute        |
 | cpl                 |
 | dbaliases           |
 | dialog              |
 | dialog_vars         |
 | dialplan            |
 | dispatcher          |
 | domain              |
 | domain_attrs        |
 | domain_name         |
 | domainpolicy        |
 | globalblacklist     |
 | grp                 |
 | htable              |
 | imc_members         |
 | imc_rooms           |
 | lcr_gw              |
 | lcr_rule            |
 | lcr_rule_target     |
 | location            |
 | location_attrs      |
 | missed_calls        |
 | mohqcalls           |
 | mohqueues           |
 | mtree               |
 | mtrees              |
 | pdt                 |
 | pl_pipes            |
 | presentity          |
 | pua                 |
 | purplemap           |
 | re_grp              |
 | rls_presentity      |
 | rls_watchers        |
 | rtpproxy            |
 | sca_subscriptions   |
 | silo                |
 | sip_trace           |
 | speed_dial          |
 | subscriber          |
 | trusted             |
 | uacreg              |
 | uid_credentials     |
 | uid_domain          |
 | uid_domain_attrs    |
 | uid_global_attrs    |
 | uid_uri             |
 | uid_uri_attrs       |
 | uid_user_attrs      |
 | uri                 |
 | userblacklist       |
 | usr_preferences     |
 | version             |
 | watchers            |
 | xcap                |
 +---------------------+

Kamctlrc

The Kamailio configuration file for the control tools. Can set variables used in the kamctl and kamdbctl setup scripts. Per default all variables here are commented out, the control tools will use their internal default values. This file lets to edit  SIP domain, the database engine, username/password/ to connect to database, etc.

## your SIP domain
 SIP_DOMAIN=13.126.169.58
## chrooted directory
# $CHROOT_DIR="/path/to/chrooted/directory"
## database type: MYSQL, PGSQL, ORACLE, DB_BERKELEY, DBTEXT, or SQLITE
# by default none is loaded

# If you want to setup a database with kamdbctl, you must at least specify this parameter.

 DBENGINE=MYSQL
## database host
# DBHOST=localhost
## database host
# DBPORT=3306
## database name (for ORACLE this is TNS name)
# DBNAME=kamailio
# database path used by dbtext, db_berkeley or sqlite
# DB_PATH="/usr/local/etc/kamailio/dbtext"
database read/write user
# DBRWUSER="kamailio"
## password for database read/write user
# DBRWPW="kamailiorw"

database read only user

# DBROUSER="kamailioro"
## password for database read only user
# DBROPW="kamailioro"
## database access host (from where is kamctl used)
# DBACCESSHOST=192.168.0.1

database super user (for ORACLE this is ‘scheme-creator’ user)

# DBROOTUSER="root"
## password for database super user
## - important: this is insecure, targeting the use only for automatic testing
## - known to work for: mysql
# DBROOTPW="dbrootpw"
## database character set (used by MySQL when creating database)
#CHARSET="latin1"
## user name column
# USERCOL="username"
# SQL definitions

# If you change this definitions here, then you must change them
# in db/schema/entities.xml too.
# FIXME
# FOREVER="2030-05-28 21:32:15"
# DEFAULT_Q="1.0"
# Program to calculate a message-digest fingerprint
# MD5="md5sum"
# awk tool
# AWK="awk"
# gdb tool
# GDB="gdb"

# If you use a system with a grep and egrep that is not 100% gnu grep compatible,
# e.g. solaris, install the gnu grep (ggrep) and specify this below.

grep tool
# GREP="grep"
# egrep tool
# EGREP="egrep"
# sed tool
# SED="sed"
# tail tool
# LAST_LINE="tail -n 1"
# expr tool
# EXPR="expr"

Describe what additional tables to install. Valid values for the variables below are yes/no/ask. With ask (default) it will interactively ask the user for an answer, while yes/no allow for automated, unassisted installs.

#If to install tables for the modules in the EXTRA_MODULES variable.

# INSTALL_EXTRA_TABLES=ask
# If to install presence related tables.
# INSTALL_PRESENCE_TABLES=ask
# If to install uid modules related tables.
# INSTALL_DBUID_TABLES=ask

 Define what module tables should be installed.

If you use the postgres database and want to change the installed tables, then you must also adjust the STANDARD_TABLES or EXTRA_TABLES variable accordingly in the kamdbctl.base script.

standard modules

# STANDARD_MODULES="
standard acc lcr domain group permissions registrar usrloc msilo
alias_db uri_db speeddial avpops auth_db pdt dialog dispatcher
dialplan"

extra modules

# EXTRA_MODULES="
imc cpl siptrace domainpolicy carrierroute userblacklist htable purple sca"
 type of aliases used: DB - database aliases; UL - usrloc aliases
- default: none , ALIASES_TYPE="DB"
control engine: RPCFIFO
 - default RPCFIFO
 CTLENGINE="RPCFIFO"

## path to FIFO file for engine RPCFIFO
# RPCFIFOPATH="/var/run/kamailio/kamailio_rpc_fifo"

## check ACL names; default on (1); off (0)
# VERIFY_ACL=1

## ACL names - if VERIFY_ACL is set, only the ACL names from below list are accepted
# ACL_GROUPS="local ld int voicemail free-pstn"

## check if user exists (used by some commands such as acl);
## - default on (1); off (0)

# VERIFY_USER=1

## verbose - debug purposes - default '0'
# VERBOSE=1

## do (1) or don't (0) store plaintext passwords
## in the subscriber table - default '1'

# STORE_PLAINTEXT_PW=0

Kamailio START Options

PID file path – default is: /var/run/kamailio/kamailio.pid

# PID_FILE=/var/run/kamailio/kamailio.pid

Extra start options – default is: not set

# example: start Kamailio with 64MB share memory: STARTOPTIONS="-m 64"
# STARTOPTIONS=

Kamailio.cfg

config files are used to customize and deploy SIP services since each and every SIP packet is route based on policies specified in conf file ( routing blocks ). Location when installed from source – /usr/local/etc/kamailio/kamailio.cfg , when installed from package – /etc/kamailio/kamailio.cfg

The features in config file :-

  • User authentication

Kamailio doesn’t have user authentication by default , so to enable it one must

#!define WITH_MYSQL
#!define WITH_AUTH

kamdbctl tool is to be used for creating and managing the database.

kamdbctl create

Kamctl is used for adding subscriber information and password.

kamctl add altanai1 123
mysql: [Warning] Using a password on the command line interface can be insecure.
MySQL password for user 'kamailio@localhost': 
mysql: [Warning] Using a password on the command line interface can be insecure.
new user 'altanai1' added

More details in Tools section below .

  • IP authorization
  • accounting
  • registrar and location servicesTo have persisant location enabled so that records are not lost once kamailio are restarted , we need to save it to database and reload when restarting
#!define WITH_USRLOCDB
  • attacks detection and blocking (anti-flood protection)
  • NAT traversal

requires RTP proxy for RTP relay . NAT traversal support can be set by

#!define WITH_NAT
  • short dialing on server
  • multiple identities (aliases) for subscribers
  • multi-domain support
  • routing to a PSTN gateway
  • routing to a voicemail server
  • TLS encryption
  • instant messaging (pager mode with MESSAGE requests)
  • presence services

Kamailio (OpenSER) SIP Server v4.3- default configuration script

Several features can be enabled using ‘#!define WITH_FEATURE’ directives:

To run in debug mode: define WITH_DEBUG

To enable mysql: define WITH_MYSQL

To enable authentication execute: enable mysql and  define WITH_AUTH

To enable IP authentication execute: enable mysql ,  enable authentication ,  define WITH_IPAUTH and  add IP addresses with group id ‘1’ to ‘address’ table

To enable persistent user location execute:


enable mysql

define WITH_USRLOCDB

To enable presence server execute:


enable mysql

define WITH_PRESENCE

To enable nat traversal execute:

define WITH_NAT

Install RTPProxy: http://www.rtpproxy.org

start RTPProxy:

rtpproxy -l your_public_ip -s udp:localhost:7722

option for NAT SIP OPTIONS keepalives: WITH_NATSIPPING

To enable PSTN gateway routing execute:

define WITH_PSTN

set the value of pstn.gw_ip

check route[PSTN] for regexp routing condition

To enable database aliases lookup execute:


enable mysql

define WITH_ALIASDB

To enable speed dial lookup execute:


enable mysql

define WITH_SPEEDDIAL

To enable multi-domain support execute:


enable mysql

define WITH_MULTIDOMAIN

To enable TLS support execute:


adjust CFGDIR/tls.cfg as needed

define WITH_TLS

To enable XMLRPC support execute:


define WITH_XMLRPC

adjust route[XMLRPC] for access policy

To enable anti-flood detection execute:

adjust pike and htable=>ipban settings as needed (default is block if more than 16 requests in 2 seconds and ban for 300 seconds)

define WITH_ANTIFLOOD

To block 3XX redirect replies execute:

define WITH_BLOCK3XX

To enable VoiceMail routing execute:

define WITH_VOICEMAIL

set the value of voicemail.srv_ip

adjust the value of voicemail.srv_port

To enhance accounting execute:


enable mysql

define WITH_ACCDB

add following columns to database


define WITH_MYSQL

define WITH_AUTH

define WITH_USRLOCDB

#!ifdef ACCDB_COMMENT

ALTER TABLE acc ADD COLUMN src_user VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE acc ADD COLUMN src_domain VARCHAR(128) NOT NULL DEFAULT '';

ALTER TABLE acc ADD COLUMN src_ip varchar(64) NOT NULL default '';

ALTER TABLE acc ADD COLUMN dst_ouser VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE acc ADD COLUMN dst_user VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE acc ADD COLUMN dst_domain VARCHAR(128) NOT NULL DEFAULT '';

ALTER TABLE missed_calls ADD COLUMN src_user VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE missed_calls ADD COLUMN src_domain VARCHAR(128) NOT NULL DEFAULT '';

ALTER TABLE missed_calls ADD COLUMN src_ip varchar(64) NOT NULL default '';

ALTER TABLE missed_calls ADD COLUMN dst_ouser VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE missed_calls ADD COLUMN dst_user VARCHAR(64) NOT NULL DEFAULT '';

ALTER TABLE missed_calls ADD COLUMN dst_domain VARCHAR(128) NOT NULL DEFAULT '';

#!endif

Include Local Config If Exists

import_file “kamailio-local.cfg”

Value defines – IDs used later in config #!ifdef WITH_MYSQL # – database URL – used to connect to database server by modules such # as: auth_db, acc, usrloc, a.s.o.

  
 #!ifndef DBURL 
 #!define DBURL "mysql://kamailio:kamailiorw@localhost/kamailio" 
  #!define DBURL "mysql://kamailio:kamailiorw@localhost/kamailio" 
# !endif

 #!ifdef WITH_MULTIDOMAIN# - the value for 'use_domain' paramete
 #!define MULTIDOMAIN 1
 #!else
 #!define MULTIDOMAIN 0
 #!endif

 # FLT_ - per transaction (message) flags 
 # FLB_ - per branch flags
 #!define FLT_ACC 1
 #!define FLT_ACCMISSED 2
 #!define FLT_ACCFAILED 3
 #!define FLT_NATS 5
 #!define FLB_NATB 6
 #!define FLB_NATSIPPING 

 !substdef "!MY_IP_ADDR!!g"
 #!substdef "!MY_DOMAIN!!g" 
 #!substdef "!MY_WS_PORT!8080!g"
 #!substdef "!MY_WSS_PORT!4443!g"
 #!substdef "!MY_WS_ADDR!tcp:MY_IP_ADDR:MY_WS_PORT!g"
 #!substdef "!MY_WSS_ADDR!tls:MY_IP_ADDR:MY_WSS_PORT!g"</pre>
 
 #!define WITH_WEBSOCKETS
 #!ifdef WITH_DEBUG
 debug=4
 log_stderror=yes
 #!else
 debug=2
 log_stderror=no
 #!endif

 memdbg=5
 memlog=5
 log_facility=LOG_LOCAL0
 fork=yes
 children=4
 
disable TCP (default on)
 #disable_tcp=yes
 enable_sctp = 0

disable the auto discovery of local aliases based on reverse DNS on IPs (default on)
 #auto_aliases=no

add local domain aliases
#alias=”sip.mydomain.com”

// port to listen to can be specified more than once if needed to listen on many ports
port=5060
#!ifdef WITH_TLS
enable_tls=yes
#!endif

life time of TCP connection when there is no traffic – a bit higher than registration expires to cope with UA behind NAT

#!ifdef WITH_PSTN
# PSTN GW Routing
# - pstn.gw_ip: valid IP or hostname as string value, example:
# pstn.gw_ip = "10.0.0.101" desc "My PSTN GW Address"
# - by default is empty to avoid misrouting
pstn.gw_ip = "" desc "PSTN GW Address"
pstn.gw_port = "" desc "PSTN GW Port"
#!endif

ifdef WITH_VOICEMAIL
# VoiceMail Routing on offline, busy or no answer
# - by default Voicemail server IP is empty to avoid misrouting
voicemail.srv_ip = "" desc "VoiceMail IP Address"
voicemail.srv_port = "5060" desc "VoiceMail Port"
#!endif

Modules Section

set paths to location of modules (to sources or installation folders)

#!ifdef WITH_SRCPATH
mpath="modules/"
#!else
mpath="/usr/lib/x86_64-linux-gnu/kamailio/modules/"
#!endif

#!ifdef WITH_MYSQL
loadmodule "db_mysql.so"
#!endif

loadmodule "mi_fifo.so"
loadmodule "kex.so"
loadmodule "corex.so"
loadmodule "tm.so"
loadmodule "tmx.so"
loadmodule "sl.so"
loadmodule "rr.so"
loadmodule "pv.so"
loadmodule "maxfwd.so"
loadmodule "usrloc.so"
loadmodule "registrar.so"
loadmodule "textops.so"
loadmodule "siputils.so"
loadmodule "xlog.so"
loadmodule "sanity.so"
loadmodule "ctl.so"
loadmodule "cfg_rpc.so"
loadmodule "mi_rpc.so"
loadmodule "acc.so"

#!ifdef WITH_AUTH
loadmodule "auth.so"
loadmodule "auth_db.so"
#!ifdef WITH_IPAUTH
loadmodule "permissions.so"
#!endif
#!endif

#!ifdef WITH_ALIASDB
loadmodule "alias_db.so"
#!endif

#!ifdef WITH_SPEEDDIAL
loadmodule "speeddial.so"
#!endif

#!ifdef WITH_MULTIDOMAIN
loadmodule "domain.so"
#!endif

#!ifdef WITH_PRESENCE
loadmodule "presence.so"
loadmodule "presence_xml.so"
#!endif

#!ifdef WITH_NAT
loadmodule "nathelper.so"
loadmodule "rtpproxy.so"
#!endif

#!ifdef WITH_TLS
loadmodule "tls.so"
#!endif

#!ifdef WITH_ANTIFLOOD
loadmodule "htable.so"
loadmodule "pike.so"
#!endif

#!ifdef WITH_XMLRPC
loadmodule "xmlrpc.so"
#!endif

#!ifdef WITH_DEBUG
loadmodule "debugger.so"
#!endif

#!ifdef WITH_WEBSOCKETS
loadmodule "xhttp.so"
#loadmodule "websocket.so"
loadmodule "nathelper.so"
#!endif

----- mi_fifo params -----
#modparam("mi_fifo", "fifo_name", "/var/run/kamailio/kamailio_fifo")

----- ctl params -----
#modparam("ctl", "binrpc", "unix:/var/run/kamailio/kamailio_ctl")

----- tm params -----
# auto-discard branches from previous serial forking leg
modparam("tm", "failure_reply_mode", 3)
# default retransmission timeout: 30sec
modparam("tm", "fr_timer", 30000)
# default invite retransmission timeout after 1xx: 120sec
modparam("tm", "fr_inv_timer", 120000)

----- rr params -----
# set next param to 1 to add value to ;lr param (helps with some UAs)
modparam("rr", "enable_full_lr", 0)
# do not append from tag to the RR (no need for this script)
modparam("rr", "append_fromtag", 0)

registrar params


modparam("registrar", "method_filtering", 1)
/* uncomment the next line to disable parallel forking via location */
# modparam("registrar", "append_branches", 0)
/* uncomment the next line not to allow more than 10 contacts per AOR */
#modparam("registrar", "max_contacts", 10)
# max value for expires of registrations
modparam("registrar", "max_expires", 3600)
# set it to 1 to enable GRUU
modparam("registrar", "gruu_enabled", 0)

enhanced DB accounting


#!ifdef WITH_ACCDB

modparam("acc", "db_flag", FLT_ACC)

modparam("acc", "db_missed_flag", FLT_ACCMISSED)

modparam("acc", "db_url", DBURL)

modparam("acc", "db_extra",

"src_user=$fU;src_domain=$fd;src_ip=$si;"

"dst_ouser=$tU;dst_user=$rU;dst_domain=$rd")

#!endif

usrloc params – enable DB persistency for location entries


#!ifdef WITH_USRLOCDB

modparam("usrloc", "db_url", DBURL)

modparam("usrloc", "db_mode", 2)

modparam("usrloc", "use_domain", MULTIDOMAIN)

#!endif

auth_db params


#!ifdef WITH_AUTH

modparam("auth_db", "db_url", DBURL)

modparam("auth_db", "calculate_ha1", yes)

modparam("auth_db", "password_column", "password")

modparam("auth_db", "load_credentials", "")

modparam("auth_db", "use_domain", MULTIDOMAIN)

permissions params


#!ifdef WITH_IPAUTH

modparam("permissions", "db_url", DBURL)

modparam("permissions", "db_mode", 1)

#!endif

#!endif

alias_db params


#!ifdef WITH_ALIASDB

modparam("alias_db", "db_url", DBURL)

modparam("alias_db", "use_domain", MULTIDOMAIN)

#!endif

speeddial params


#!ifdef WITH_SPEEDDIAL

modparam("speeddial", "db_url", DBURL)

modparam("speeddial", "use_domain", MULTIDOMAIN)

#!endif

domain params

#!ifdef WITH_MULTIDOMAIN
modparam("domain", "db_url", DBURL)
modparam("domain", "register_myself", 1)
#!endif
#!ifdef WITH_PRESENCE

presence params

modparam("presence", "db_url", DBURL)

presence_xml params

modparam("presence_xml", "db_url", DBURL)
modparam("presence_xml", "force_active", 1)

WITH_NAT

rtpproxy params
modparam("rtpproxy", "rtpproxy_sock", "udp:127.0.0.1:7722")

nathelper params

 modparam("nathelper", "natping_interval", 30)
 modparam("nathelper", "ping_nated_only", 1)
 modparam("nathelper", "sipping_bflag", FLB_NATSIPPING)
 modparam("nathelper", "sipping_from", "sip:pinger@kamailio.org") 

params needed for NAT traversal in other modules

modparam("nathelper|registrar", "received_avp", "$avp(RECEIVED)")
modparam("usrloc", "nat_bflag", FLB_NATB)

tls params

#!ifdef WITH_TLS

modparam("tls", "config", "/etc/kamailio/tls.cfg")

#!endif

pike params

#!ifdef WITH_ANTIFLOOD

modparam("pike", "sampling_time_unit", 2)
modparam("pike", "reqs_density_per_unit", 16)
modparam("pike", "remove_latency", 4)

htable params

ip ban htable with autoexpire after 5 minutes

modparam("htable", "htable", "ipban=>size=8;autoexpire=300;")

#!endif

xmlrpc params

modparam("xmlrpc", "route", "XMLRPC");
modparam("xmlrpc", "url_match", "^/RPC")

debugger params

#!ifdef WITH_DEBUGs
modparam("debugger", "cfgtrace", 1)
#!endif

nathelper params

#!ifdef WITH_WEBSOCKETS
modparam("nathelper|registrar", "received_avp", "$avp(RECEIVED)")
#!endif

Note: leaving NAT pings turned off here as nathelper is <em>only</em> being used for&nbsp;WebSocket connections. NAT pings are not needed as WebSockets have&nbsp;their own keep-alives.

Routing Logic

Main SIP request routing logic processing of any incoming SIP request starts with this route

request_route { 
# per request initial checks 
route(REQINIT);
 #!ifdef WITH_WEBSOCKETS 
    if (nat_uac_test(64)) {     
        force_rport();     
        if (is_method("REGISTER")) {          
            fix_nated_register();     
        } else {         
            fix_nated_contact();         
            if (!add_contact_alias()) {  
                   xlog("L_ERR", "Error aliasing contact \n");             
                   sl_send_reply("400", "Bad Request");                    exit;         }     } } 
#!endif 
# NAT detection 
route(NATDETECT); 
# CANCEL processing 
if (is_method("CANCEL")) {     
    if (t_check_trans()) {         
        route(RELAY);     
    }     
exit; 
} 

# handle requests within SIP dialogs 
route(WITHINDLG); 
### only initial requests (no To tag) 
# handle retransmissions 
if(t_precheck_trans()) { 
    t_check_trans(); 
    exit; 
} 
t_check_trans(); 

# authentication 
route(AUTH); 

# record routing for dialog forming requests (in case they are routed) - remove preloaded route headers 
remove_hf("Route"); 

if (is_method("INVITE|SUBSCRIBE")) 
record_route(); 

# account only INVITEs 
if (is_method("INVITE")) {     
    setflag(FLT_ACC); # do accounting 
}
# dispatch requests to foreign domains 
route(SIPOUT); 

### requests for my local domains 
# handle presence related requests 
route(PRESENCE); 

# handle registrations 
route(REGISTRAR); 
if ($rU==$null) {     
# request with no Username in RURI     sl_send_reply("484","Address Incomplete");     
exit; 
} 
# dispatch destinations to PSTN route(PSTN); 

# user location service 
route(LOCATION); }

Wrapper for relaying requests

enable additional event routes for forwarded requests – serial forking, RTP relaying handling, a.s.o.

route[RELAY] {
if (is_method(“INVITE|BYE|SUBSCRIBE|UPDATE”)) {
if(!t_is_set(“branch_route”))
t_on_branch(“MANAGE_BRANCH”);
}
if (is_method(“INVITE|SUBSCRIBE|UPDATE”)) {
if(!t_is_set(“onreply_route”))
t_on_reply(“MANAGE_REPLY”);
}
if (is_method(“INVITE”)) {
if(!t_is_set(“failure_route”))
t_on_failure(“MANAGE_FAILURE”);
}
if (!t_relay()) {
sl_reply_error();
}
exit;
}

Per SIP request initial checks

route[REQINIT] { #!ifdef WITH_ANTIFLOOD # flood detection from same IP and traffic ban for a while # be sure you exclude checking trusted peers, such as pstn gateways – local host excluded (e.g., loop to self) if(src_ip!=myself) { if($sht(ipban=>$si)!=$null) { # ip is already blocked xdbg(“request from blocked IP – $rm from $fu (IP:$si:$sp)\n”); exit; } if (!pike_check_req()) { xlog(“L_ALERT”,”ALERT: pike blocking $rm from $fu (IP:$si:$sp)\n”); $sht(ipban=>$si) = 1; exit; } } if($ua =~ “friendly-scanner”) { sl_send_reply(“200”, “OK”); exit; } #!endif if (!mf_process_maxfwd_header(“10”)) { sl_send_reply(“483″,”Too Many Hops”); exit; } if(is_method(“OPTIONS”) && uri==myself && $rU==$null) { sl_send_reply(“200″,”Keepalive”); exit; } if(!sanity_check(“1511”, “7”)) { xlog(“Malformed SIP message from $si:$sp\n”); exit; } }

Handle requests within SIP dialogs

route[WITHINDLG] {
    if (!has_totag()) return;

    if (has_totag()) {

#sequential request withing a dialog should take the path determined by record-routing

        if (loose_route()) {
            #!ifdef WITH_WEBSOCKETS
            if ($du == "") {
                if (!handle_ruri_alias()) {
                    xlog("L_ERR", "Bad alias <$ru>\n");
                    sl_send_reply("400", "Bad Request");
                    exit;
                }
            }
            #!endif
         }
     exit;
     }

#sequential request within a dialog should  take the path determined by record-routing
    if (loose_route()) {
        route(DLGURI);
        if (is_method("BYE")) {
            setflag(FLT_ACC); # do accounting ...
            setflag(FLT_ACCFAILED); # ... even if the transaction fails
        }
        else if ( is_method("ACK") ) {
            # ACK is forwarded statelessy
            route(NATMANAGE);
        }
        else if ( is_method("NOTIFY") ) {
            # Add Record-Route for in-dialog NOTIFY as per RFC 6665.
            record_route();
        }
        route(RELAY);
        exit;
    }

    if (is_method("SUBSCRIBE") && uri == myself) {
    # in-dialog subscribe requests
        route(PRESENCE);
        exit;
    }

if ( is_method("ACK") ) {
    if ( t_check_trans() ) {
        # no loose-route, but stateful ACK;
        # must be an ACK after a 487
        # or e.g. 404 from upstream server
        route(RELAY);
        exit;
    } else {
        # ACK without matching transaction ... ignore and discard
        exit;
    }
}

sl_send_reply("404","Not here");
exit;
}


Handle SIP registrations





User location service

route[LOCATION] {

#!ifdef WITH_SPEEDDIAL
# search for short dialing - 2-digit extension
if($rU=~"^[0-9][0-9]$")
    if(sd_lookup("speed_dial"))
    route(SIPOUT);
#!endif

#!ifdef WITH_ALIASDB
# search in DB-based aliases
    if(alias_db_lookup("dbaliases"))
    route(SIPOUT);
#!endif

$avp(oexten) = $rU;
if (!lookup("location")) {
    $var(rc) = $rc;
    route(TOVOICEMAIL);
    t_newtran();
    switch ($var(rc)) {
        case -1:
        case -3:
           send_reply("404", "Not Found");
        exit;
        case -2:
           send_reply("405", "Method Not Allowed");
        exit;
    }
}

# when routing via usrloc, log the missed calls also
if (is_method("INVITE")) {
    setflag(FLT_ACCMISSED);
}

route(RELAY);
exit;
}

Presence server processing

route[PRESENCE] {

if(!is_method("PUBLISH|SUBSCRIBE"))
return;

if(is_method("SUBSCRIBE") && $hdr(Event)=="message-summary") {
    route(TOVOICEMAIL);
    # returns here if no voicemail server is configured
    sl_send_reply("404", "No voicemail service");
    exit;
}

#!ifdef WITH_PRESENCE
if (!t_newtran()) {
    sl_reply_error();
    exit;
}

if(is_method("PUBLISH")) {
    handle_publish();
    t_release();
} else if(is_method("SUBSCRIBE")) {
    handle_subscribe();
    t_release();
}
exit;
#!endif

# if presence enabled, this part will not be executed
if (is_method("PUBLISH") || $rU==$null) {
    sl_send_reply("404", "Not here");
    exit;
}
return;
}

IP authorization and user authentication

route[AUTH] {
#!ifdef WITH_AUTH

#!ifdef WITH_IPAUTH
if((!is_method("REGISTER")) && allow_source_address()) {
    # source IP allowed
    return;
}
#!endif

if (is_method("REGISTER") || from_uri==myself)
{
    # authenticate requests
    if (!auth_check("$fd", "subscriber", "1")) {
        auth_challenge("$fd", "0");
        exit;
    }

    # user authenticated - remove auth header
    if(!is_method("REGISTER|PUBLISH"))
        consume_credentials();
    }

# if caller is not local subscriber, then check if it calls
# a local destination, otherwise deny, not an open relay here
    if (from_uri!=myself && uri!=myself) {
        sl_send_reply("403","Not relaying");
        exit;
    }

#!endif
return;
}

Caller NAT detection

route[NATDETECT] {
#!ifdef WITH_NAT
force_rport();

if (nat_uac_test("19")) {
    if (is_method("REGISTER")) {
        fix_nated_register();
    } else {
        if(is_first_hop())
            set_contact_alias();
    }
    setflag(FLT_NATS);
}
#!endif
return;
}

RTPProxy control and signaling updates for NAT traversal

route[NATMANAGE] {

#!ifdef WITH_NAT
if (is_request()) {
    if(has_totag()) {
        if(check_route_param("nat=yes")) {
            setbflag(FLB_NATB);
        }
     }
}
if (!(isflagset(FLT_NATS) || isbflagset(FLB_NATB)))
return;

rtpproxy_manage("co");

if (is_request()) {
    if (!has_totag()) {
        if(t_is_branch_route()) {
            add_rr_param(";nat=yes");
        } 
    }
}

if (is_reply()) {
    if(isbflagset(FLB_NATB)) {
        if(is_first_hop())
        set_contact_alias();
    }
}

#!endif
return;
}

URI update for dialog requests

route[DLGURI] {
#!ifdef WITH_NAT
if(!isdsturiset()) {
    handle_ruri_alias();
}
#!endif
return;
}

Routing to foreign domains

route[SIPOUT] {
if (uri==myself) return;

append_hf("P-hint: outbound\r\n");
route(RELAY);
exit;
}

PSTN GW routing

route[PSTN] {
#!ifdef WITH_PSTN
# check if PSTN GW IP is defined
if (strempty($sel(cfg_get.pstn.gw_ip))) {
xlog("SCRIPT: PSTN routing enabled but pstn.gw_ip not defined\n");
return;
}

# route to PSTN dialed numbers starting with '+' or '00'
# (international format)
# - update the condition to match your dialing rules for PSTN routing
if(!($rU=~"^(\+|00)[1-9][0-9]{3,20}$"))
return;

# only local users allowed to call
if(from_uri!=myself) {
sl_send_reply("403", "Not Allowed");
exit;
}

if (strempty($sel(cfg_get.pstn.gw_port))) {
$ru = "sip:" + $rU + "@" + $sel(cfg_get.pstn.gw_ip);
} else {
$ru = "sip:" + $rU + "@" + $sel(cfg_get.pstn.gw_ip) + ":"
+ $sel(cfg_get.pstn.gw_port);
}

route(RELAY);
exit;
#!endif

return;
}

XMLRPC routing

#!ifdef WITH_XMLRPC
route[XMLRPC] {
# allow XMLRPC from localhost
if ((method=="POST" || method=="GET") && (src_ip==127.0.0.1)) {
# close connection only for xmlrpclib user agents
    if ($hdr(User-Agent) =~ "xmlrpclib")
        set_reply_close();
        set_reply_no_connect();
        dispatch_rpc();
    exit;
}
send_reply("403", "Forbidden");
exit;
}
#!endif

Routing to voicemail server

route[TOVOICEMAIL] {
#!ifdef WITH_VOICEMAIL
if(!is_method("INVITE|SUBSCRIBE"))
return;

# check if VoiceMail server IP is defined
if (strempty($sel(cfg_get.voicemail.srv_ip))) {
    xlog("SCRIPT: VoiceMail routing enabled but IP not defined\n");
    return;
}
if(is_method("INVITE")) {
    if($avp(oexten)==$null)
        return;
    $ru = "sip:" + $avp(oexten) + "@" + $sel(cfg_get.voicemail.srv_ip)+ ":" + $sel(cfg_get.voicemail.srv_port);
} else {
    if($rU==$null)
        return;
    $ru = "sip:" + $rU + "@" + $sel(cfg_get.voicemail.srv_ip)
+ ":" + $sel(cfg_get.voicemail.srv_port);
}
route(RELAY);
exit;
#!endif

return;
}

Manage outgoing branches

branch_route[MANAGE_BRANCH] {
    xdbg("new branch [$T_branch_idx] to $ru\n");
    route(NATMANAGE);
}

Manage incoming replies

onreply_route[MANAGE_REPLY] {
    xdbg("incoming reply\n");
    if(status=~"[12][0-9][0-9]")
        route(NATMANAGE);
}

Manage failure routing cases

failure_route[MANAGE_FAILURE] {
route(NATMANAGE);

if (t_is_canceled()) {
    exit;
}

#!ifdef WITH_BLOCK3XX
# block call redirect based on 3xx replies.
if (t_check_status("3[0-9][0-9]")) {
    t_reply("404","Not found");
    exit;
}
#!endif

#!ifdef WITH_VOICEMAIL
# serial forking
# - route to voicemail on busy or no answer (timeout)
if (t_check_status("486|408")) {
    $du = $null;
    route(TOVOICEMAIL);
    exit;
}
#!endif
}

Supports pseudo-variables to access and manage parts of the SIP messages and attributes specific to users and server.  Transformations to modify existing pseudo-variables, accessing only the wanted parts of the information. 

Already has over 1000 parameters, variables and functions exported to config file. Supports runtime update framework – to avoid restarting the SIP server when needing to change the config parameters

Tools

kamctl

Manage kamailio from command line, providing lots of operations, such as adding/removing/updating SIP users, controlling the ACL for users, managing the records for LCR or load balancing, viewing registered users and internal statistics, etc. When needed to interact with Kamailio, it does it via FIFO file created by mi_fifo module.

kamdbctl

Helps to configure and database needed by kamailio . First we need to select a database engine in the kamctlrc file by DBENGINE parameter .

Valid values are: MYSQL, PGSQL, ORACLE, DB_BERKELEY, DBTEXT.

The tool can be used to create and manage the database structure needed by Kamailio, therefore it should be immediately after Kamailio installation, in case you plan to run Kamailio with a database backend.

kamcmd

send RPC commands to Kamailio from command line , requires  ctl module

siremis

web management interface for Kamailio, written in PHP , AJAX , web 2.0 using MVC architecture

  • system and database administration tools for Kamailio SIP Server
  • subscriber, database aliases and speed dial management
  • location table view
  • dispatcher (load balancer), prefix-domain translation and least cost routing (lcr) management
  • access control lists (user groups) and permissions management
  • accounting records and missed calls vies
  • manage call data records (generated from acc records)
  • hash table, dial plan table and user preferences table management
  • offline message storage, presence service and sip trace views
  • communication with Kamailio SIP Server via XMLRPC ,  JSONRPC
  • communication with FreeSWITCH via event socket
  • create and display charts from statistic data stored by Kamailio
  • user location statistics charts
  • SIP traffic load charts
  • memory usage charts
  • accounting records charts and summary table
  • SQL-based CDR generation and rating billing engine

———————————–

Things covered in this article

  • Internal architecture
  • Configuration language
  • least cost routing
  • load balancing
  • traffic dispatching
  • DID routing
  • prefix based routing
  • SIP trunks and peering
  • traffic shaping
  • topology hiding
  • flood detection
  • scanning attacks prevention
  • anti-fraud policies

SQL and noSQL connectors

enum and DNS based routing

authentication and authorization

secure communication (TLS)

registration and location services

accounting and call data records

call control – redirect, forward, baring

redundancy and scalability

high availability and failover

websockets and webrtc

References :

Henning Westerholt – Kamailio project-1&1 Internet AG ( 2009 )

Proxying Media Streams via Kamailio’s RTP Proxy

Kamailio is a SIP server which does not play any role by itself in media transmission path. this behaviour leads to media packets having to attempt to stream peer to peer between caller and callee which in turn many a times causes them to get dropped in absence of NAT management

To ensure that media stream is proxied via an RTP proxy kamailio can use RTP proxy module combined with a RTP proxy.

This setup also provides other benefits such as controlling media media , security , Load balancing between many rtp proxies ,bridge signalling between multiple network interfaces etc.

RTP Proxy module

Used to proxy the media stream .

RTP proxies that can be used along with this module are:

RTP proxies can be used for bridging network interfaces , load distribution and balancing etc.It does not support transcoding.

Parameters :

rtpproxy_sock – binds a ip and port for rtp proxy

 modparam("rtpproxy", "rtpproxy_sock", "udp:localhost:12221")

rtpproxy_disable_tout – when rtp proxy is disabled then timeout till when it doesnt connect

rtpproxy_tout – timeout to wait for reply

rtpproxy_retr – num of retries after timeout

nortpproxy_str – sets the SDP attribute used by rtpproxy to mark the message’s SDP attachment with information that it have already been changed. Default value is

“a=nortpproxy:yes\r\n”

and others like

“a=sdpmangled:yes\r\n”

timeout_socket (string)

ice_candidate_priority_avp (string)

extra_id_pv (string)

db_url (string)

table_name (string)

rtp_inst_pvar (string)

Functions

set_rtp_proxy_set(setid) – Sets the Id of the rtpproxy set to be used for the next unforce_rtp_proxy(), rtpproxy_offer(), rtpproxy_answer() or rtpproxy_manage() command

rtpproxy_offer([flags [, ip_address]]) – to make the media pass through RTP the SDP is altered. Value of flag can be
1 – append first Via branch to Call-ID when sending command to rtpproxy.
2 – append second Via branch to Call-ID when sending command to rtpproxy. See flag ‘1’ for its meaning.
3 – behave like flag 1 is set for a request and like flag 2 is set for a reply
a – flags that UA from which message is received doesn’t support symmetric RTP. (automatically sets the ‘r’ flag)
b – append branch specific variable to Call-ID when sending command to rtpproxy
l – force “lookup”, that is, only rewrite SDP when corresponding session already exists in the RTP proxy
i, e – direction of the SIP message when rtpproxy is running in bridge mode. ‘i’ is internal network (LAN), ‘e’ is external network (WAN). Values ie , ei , ee and ii
x – shortcut for using the “ie” or “ei”-flags, to do automatic bridging between IPv4 on the “internal network” and IPv6 on the “external network”. Differentiated by IP type in the SDP, e.g. a IPv4 Address will always call “ie” to the RTPProxy (IPv4(i) to IPv6(e)) and an IPv6Address will always call “ei” to the RTPProxy (IPv6(e) to IPv4(i))
f – instructs rtpproxy to ignore marks inserted by another rtpproxy in transit to indicate that the session is already gone through another proxy. Allows creating a chain of proxies
r – IP address in SDP should be trusted. Without this flag, rtpproxy ignores address in the SDP and uses source address of the SIP message as media address which is passed to the RTP proxy
o – flags that IP from the origin description (o=) should be also changed.
c – flags to change the session-level SDP connection (c=) IP if media-description also includes connection information.
w – flags that for the UA from which message is received, support symmetric RTP must be forced.
zNN – perform re-packetization of RTP traffic coming from the UA which has sent the current message to increase or decrease payload size per each RTP packet forwarded if possible. The NN is the target payload size in ms, for the most codecs its value should be in 10ms increments, however for some codecs the increment could differ (e.g. 30ms for GSM or 20ms for G.723).
ip_address denotes the address of new SDP

such as : rtpproxy_offer(“FRWOC+PS”) is
rtpengine_offer(“force trust-address symmetric replace-origin replace-session-connection ICE=force RTP/SAVPF”);

route { 
... 
if (is_method("INVITE")) 
{ 
    if (has_body("application/sdp")) 
    { 
        if (rtpproxy_offer()) t_on_reply("1"); 
    } else { 
        t_on_reply("2"); 
    } 
} 

if (is_method("ACK") && has_body("application/sdp")) rtpproxy_answer(); 
... 
} 
onreply_route[1] { 
   if (has_body("application/sdp")) rtpproxy_answer(); 
} 
onreply_route[2] { 
   if (has_body("application/sdp")) rtpproxy_offer(); 
} 

rtpproxy_answer([flags [, ip_address]])- rewrite SDP to proxy media , it can be used from REQUEST_ROUTE, ONREPLY_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE.

rtpproxy_destroy([flags]) – tears down RTP proxy session for current call. Flags are ,
1 – append first Via branch to Call-ID
2 – append second Via branch to Call-ID
b – append branch specific variable to Call-ID
t – do not include To tag to “delete” command to rtpproxy thus causing full call to be deleted

unforce_rtp_proxy()

rtpproxy_manage([flags [, ip_address]]) – Functionality is to use predfined logic for handling requests
If INVITE with SDP, then do rtpproxy_offer()
If INVITE with SDP, when the tm module is loaded, mark transaction with internal flag FL_SDP_BODY to know that the 1xx and 2xx are for rtpproxy_answer()
If ACK with SDP, then do rtpproxy_answer()
If BYE or CANCEL, or called within a FAILURE_ROUTE[], then call unforce_rtpproxy().
If reply to INVITE with code >= 300 do unforce_rtpproxy()
If reply with SDP to INVITE having code 1xx and 2xx, then do rtpproxy_answer() if the request had SDP or tm is not loaded, otherwise do rtpproxy_offer()
This function can be used from ANY_ROUTE.

rtpproxy_stream2uac(prompt_name, count) – stream prompt/announcement pre-encoded with the makeann command. The uac/uas suffix selects who will hear the announcement relatively to the current transaction – UAC or UAS. Also used for music on hold (MOH).
Params : prompt_name – path name of the prompt to stream
count – number of times the prompt should be repeated. When count is -1, the streaming will be in loop indefinitely until the appropriate rtpproxy_stop_stream2xxx is issued.
Example rtpproxy_stream2xxx usage

if (is_method("INVITE")) { 
rtpproxy_offer();
if (is_audio_on_hold()) {
rtpproxy_stream2uas("/var/rtpproxy/prompts/music_on_hold", "-1");
} else {
rtpproxy_stop_stream2uas();
};
};

rtpproxy_stream2uas(prompt_name, count)

rtpproxy_stop_stream2uac()- Stop streaming of announcement/prompt/MOH

rtpproxy_stop_stream2uas()

start_recording()

Exported Pseudo Variables

$rtpstat

RPC Commands

rtpproxy.enable
rtpproxy.list

Ref : https://kamailio.org/docs/modules/5.3.x/modules/rtpproxy.html

Service Creation Environment (SCE ) for SIP Applications

I hoped of making a SIP application Development environment a year back and worked towards it earnestly . Sadly I wasn’t able to complete the job yet I have decided to share a few things about it here .

Aim :

Develop  a SCE ( Service Creation Environment ) to addresses all aspects of lifecycle of a Service, right from creation/development, orchestration, execution/delivery, Assurance and Migration/Upgrade of services.

Similar market products :

  • Open/cloud Rhino
  • Mobicents and Telestax

Limitations of open source/other market products:

  • Free versions of the Service Creation Environments do not offer High Availability.
  • High Cost of Deployment grade versions.

Solution Description

I propose a in-house Java based Service Creation Environment “SLC SCE”. The SLC SCE will enable creation of JAINSLEE based SIP  services. It can be used to develop and deploy carrier-grade applications that use SS7 and IMS based protocols such as INAP, CAP, Diameter and SIP as well as IT / Web protocols such as HTTP and XML.

Benefits:

  • Service Agility
  • Significantly Lower price points
  • Open Standards eliminate Legacy SCP Lock-in

Timeline

  • Java-based service creation environment (SCE) – 1.5 Months
  • Graphical User Interface (GUI) and schematic representations to help in the design, maintenance and support of applications – 1.5 months
  • SIP Resource Adapter – 1 month

Architecture

Service Creation Environment (SCE) for SIP Applications
Service Creation Environment (SCE) for SIP Applications

In essence it encompasses the idea of developing the following

  1. SIP stack
  2. Javascript API’s
  3. Java Libraries for calling SIP stack
  4. Eclipse plugin to work with the SIP application development process
  5. Visual Interface to view the logic of application and possible errors / flaws
  6. SDKs (  Service Development Kit) , which are development Environment themselves

Extra Effort required to put in to make the venture successful

  1. Demo applications for basic SIP logic like Call screening , call rerouting .
  2. tutorial to create , deploy and run application from scratch . Aimed at all sections ie web developer , telecom engineer , full stack developer etc .
  3. Some opensource implementation on public repositories like Github , Google code , SourceForge
  4. Perform active problem solving on Stackoverflow , CodeRanch , Google groups and  other forums .

—————————————————————

OfficeSIP

This post describes the installation , setup and configuration of Office SIP server to provide a registrar to our SIP based WebRTC application .

1. Get office SIP from this website

officesip0

2. Downloaded office sip executable on windows looks like this . double click on it to start installation .

officesip1

3.Installation screen appears as follows

officesip2

4. Terms and conditions

officesip3

5. Destination folder for installation

officesip4

6. Installing

officesip5

7. Validating install

officesip6

8. Installation completed

officesip7

9. Launch icon on dekstop

officesip8

10 . Office SIP web login screen

officesip9

11. create account ( also known as realm or domain ) for users to register in their SIP and webrtc sip agents

officesip10

12. Fill in account details for every account added to officeSIP

officesip11

13. add users that will be registering to officeSIP server

officesip13

14.Office SIP settings file can be modified for changing server parameters like ip and port

officesip14_001

15 . Office SIP can now be used by sip agents like softphones , webRTC pages , etc to register with OfficeSIP server


BEA Weblogic SIP server

Bea server is a old SIP servlet container ie application server which is used to embed control logic in a program . It is supported on jdk1.5 hence the system’s environment variables must match . Otherwise in later stages deploying applications throw class version error .

1. Install Bea Weblogic

2. Follow the Installation steps

Make domain

3. Goto the installation directory . Usually C:/bea/user_projects/mydomain/ .

click on startweblogic.cmd in windows. In case the system is linux run startweblogic.sh script

4. Open Web console on url : http://127.0.0.1:7001/console. Enter username password

default username password weblogic , weblogic .

It can also be customized for example my username and password are altanai , tcs@1234

5.  Make Converged SIP Servlet Application in any editor such as notepad , edit+ etc .

The project structure looks like

Call screening
src
build
src
web
build.xml

The SIP servlet are put side directory structure of src

For example : sample application for Call screening

package com.altanai.voice;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.sip.*;
import javax.servlet.sip.Proxy;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.util.*;
public class CallScreening extends SipServlet
{
private static SipFactory factory;
private static SipApplicationSession sas;
private static Proxy proxy;
public void init(ServletConfig config) throws ServletException
{
System.out.println(“Call screening SIP servlet initiated”);
super.init(config);
}
protected void doInvite(SipServletRequest req) throws java.lang.IllegalArgumentException,java.lang.IllegalStateException,javax.servlet.ServletException,java.io.IOException
{
System.out.println(“Received an Invite Request”);
if(req.getFrom().toString().indexOf(“alice”)!=-1)
{
req.createResponse(406).send();
System.out.println(“User is blocked”);
}
else
{
req.createResponse(200).send();
System.out.println(“User is not blocked”);
}
}
}

6. Build it with ant . For this go inside the application folder and run ant. Output will either be “failed to build “ or “build successfully” .

The ant  command generates the war file from SIP servlet Web application .

7. Incase of successful build . Add the application to Weblogic web console install section and activate it .

I will demonstrate this process in step by step manner . First  click on “ Lock and Edit “ Button on the left panel . Then goto Install button in the centre area and browser to the location of application war or sar we have build through ant ,

8. We can delete an application in exactly the same way . click on “ Lock and Edit “ Button on the left panel . Then goto the delete button after selecting the radio button alongside the application we want to delete.

8. For enhanced application building we can also refer to sample provided along with bea weblogic . file:///C:/bea/sipserver30/samples/sipserver/examples/src/index.html

SIP Presence

We have already learned about Sip user agent and sip network server. SIP clients initiates a call and SIP server routes the call . Registrar is responsible for name resolution and user location. Sip proxy receives calls and send it to its destination or next hop.

Presence is user’s reachability and willingness to communicate its current status information . User subscribe to an event and receive notification . The components in presence are :

Presence user agentpresence components
Presence agent
Presence server
Watcher

Image source  : http://msdn.microsoft.com/en-us/library/bb896003.aspx

Sip was initially introduced as a signaling protocol but there were Lack of method to emulate constant communication and update status between entity
Three more method was introduced namely – Publish , Subscribe and Notify

Subscribe request should be send by watchers to presence server
Presence agent should authenticate and send acknowledgement
State changes should be notified to subscriber
Agents should be able to allow or terminate subscription

presence flow

Image source http://download.oracle.com/docs/cd/B32110_01/ocms.1013/b31497/about_sdp.htm#BABDHHCJ

Traces of various SIP requetss and response in presence are are follows :

subscribe request

SUBSCRIBE sip:presentity@example.com SIP/2.0
      Via: SIP/2.0/UDP host.example.com;branch=z9hG4bKnashds7
      To: <sip:presentity@example.com>
      From: <sip:watcher@example.com>;tag=12341234
      Call-ID: 12345678@host.example.com
      CSeq: 1 SUBSCRIBE
      Max-Forwards: 70
      Expires: 3600
      Event: presence
      Contact: sip:user@host.example.com
      Content-Length: 0
 

200 OK to subscribe request

SIP/2.0 200 OK
      Via: SIP/2.0/UDP host.example.com;branch=z9hG4bKnashds7
       ;received=192.0.2.1
      To: <sip:presentity@example.com>;tag=abcd1234
      From: <sip:watcher@example.com>;tag=12341234
      Call-ID: 12345678@host.example.com
      CSeq: 1 SUBSCRIBE
      Contact: sip:pa.example.com
      Expires: 3600
      Content-Length: 0
 

Notify Request

NOTIFY sip:user@host.example.com SIP/2.0
      Via: SIP/2.0/UDP pa.example.com;branch=z9hG4bK8sdf2
      To: <sip:watcher@example.com>;tag=12341234
      From: <sip:presentity@example.com>;tag=abcd1234
      Call-ID: 12345678@host.example.com
      CSeq: 1 NOTIFY
      Max-Forwards: 70
      Event: presence
      Subscription-State: active; expires=3599
      Contact: sip:pa.example.com
      Content-Type: application/pidf+xml
      Content-Length: …
 

200 OK success response to notify

SIP/2.0 200 OK
      Via: SIP/2.0/UDP pa.example.com;branch=z9hG4bK8sdf2
       ;received=192.0.2.2
      To: <sip:watcher@example.com>;tag=12341234
      From: <sip:presentity@example.com>;tag=abcd1234
      Call-ID: 12345678@host.example.com
      CSeq: 1 NOTIFY
 

PUBLISH Request

PUBLISH sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK652hsge
To: <sip:presentity@example.com>
From: <sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
Max-Forwards: 70
Expires: 3600
Event: presence
Content-Type: application/pidf+xml
Content-Length: …

200 OK success response to PUBLISH

SIP/2.0 200 OK
Via: SIP/2.0/UDP pua.example.com;branch=z9hG4bK652hsge
;received=192.0.2.3
To: <sip:presentity@example.com>;tag=1a2b3c4d
From: <sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
SIP-ETag: dx200xyz
Expires: 1800

A call flow depicting presence in action is as given below :

presence subscribe notify

Image source http://www.cisco.com/en/US/i/100001-200000/190001-200000/190001-191000/190463.jpg

security considerations for Presence service include:

  • Access control.
  • Notifier privacy mechanism.
  • Denial of service attacks.
  • Replay Attacks.
  • Man-in-the-middle attacks.
  • Confidentiality.

some solutions for security implementation are

  • Sip registration
    TLS
    Digest Authentication
    S/MIME

References :

Rfc 3856 http://www.ietf.org/rfc/rfc3856.txt
Rfc 3265 http://www.ietf.org/rfc/rfc3265.txt
Rfc 2778 http://www.ietf.org/rfc/rfc2778.txt
Rfc 3261 http://www.ietf.org/rfc/rfc3261.txt
Rfc 3903 http://www.ietf.org/rfc/rfc3903.txt
http://en.wikipedia.org/wiki/Session_Initiation_Protocol

Summary :

Presence is a way to have sustained stateful communication. The SIP User agents can use presence service to know about others user’s online status . Presnece deployment must confirm to security standards .

Interoperability between WebRTC , SIP phones and others

WebRTC SIP clients

What is the role of SIP server ?

SIP Server convert the SIP transport from WebSocket protocol to UDP, TCP or TLS which are supported by all legacy networks. It also facilitates the use of rich serves such as phonebook synchronisation , file sharing , oauth in client .

How does WebRTC Solution traverse through FireWalls ?

NAT traversal across Firewalls is achieved via TURN/STUN through ICE candidates gathering .Current ice_servers are : stun:stun.l.google.com:19302 and  turn:user@numb.viagenie.ca

What audio and video codecs are supported by WebRTC client side alone ?

Without the role of Media Server WebRTC solution supports Opus , PCMA , PCMU for audio and VP8 for video call.

RTCBreaker if enabled provides a third party B2BUA agent that performs certain level of codec conversion to H.264, H.263, Theora or MP4V-ES for non WebRTC supported agents.

What video resolution is supported by WebRTC solution ?

The browser will try to find the best video size between max and min based on the camera capabilities.

Options are : sqcif | qcif | qvga | cif | hvga | vga | 4cif | svga | 480p | 720p | 16cif | 1080p

We can also predefine the video size such as minWidth, minHeight, maxWidth, maxHeight.

What bandwidth is required to run WebRTC solution ?

We can set maximum audio and video bandwidth to use or use the browser’s ability to set it hy default at runtime . This will change the outgoing SDP to include a “b:AS=” attribute. Browser negotiates the right value using RTCP-REMB and congestion control.

SIPML5 client by dubango

calltakenoffhold

Telestax WebRTC client

2014-06-11_2215

SIPJS with flash network support

windows_IE_1

JSSIP – MIT license 2014-02-09_1444

SIP phones in Ubuntu ( Linux system)

SFL phone

linux sfl 2 linux sfl 1

Yate SIP phone

linux yate 2 linux yate 1

Linphone

ubuntulinphon4 linuxlinphone2

Windows Operating system SIP software

Xlite is well known SIP softphone for windows dessktop

xlite 1

Xlite new version

windows_xlite_7 windows_xlite_6_001 windows_xlite_6 windows_xlite_3

Kapanga SIP softphone . It is also runnable on Linux desktop through windows compatibility softwares like wine

windows_kapanga_3 windows_kapanga_2

FreeSwitch Communicator , comes along with the Freeswitch Media Server .

windows_freeswitchcomm__2 windows_freeswitch_comm_3

Boghe SIP RCS client

windows_boghe_5 windows_boghe_4 windows_boghe_2 windows_boghe_1

Jitsi SIP phone

jitsi 2 jitsi 1

MAC SIP software

idoubs desktop SIP RCS client for Mac

Screen shot 2014-06-13 at 4.03.27 PM

iOS SIP phone applications

Linphone

IMG-20140703-WA0003  IMG-20140703-WA0006 IMG-20140703-WA0007  IMG-20140710-WA0001 IMG-20140710-WA0002

Android SIP applications

Sipdroid , opensource

Screenshot_2014-07-01-19-36-47 Screenshot_2014-07-01-19-37-00 Screenshot_2014-07-01-19-37-44 Screenshot_2014-07-01-19-37-54 Screenshot_2014-07-01-19-38-46


Kamailio Call routing and Control

Kamailio SIP server evolved from SER and OpenSER. Written in ANSI C , primarily it is an open source proxy SIP server. RFC 3261 compliant and has support for various Operating system to install and run on as alpine , centos , deb , fedora , freebsd , netbsd , obs , openbsd , opensuse , oracle , rhel , solaris ,

With modular design it already has 150 + modules and can have third part addons like Databases , RTP engines etc. Anyone can contribute to extensions and modules , read here .

It also posses cmd line tool kamcmd , kamcli as well as Web management interface SIREMIS .

It has provisions for complex routing logic development through scripts and programming languages interpreter support.

Over the years kamailio as proven a key component of a “carrier-grade” SIP service delivery platform. Either as SBC interfacing internal softswitch with public internet and handling complex operation as NAT, auth , flood control, topology hiding etc or even as the core SIP Server handling RTP relay as well.

Kamailio’s call routing log can be divided into:

  • Core functions
  • Core modules needed for almost any useful configuration like transaction module , Record route module etc ( read more https://telecom.altanai.com/2014/11/18/kamailio-modules/)
  • Ancillary modules to provide specific functionality (e.g. JANSSON , PIKE)
  • Pseudo-variables , which hold read/writeable attributes and
  • Transformations and custom logic definition.

Kamailio config

kamailio confguration file should be composed of
Core configuration directives as

!ifdef WITH_MULTIDOMAIN
!define MULTIDOMAIN 1
!else
!define MULTIDOMAIN 0
!endif

Global Parameters like

memdbg=5
memlog=5
log_facility=LOG_LOCAL0
fork=yes
children=4

Loading Modules

loadmodule "corex.so"
loadmodule "tm.so"
loadmodule "tmx.so"
loadmodule "sl.so"
loadmodule "rr.so"

Module parameters
For example considering for tm auto-discard branches from previous serial forking leg as failure_reply_mode ,30 sec as default retransmission timeout with 120 sec as invite retransmission timeout after 1xx

modparam("tm", "failure_reply_mode", 3)
modparam("tm", "fr_timer", 30000)
modparam("tm", "fr_inv_timer", 120000)

Subroutines (in essence, SIP event callbacks):
Request routes (request_route)
Reply routes (onreply_route)
Failure routes (failure_route)
Branch routes

For example consider main sip routing block

request_route {
    route(REQINIT);
    route(NATDETECT);
    if (is_method("CANCEL"))
    {
        if (t_check_trans()) {
            route(RELAY);
        }
        exit;
    }
    route(WITHINDLG);
    t_check_trans();
    route(AUTH);
    if (is_method("INVITE|SUBSCRIBE"))
        record_route();
    route(SIPOUT);
    route(PRESENCE);
    route(REGISTRAR);
    ...
}

Custom event routes (callbacks/event handlers exposed by modules).
Code for programming languages and runtimes:
String transformations
Variables
Ephemeral/scratch-pad variables ($var(…))
Transaction-persistent variables ($avp(…)/$xavp(…)) , extended AVP like AVP ar attached to transactions and not messages .
Dialog-persistent variables ($dlg_var(…))

$var(rc) = $rc;
route(TOVOICEMAIL);
t_newtran();
switch ($var(rc)) {
    case -1:
    case -3:
        send_reply("404", "Not Found");
        exit;
    case -2:
        send_reply("405", "Method Not Allowed");
        exit;
}

This article describes call routing config for Kamailio under following roles

  • SIP Proxy
  • Registrar
  • Accountant
  • Session border Controller

Kamailio as Proxy Server

Simple Kamailio configuration with basic features like alias , accounting , record routing , handling SIP requests like INVITE and its replies . Also failure and NAT handling . More samples of Kamailio config and call routing are at https://github.com/altanai/kamailioexamples

!KAMAILIO

 # Defined Values
 !substdef "!MY_IP_ADDR!!g"
 !substdef "!MY_EXTERNAL_IP!!g"
 !substdef "!MY_UDP_PORT!!g"
 !substdef "!MY_TCP_PORT!!g"
 !substdef "!MY_UDP_ADDR!udp:MY_IP_ADDR:MY_UDP_PORT!g"
 !substdef "!MY_TCP_ADDR!tcp:MY_IP_ADDR:MY_TCP_PORT!g"
 !define MULTIDOMAIN 0
 - flags
 FLT_ - per transaction (message) flags
 FLB_ - per branch flags
 !define FLT_ACC 1
 !define FLT_ACCMISSED 2
 !define FLT_ACCFAILED 3
 !define FLT_NATS 5
 !define FLB_NATB 6
 !define FLB_NATSIPPING 7

 # Global Parameters
 LOG Levels: 3=DBG, 2=INFO, 1=NOTICE, 0=WARN, -1=ERR
 debug=2
 log_stderror=no
 memdbg=5
 memlog=5
 log_facility=LOG_LOCAL0
 log_prefix="{$mt $hdr(CSeq) $ci} "

 /* number of SIP routing processes */
 children=2
 /* uncomment the next line to disable TCP (default on) */
 disable_tcp=yes
 /* uncomment the next line to disable the auto discovery of local aliases based on reverse DNS on IPs (default on) */ 
 auto_aliases=no

 /* add local domain aliases */
 alias="sip.mydomain.com"

 /* listen addresses */
 listen=udp:127.0.0.1:5060
 listen = MY_UDP_ADDR advertise MY_EXTERNAL_IP:MY_UDP_PORT
 listen = MY_TCP_ADDR advertise MY_EXTERNAL_IP:MY_TCP_PORT

 # Modules Section
 loadmodule "jsonrpcs.so"
 loadmodule "kex.so"
 loadmodule "corex.so"
 loadmodule "tm.so"
 loadmodule "tmx.so"
 loadmodule "sl.so"
 loadmodule "rr.so"
 loadmodule "pv.so"
 loadmodule "maxfwd.so"
 loadmodule "textops.so"
 loadmodule "siputils.so"
 loadmodule "xlog.so"
 loadmodule "sanity.so"
 loadmodule "ctl.so"
 loadmodule "cfg_rpc.so"
 loadmodule "acc.so"
 loadmodule "counters.so"

 ----------------- setting module-specific parameters --------------

 ----- jsonrpcs params -----
 modparam("jsonrpcs", "pretty_format", 1)
 /* set the path to RPC fifo control file */
 modparam("jsonrpcs", "fifo_name", "/var/run/kamailio/kamailio_rpc.fifo")
 /* set the path to RPC unix socket control file */
 modparam("jsonrpcs", "dgram_socket", "/var/run/kamailio/kamailio_rpc.sock")

 ----- ctl params -----
 /* set the path to RPC unix socket control file */
 modparam("ctl", "binrpc", "unix:/var/run/kamailio/kamailio_ctl")

 ----- tm params -----
 auto-discard branches from previous serial forking leg
 modparam("tm", "failure_reply_mode", 3)
 default retransmission timeout: 30sec
 modparam("tm", "fr_timer", 30000)
 default invite retransmission timeout after 1xx: 120sec
 modparam("tm", "fr_inv_timer", 120000)
 
----- rr params -----
 set next param to 1 to add value to ;lr param (helps with some UAs)
 modparam("rr", "enable_full_lr", 0)
 do not append from tag to the RR (no need for this script)
 modparam("rr", "append_fromtag", 0)

 ----- acc params -----
 /* what special events should be accounted ? / modparam("acc", "early_media", 0) modparam("acc", "report_ack", 0) modparam("acc", "report_cancels", 0) / by default ww do not adjust the direct of the sequential requests.
 if you enable this parameter, be sure the enable "append_fromtag"
 in "rr" module / modparam("acc", "detect_direction", 0) / account triggers (flags) */
 modparam("acc", "log_flag", FLT_ACC)
 modparam("acc", "log_missed_flag", FLT_ACCMISSED)
 modparam("acc", "log_extra",
 "src_user=$fU;src_domain=$fd;src_ip=$si;"
 "dst_ouser=$tU;dst_user=$rU;dst_domain=$rd")
 modparam("acc", "failed_transaction_flag", FLT_ACCFAILED) 

 # Routing Logic

 /* Main SIP request routing logic*/
 request_route {
 per request initial checks
 route(REQINIT);
 CANCEL processing
 if (is_method("CANCEL")) {
     if (t_check_trans()) {
         route(RELAY);
     }
     exit;
 }
 handle retransmissions
 if (!is_method("ACK")) {
     if(t_precheck_trans()) {
         t_check_trans();
         exit;
     }
     t_check_trans();
 }
 handle requests within SIP dialogs
 route(WITHINDLG);
 only initial requests (no To tag)
 record routing for dialog forming requests (in case they are routed)
 - remove preloaded route headers
 remove_hf("Route");
 if (is_method("INVITE|SUBSCRIBE")) {
     record_route();
 }
 account only INVITEs
 if (is_method("INVITE")) {
     setflag(FLT_ACC); # do accounting
 }
 if ($rU==$null) {
     # request with no Username in RURI
     sl_send_reply("484","Address Incomplete");
     exit;
 }
 update $du to set the destination address for proxying
 $du = "sip:" + $rd + ":9";
 route(RELAY);
 exit;
 } 
 
#Wrapper for relaying requests
 route[RELAY] {
if (is_method("INVITE|BYE|SUBSCRIBE|UPDATE")) {     if(!t_is_set("branch_route")) t_on_branch("MANAGE_BRANCH"); 
} 

if (is_method("INVITE|SUBSCRIBE|UPDATE")) {     if(!t_is_set("onreply_route")) t_on_reply("MANAGE_REPLY"); 
} 

if (is_method("INVITE")) {     
if(!t_is_set("failure_route")) t_on_failure("MANAGE_FAILURE"); 
} 

if (!t_relay()) {     sl_reply_error(); } exit;
 }
 
#Per SIP request initial checks
 route[REQINIT] {
     if($ua =~ "friendly-scanner|sipcli|VaxSIPUserAgent") {
         # sl_send_reply("200", "OK");
         exit;
     }
 if (!mf_process_maxfwd_header("10")) {     
sl_send_reply("483","Too Many Hops");     
exit; 
}

if(is_method("OPTIONS") && uri==myself && $rU==$null) {     sl_send_reply("200","Keepalive");     
exit; 
} 

if(!sanity_check("1511", "7")) {     
xlog("Malformed SIP message from $si:$sp\n");     
exit; 
}
}

# Handle requests within SIP dialogs
 route[WITHINDLG] {
     if (!has_totag()) return;
if (loose_route()) {     
if (is_method("BYE")) {         
setflag(FLT_ACC); # do accounting ...         setflag(FLT_ACCFAILED); # ... even if the transaction fails     
} else if ( is_method("NOTIFY") ) {
         # Add Record-Route for in-dialog NOTIFY as per RFC 6665.         record_route();     
}     
route(RELAY);     
exit; 
} 

if ( is_method("ACK") ) {     
if ( t_check_trans() ) {         # no loose-route, but stateful ACK;         must be an ACK after a 487 or e.g. 404 from upstream server         route(RELAY);        
 exit;     
} else {
         # ACK without matching transaction , ignore and discard         exit;     
} 
} sl_send_reply("404","Not here"); exit;
}

#Manage outgoing branches
 branch_route[MANAGE_BRANCH] {
     xdbg("new branch [$T_branch_idx] to $ru\n");
 }

#Manage incoming replies
 onreply_route[MANAGE_REPLY] {
     xdbg("incoming reply\n");
 }

#Manage failure routing cases
 failure_route[MANAGE_FAILURE] {
     if (t_is_canceled()) exit;
 }




Controlling Call Routing from command Line

To find the loaded flags while starting kamailio

kamailio -v
version: kamailio 5.1.8 (x86_64/linux) d8e930
flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES
ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144 MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB
poll method support: poll, epoll_lt, epoll_et, sigio_rt, select.
id: d8e930 
compiled on 09:47:09 May  3 2019 with gcc 4.8.4

kamdbctl

creates the database support for many kamailio modules such as auth , location , dispatcher , permission etc

make sure you load a DB engine , during kamailio installation and configuration . It can be either done though make command or though modules.lst file

 make include_modules="db_mysql" cfg
 make all
 make install

since json replaced all fifo command, ensure you do not get "json.h: No such file or directory” in server by install json either via libjson-c-dev or libjson-cpp-dev

apt-get install libjson-c-dev 

For uuid/uuid.h: No such file or directory install

apt-get install uuid-dev

For libpq-fe.h: No such file or directory install

apt-get install libpq-dev

kamdbctl command list

kamdbctl create <db name or db_path, optional> ...(creates a new database)
kamdbctl drop <db name or db_path, optional> .....(!entirely deletes tables!)
kamdbctl reinit <db name or db_path, optional> ...(!entirely deletes and than re-creates tables!)
kamdbctl backup <file> ...........................(dumps current database to file)
kamdbctl restore <file> ..........................(restores tables from a file)
kamdbctl copy <new_db> ...........................(creates a new db from an existing one)
kamdbctl presence ................................(adds the presence related tables)
kamdbctl extra ...................................(adds the extra tables)
kamdbctl dbuid ...................................(adds the uid tables)
kamdbctl dbonly ..................................(creates empty database)
kamdbctl grant ...................................(grant privileges to database)
kamdbctl revoke ..................................(revoke privileges to database)
kamdbctl add-tables <gid> ........................(creates only tables groupped in gid)

if you want to manipulate database as other database user than
root, want to change database name from default value "kamailio",
or want to use other values for users and password, edit the
"config vars" section of the command kamdbctl.

kamdbctl pframework create .......................(creates a sample provisioning framework file)

For psql: received invalid response to SSL negotiation: [
ERROR: Creating database failed!
errors . Remember for mysql the defaul port is 3306, but for psql it is 5432 . Hence make the change in /etc/kamailio/kamctlrc

database port
DBPORT=3306
DBPORT=5432  

Kamctl

If kamctl isnt accessible from the machine installed with kamailio , just goto kamctl folder and compile it yourself . For example for me , I took the git pull of kamailio source code v 5.1.0 and went to util folder

cd  /kamailio_source_code/utils/kamctl 
make && make install 

some commands

‘start|stop|restart|trap’
‘acl’ – manage access control lists (acl)
‘lcr’ – manage least cost routes (lcr)
‘cr’ – manage carrierroute tables show|reload|dump
‘rpid’ – manage Remote-Party-ID (RPID)
‘add|passwd|rm’ – manage subscribers
‘add|dump|reload|rm|show’ – manage trusted
‘add|dump|reload|rm|show’ – manage address
‘add|dump|reload|rm|show’ – manage address
‘dispatcher’ – manage dispatcher

dispatcher add 1 sip:1.2.3.1:5050 1 5 'prefix=proxycall' 'gatewaye33'

‘dialog’ – manage dialog records
‘srv’ – server management commands
‘cisco_restart’ – restart CISCO phone (NOTIFY)
‘online’ – dump online users from memory
‘monitor’ – show internal status

[cycle #: 3; if constant make sure server lives]
Kamailio Runtime Details: 
kamailio 5.1.8 (x86_64/linux) d8e930
    now:  Fri May 24 13:39:19 2019
    up_since: Fri May 24 13:31:37 2019
    uptime: 462

Transaction Statistics: 
    tmx:UAS_transactions = 0        tmx:UAC_transactions = 0        tmx:active_transactions = 0     tmx:inuse_transactions = 0

Stateless Server Statistics: 
    sl:sent_replies = 0            sl:sent_err_replies = 0

UsrLoc Statistics: 
    usrloc:location-contacts = 0        usrloc:location-expires = 0         usrloc:location-users = 0           usrloc:registered_users = 0

Core Statistics: 
    core:rcv_requests = 0        core:fwd_requests = 0       core:rcv_replies = 0        core:fwd_replies = 0

Shared Memory Statistics: 
    shmem:fragments = 1                shmem:max_used_size = 2807640       shmem:total_size = 67108864
    shmem:free_size = 64301224            shmem:real_used_size = 2807640      shmem:used_size = 2566040

‘ping’ – ping a SIP URI (OPTIONS)
‘ul|alias’ – manage user location or aliases
‘ps’ – print details about running processes
‘ps’ – print details about running processes
‘stats’ – print internal statistics

{
  "jsonrpc":  "2.0",
  "result": [
    "core:bad_URIs_rcvd = 0",
    "core:bad_msg_hdr = 0",
    "core:drop_replies = 0",
    "core:drop_requests = 0",
    "core:err_replies = 0",
    "core:err_requests = 0",
    "core:fwd_replies = 0",
    "core:fwd_requests = 0",
    "core:rcv_replies = 0",
    "core:rcv_replies_18x = 0",
    "core:rcv_replies_1xx = 0",
    "core:rcv_replies_2xx = 0",
    "core:rcv_replies_3xx = 0",
    "core:rcv_replies_401 = 0",
    "core:rcv_replies_404 = 0",
    "core:rcv_replies_407 = 0",
    "core:rcv_replies_480 = 0",
    "core:rcv_replies_486 = 0",
    "core:rcv_replies_4xx = 0",
    "core:rcv_replies_5xx = 0",
    "core:rcv_replies_6xx = 0",
    "core:rcv_requests = 0",
    "core:rcv_requests_ack = 0",
    ...
}

‘rpc’ – send raw RPC commands

Kamcmd

unix tool for interfacing with Kamailio using exported RPCs. It uses binrpc (a proprietary protocol, designed for minimal packet size and fast parsing) over a variety of transports (unix stream sockets, unix datagram sockets, udp or tcp).

 cfg.add_group_inst
 cfg.commit
 cfg.del
 cfg.del_delayed
 cfg.del_group_inst
 cfg.diff
 cfg.get
 cfg.help
 cfg.list
 cfg.reset
 cfg.rollback
 cfg.set
 cfg.set_delayed
 cfg.set_delayed_int
 cfg.set_delayed_string
 cfg.set_now_int
 cfg.set_now_string
 cfg.seti
 cfg.sets
 cnt.get
 cnt.get_raw
 cnt.get_vars
 cnt.grp_get_all
 cnt.grps_list
 cnt.help
 cnt.list_groups
 cnt.list_vars
 cnt.reset
 cnt.var_list
 core.aliases_list
 core.arg
 core.echo
 core.flags
 core.info
 core.kill
 core.modules
 core.ppdefines
 core.printi
 core.prints
 core.ps
 core.psx
 core.pwd
 core.shmmem
 core.sockets_list
 core.tcp_info
 core.tcp_list
 core.tcp_options
 core.udp4_raw_info
 core.uptime
 core.version
 corex.debug
 corex.list_aliases
 corex.list_sockets
 corex.pkg_summary
 corex.shm_status
 corex.shm_summary
 ctl.connections
 ctl.listen
 ctl.who
 dns.add_a
 dns.add_aaaa
 dns.add_srv
 dns.debug
 dns.debug_all
 dns.delete_a
 dns.delete_aaaa
 dns.delete_all
 dns.delete_all_force
 dns.delete_cname
 dns.delete_ebl
 dns.delete_naptr
 dns.delete_ptr
 dns.delete_srv
 dns.delete_txt
 dns.lookup
 dns.mem_info
 dns.view
 dst_blacklist.add
 dst_blacklist.debug
 dst_blacklist.delete_all
 dst_blacklist.mem_info
 dst_blacklist.view
 jsonrpc.echo
 mod.stats
 pkg.stats
 pv.shvGet
 pv.shvSet
 sl.stats
 stats.clear_statistics
 stats.fetch
 stats.get_statistics
 stats.reset_statistics
 system.listMethods
 system.methodHelp
 system.methodSignature
 tm.cancel
 tm.clean
 tm.hash_stats
 tm.list
 tm.reply
 tm.reply_callid
 tm.stats
 tm.t_uac_start
 tm.t_uac_wait
 ul.add
 ul.db_contacts
 ul.db_expired_contacts
 ul.db_users
 ul.dump
 ul.flush
 ul.lookup
 ul.rm
 ul.rm_contact
 alias: ps
 alias: psx
 alias: list
 alias: ls
 alias: ver
 alias: version
 alias: who
 alias: listen
 alias: dns_mem_info
 alias: dns_debug
 alias: dns_debug_all
 alias: dst_blacklist_mem_info
 alias: dst_blacklist_debug
 builtin: ?
 builtin: help
 builtin: version
 builtin: quit
 builtin: exit
 builtin: warranty
 builtin: license

some examples of the kamcmd commands

stats

kamctl kamcmd 
tm.stats 
{     
current: 0     
waiting: 0     
total: 0     
total_local: 0     
rpl_received: 0     
rpl_generated: 0     
rpl_sent: 0     
6xx: 0     
5xx: 0     
4xx: 0     
3xx: 0     
2xx: 0     
created: 0     
freed: 0     
delayed_free: 0 
}

Get info about TLS

kamcmd> tls.info
{
    max_connections: 2048
    opened_connections: 1
    clear_text_write_queued_bytes: 0
}

Get ifno about open sockets

kamcmd> core.sockets_list
{
    socket: {
        proto: udp
        address: 1.2.3.4
        port: 5060
        mcast: no
        mhomed: no
    }
    socket: {
        proto: tcp
        address:  1.2.3.4
        port: 5060
        mcast: no
        mhomed: no
    }
    socket: {
        proto: tcp
        address:  1.2.3.4
        port: 80
        mcast: no
        mhomed: no
    }
    socket: {
        proto: tls
        address:  1.2.3.4
        port: 5061
        mcast: no
        mhomed: no
    }
    socket: {
        proto: tls
        address:  1.2.3.4
        port: 443
        mcast: no
        mhomed: no
    }
}

get core info

kamcmd> core.info
{
    version: kamailio 5.2.3
    id: 4a4588 
    compiler: gcc 5.4.0
    compiled: 15:54:50 Jun 27 2019
    flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES
}

SIP and SDP Messages Explained

Traditional SIP headers for Call setup are INVITE, ACK and teardown are CANCEL or BYE
However with more adoption newer methods specific to services were added such as
MESSAGE Methods for Instant Message based services
SUBSCRIBE, NOTIFY standardised by Event notification extension RFC 3856
PUBLISH to push presence information to the network

Outlining the SIP Requests and Responses in tables below,

1. Request Message

Request Message

Description

REGISTERA Client use this message to register an address with a SIP server
INVITEA User or Service use this message to let another user/service participate in a session. The body of this message would include a description of the session to which the callee is being invited.
ACKThis is used only for INVITE indicating that the client has received a final response to an INVITE request
CANCELThis is used to cancel a pending request
BYEA User Agent Client use this message to terminate the call
OPTIONSThis is used to query a server about its capabilities

2. Response Message

Code

Category

Description

1xxProvisionalThe request has been received and processing is continuing
2xxSuccessAn ACK, to indicate that the action was successfully received, understood, and accepted.
3xxRedirectionFurther action is required to process this request
4xxClient ErrorThe request contains bad syntax and cannot be fulfilled at this server
5xxServer ErrorThe server failed to fulfill an apparently valid request
6xxGlobal FailureThe request cannot be fulfilled at any server

, based on RFC 3261

SIP headers :

Display names

From originators sipuri

CSeq or Command Sequence contains an integer and a method name. The CSeq number is incremented for each new request within a dialog and is a traditional sequence number.

Contact – SIP URI that represents a direct route to the originator usually composed of a username at a fully qualified domain name (FQDN). While an FQDN is preferred, many end systems do not have registered domain names, so IP addresses are permitted. The Contact header field tells other elements where to send future requests.

Max-Forwards -to limit the number of hops a request can make on the way to its destination. It consists of an integer that is decremented by one at each hop.

Content-Type – description of the message body. ex : application/h.323

Content-Length – an octet (byte) count of the message body.

Accept – acceptable formats like application/sdp or currency/dollars

Authorization – encryption info

Call-Id uniquely identify a session

contact – sip url alternative for direct routing

Encryption

Expires – when msg content is no longer valid

Mandatory SIP headers

  • INVITE sip:altanai@domain.comSIP/2.0
  • Via: SIP/2.0/UDP host.domain.com:5060
  • From: Bob <sip:bob@domain.com>
  • To: Altanai <sip:domain@wcom.com>
  • Call-ID: 163784@host.domain.com
  • CSeq: 1 INVITE

session description in SDP

sdp

SDP /Session Description Protocol

standard for protocol definition for exchange of media ( RFC 4566)

SDP is encapsulated inside of SIP packet

TYPICAL SIP INVITE :

INVITEnbspsip:01150259917040@x.x.x.x SIP/2.0
 Via: SIP/2.0/UDP x.x.x.x:5060branch=z9hG4bK400fc6e6
 From: "123456789" ltsip:123456789@x.x.x.xgttag=as42e2ecf6
 To: ltsip:01150259917040@x.x.x.x.4gt
 Contact: ltsip:123456789@x.x.x.x4gt
 Call-ID: 2485823e63b290b47c042f20764d990a@x.x.x.x.x
 CSeq: 102 INVITE
 User-Agent:nbspMatrixSwitch
 Date: Thu, 22 Dec 2005 18:38:28 GMT
 Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER
 Content-Type: application/sdp
 Content-Length: 268
 v=0
 o=root 14040 14040 IN IP4 x.x.x.x
 s=session
 c=IN IP4 x.x.x.x
 t=0 0
 m=audio 26784 RTP/AVP 0 8 18 101
 a=rtpmap:0 PCMU/8000
 a=rtpmap:8 PCMA/8000
 a=rtpmap:18 G729/8000
 a=rtpmap:101 telephone-event/8000
 a=fmtp:101 0-16
 a=fmtp:18nbspannexb=no - - - -
 c=* (connection information - optional if included at session-level)
 b=* (bandwidth information)
 a=* (zero or more media attribute lines)

SIP Responses

1xx—Provisional Responses

response that tells to its recipient that the associated request was received but result of the processing is not known yet which could be if the processing hasnt finished immediately. The sender must stop retransmitting the request upon reception of a provisional response.

100 Trying
180 Ringing
181 Call is Being Forwarded
182 Queued
183 Session in Progress199 Early Dialog Terminated

2xx—Successful Responses

final responses express result of the processing of the associated request and they terminate the transactions.

200 OK
202 Accepted
204 No Notification

3xx—Redirection Responses

redirection response gives information about the user’s new location or an alternative service that the caller should try for the call. Used for cases when the server cant satisfy the call and wants the caller to try elsewhere . After this the caller is suppose to resend the request to the new location.

300 Multiple Choices
301 Moved Permanently
302 Moved Temporarily
305 Use Proxy
380 Alternative Service

4xx—Client Failure Responses

negative final responses indicating that the request couldn’t be processed  due to callers fault , for reasons such as t contains bad syntax or cannot be fulfilled at that server.

400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Conditional Request Failed
413 Request Entity Too Large
414 Request-URI Too Long
415 Unsupported Media Type
416 Unsupported URI Scheme
417 Unknown Resource-Priority
420 Bad Extension
421 Extension Required
422 Session Interval Too Small
423 Interval Too Brief
424 Bad Location Information
428 Use Identity Header
429 Provide Referrer Identity
430 Flow Failed
433 Anonymity Disallowed
436 Bad Identity-Info
437 Unsupported Certificate
438 Invalid Identity Header
439 First Hop Lacks Outbound Support
470 Consent Needed
480 Temporarily Unavailable
481 Call/Transaction Does Not Exist
482 Loop Detected.
483 Too Many Hops
484 Address Incomplete
485 Ambiguous
486 Busy Here
487 Request Terminated
488 Not Acceptable Here
489 Bad Event
491 Request Pending
493 Undecipherable
494 Security Agreement Required

5xx—Server Failure Responses

negative responses but indicating that fault is at server’s side for cases such as server cant or doesnt want to respond the the request.

500 Server Internal Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Server Time-out
505 Version Not Supported
513 Message Too Large
580 Precondition Failure

6xx—Global Failure Responses

request cannot be fulfilled at any server with definitive information

600 Busy Everywhere
603 Decline
604 Does Not Exist Anywhere
606 Not Acceptable

Mandatory Headers in SIP Response 
  • SIP/2.0 200 OK
  • Via: SIP/2.0/UDP host.domain.com:5060
  • From: Bob<sip:bob@domain.com>
  • To: Altanai<sip:altanai@domain.com>
  • Call-ID: 163784@host.domain.com
  • CSeq: 1 INVITE

Via, From, To, Call-ID , and  CSeq  

are copied exactly from Request. 

You can read more about SIP based Architecture here :SIP based architecture

Re-INVITE and Target-Refresh Request Handling in the Session Initiation Protocol (SIP)

An INVITE request sent within an existing dialog is known as a re-INVITE.
A re-Invite has an offer-answer exchange and can be used to

change the session and/or dialog params
change the port to which media should be sent.
change the connection address or media type.
Hold/Release and SUSPEND/RESUME rtp streams (connection address is zero).
FAX (T.38 and Bypass).

Re-INVITE with SDP useCases

  1. UAS rejects all changes in params in re-INVITE

Situtaion where UAC establishes audio only call
SDP1: m=audio 30000 RTP/AVP 0

but later wants to upgrade to video as well
SDP:m=audio 30000 RTP/AVP 0
m=video 30002 RTP/AVP 31

UAS configured to reject video streams, can reject this with a 4XX error and get ACK .
No changes to session are made

  1. UAS receives re-INVITE for param but wants to accept few and reject others, it sends back SDP with acceptable changes with 200 OK

For instance UAC moves to high bandwidth access point and wants to update IP of media stream . It also wanst to add video stream

initial SDP
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.1

new SDP in reINVITE
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.2
m=video 30002 RTP/AVP 31
c=IN IP4 192.0.2.2

UAS returns a 200 (OK) response to accept IP but sets the port of the video stream to zero in its SDP to show rejected of video stream.

m=audio 31000 RTP/AVP 0
c=IN IP4 192.0.2.5
m=video 0 RTP/AVP 31

another example is when UAC wwants to add anotehr audio codec and also add video stream to session

orignal SDP
m=audio 30000 RTP/AVP 0
c=IN IP4 192.0.2.1

re-invite SDP
m=audio 30000 RTP/AVP 0 3
c=IN IP4 192.0.2.1
m=video 30002 RTP/AVP 31
c=IN IP4 192.0.2.1

again the UAS will optionally accept the some param canges like audio code but set video to null IP address

m=audio 31000 RTP/AVP 0 3
c=IN IP4 192.0.2.5
m=video 31002 RTP/AVP 31
c=IN IP4 0.0.0.0

  1. UAS receives re-INVITE but wants for user intervention

UAS receives re-INVITE to add video , but instead of rejecting , it prompts user to permit.

So UAS provides a null IPaddress instead of setting the stream to ‘inactive’ because inactive streams still need to exchange RTP Control Protocol (RTCP) traffic
m=audio 31000 RTP/AVP 0
c=IN IP4 192.0.2.5
m=video 31002 RTP/AVP 31
c=IN IP4 0.0.0.0

Later if user rejects the addition of the video stream. Consequently, the UAS sends an UPDATE request (6) setting the port of the video stream to zero in its offer.
m=audio 31000 RTP/AVP 0
c=IN IP4 192.0.2.5
m=video 0 RTP/AVP 31
c=IN IP4 0.0.0.0

Ref:
RFC 6141 Updates the RFC 3261 with respect to re-INVITE and UAS behaviour
https://tools.ietf.org/html/rfc6141

Kamailio Transaction Module

Although most of kamailio module related description is covered here , I wanted to keep a separate space to describe and explain how kamailio handles transactions and in particular , Transaction Module .

Note : This article has been updated many time to match v5.1 since v3.0 from when it was written, if u see and outdated content or deprecated functions, please point them out to me in comments.

If you are new to kamailio , this post os not for you , instead read more on kamailio as a powerful sip server here or its application in telephony domain here .

Kamailio is basically only a transaction stateful proxy, without any dialog support build in. Here the TM module enables stateful processing of SIP transactions ( by maintaining state machine). State is a requirement for many complex logic such as accounting, forking , DNS resolution .

we know that SIP is a transactional protocol and every request and its response goes within a transaction. more on SIP as protocol is here

t_relay, t_relay_to_udp and t_relay_to_tcp are main functions to setup transaction state, absorb retransmissions from upstream, generate downstream retransmissions and correlate replies to requests.

Lifecycle of Transaction

Transactions lifecycle are controlled by various factors which includes coming from reliable ( TCP) or non reliable transport , invite or non invite transaction types etc.

Transaction are terminated either by final response or when timers are fired which control it.

Memory Management in Transactions

Transaction Module copies clones of received SIP messages in shared memory. non-TM functions operate over the received message in private memory. Therefore core operations ( like record_route) should not be called before settings the transaction state ( t_realy ) for state-fully processing a message.

An INVITE transaction will be kept in memory for maximum: max_inv_lifetime + fr_timer + wt_timer.
While A non-INVITE transaction will be kept in memory for a maximum: max_noninv_lifetime + wt_timer.

Branches

A single SIP INVITE request may be forked to multiple destinations , all of which together is called destination setse and Individual elements within the destination sets are called branches.

Serial , Parallel and Combined Forking – By default kamailio performs parallel forking sending msg to all destinations and waiting for response , however it can also do serail ie send request one by one and wait for reposne /timeout before sending next . By use of priorities ( q valaue 0 – 1.0), Kamailio can also intermix the forking technique ie decreasing priority oder for serial and same level for parallel . The destination uri are loaded using unctions t_load_contacts() and t_next_contacts().

parallel forking exmaple

request_route {
  seturi("sip:a@example.com");
  append_branch("sip:b@example.com");
  append_branch("sip:c@example.com");
  append_branch("sip:d@example.com");

  t_relay();
  break;
}

mixed forking exmaple

modparam("tm", "contacts_avp", "tm_contacts");
modparam("tm", "contact_flows_avp", "tm_contact_flows");

request_route {
  seturi("sip:a@example.com"); // lowest 0 
  append_branch("sip:b@example.com", "0.5"); // shoudl be in parallel with C
  append_branch("sip:c@example.com", "0.5"); // shoudl be in parallel with B
  append_branch("sip:d@example.com", "1.0"); // highest priority , should be tried first

  t_load_contacts();   // load all branches as per q values, store them in AVP configured in modparam 
  t_next_contacts();   // takes AVP and extracts higher q value branch

  t_relay();
  break;
}

Code to terminate when no more branches are found ( -1 returned) and return the message upstream

 ```
 failure_route["serial"]
 {
   if (!t_next_contacts()) {
     exit;
   }
t_on_failure("serial");
   t_relay();
 }
 ``

Transaction Module Parameters

various parameters are used to fine tune how trsnactions are handled and timedout in kamailio. Note all timers are set in miliseconds notation.

fr_timer (integer) – timer hit when no final reply for a request or ACK for a negative INVITE reply arrives. Default 30000 ms (30 seconds).

fr_inv_timer (integer) – timer hit when no final reply for an INVITE arrives after a provisional message was received on branch. Default 120000 ms (120 seconds).

restart_fr_on_each_reply (integer) – restart fr_inv_timer fir INVITE transaction for each provisional reply. Otherwise it will be sreatred only for fisrt and then increasing provisonal replies. Turn it off in cases when dealing with bad UAs that continuously retransmit 180s, not allowing the transaction to timeout.

max_inv_lifetime (integer) – Maximum time an INVITE transaction is allowed to be active in a tansaction. It starts from the time trnsaction was created and after this timer is hit , transaction is moved to either wait state or in the final response retransmission state. Default 180000 ms (180 seconds )

max_noninv_lifetime (integer) – Maximum time a non-INVITE transaction is allowed to be active. default 32000 ms (32 seconds )

wt_timer (integer) – Time for which a transaction stays in memory to absorb delayed messages after it completed.

delete_timer (integer) – Time after which a to-be-deleted transaction currently ref-ed by a process will be tried to be deleted again. This is now obsolte and now transaction is deleted the moment it’s not referenced anymore.

retr_timer1 (integer) – Initial retransmission period

retr_timer2 (integer) – Maximum retransmission period started increasingly from starts with retr_timer1 and stays constant after this

noisy_ctimer (integer) – if set, INVITE transactions that time-out (FR INV timer) will be always replied. Otherwise they will be quitely dropped without any 408 branch timeout resposne

auto_inv_100 (integer) – automatically send and 100 reply to INVITEs.

auto_inv_100_reason (string) – Set reason text of the automatically sent 100 to an INVITE.

unix_tx_timeout (integer) – nix socket transmission timeout,

aggregate_challenges (integer) – if more than one branch received a 401 or 407 as final response, then all the WWW-Authenticate and Proxy-Authenticate headers from all the 401 and 407 replies will be aggregated in a new final response.

blst_503 (integer) – reparse_invite=1.

blst_503_def_timeout (integer) – blacklist interval if no “Retry-After” header is present

blst_503_min_timeout / blst_503_max_timeout (integer) – minimum and maximun blacklist interval respectively

blst_methods_add (unsigned integer) – Bitmap of method types that trigger blacklisting on transaction timeouts and by default INVITE triggers blacklisting only

blst_methods_lookup (unsigned integer) – Bitmap of method types that are looked-up in the blacklist before being forwarded statefully. For default only applied to BYE.

reparse_invite (integer) – set if CANCEL and negative ACK requests are to be constructed from the INVITE message ( same record-set etc as INVITE ) which was sent out instead of building them from the received request.

ac_extra_hdrs (string) – Header fields prefixed by this parameter value are included in the CANCEL and negative ACK messages if they were present in the outgoing INVITE. Can be only used with reparse_invite=1.

reparse_on_dns_failover (integer) – SIP message after a DNS failover is constructed from the outgoing message buffer of the failed branch instead of from the received request.

on_sl_reply (string) – Sets reply route block, to which control is passed when a reply is received that has no associated transaction.

modparam("tm", "on_sl_reply", "stateless_replies")
...
onreply_route["stateless_replies"] {
    // return 0 if do not allow stateless replies to be forwarded
    return 1; // will pass to core for stateless forwading
}

xavp_contact (string) – name of XAVP storing the attributes per contact.

contacts_avp (string) – name of an XAVP that stores names of destination sets. Used by t_load_contacts() and t_next_contacts() for forking branches

contact_flows_avp (string) – name of an XAVP that were skipped

fr_timer_avp (string) – override teh value of fr_timer on per transactio basis , outdated

fr_inv_timer_avp (string) – same as abovel , outdated

cancel_b_method (integer) – method to CANCEL an unreplied transaction branch. Params :
0 will immediately stop the request (INVITE) retransmission on the branch so that unrpelied branches will be terminated
1 will keep retransmitting the request on unreplied branches.
2 end and retransmit CANCEL even on unreplied branches, stopping the request retransmissions.

unmatched_cancel (string) – sets how to forward CANCELs that do not match any transaction. Params :
0 statefully
1 statelessly
2 dropping them

ruri_matching (integer) – try to match the request URI when doing SIP 1.0 transaction matching as older SIP didnt have via cookies as in RFC 3261

via1_matching (integer) – match the topmost “Via” header when doing SIP 1.0 transaction matching

callid_matching (integer) – match the callid when doing transaction matching.

pass_provisional_replies (integer)

default_code (integer) – Default response code sent by t_reply() ( 500 )

default_reason (string) – Default SIP reason phrase sent by t_reply() ( “Server Internal Error” )

disable_6xx_block (integer)- treat all the 6xx replies like normal replies. However according to RFC receiving a 6xx will cancel all the running parallel branches, will stop DNS failover and forking.

local_ack_mode (integer) – where locally generated ACKs for 2xx replies to local transactions are sent. Params :
0 – the ACK destination is choosen according next hop in contact and the route set and then DNS resolution is used on it
1 – the ACK is sent to the same address as the corresponding INVITE branch
2 – the ACK is sent to the source of the 2xx reply.

failure_reply_mode (integer) – how branches are managed and replies are selected for failure_route handling. Params :
0 – all branches are kept
1 – all branches are discarded
2 – only the branches of previous leg of serial forking are discarded
3 – all previous branches are discarded
if you dont want to drop all branches then use t_drop_replies() to sleectively drop

faked_reply_prio (integer) – how branch selection is done.

local_cancel_reason (boolean) – add reason headers for CANCELs generated due to receiving a final reply.

e2e_cancel_reason (boolean) – add reason headers for CANCELs generated due to receiving a CANCEL

remap_503_500 (boolean) – conversion of 503 response code to 500. RFC requirnment.

failure_exec_mode (boolean) – Add local failed branches in timer to be considered for failure routing blocks.

dns_reuse_rcv_socket (boolean) – reuse of the receive socket for additional branches added by DNS failover.

event_callback (str) – function in the kemi configuration file (embedded scripting language such as Lua, Python, …) to be executed instead of event_route[tm:local-request] block. The function recives a string param with name of the event

modparam("tm", "event_callback", "ksr_tm_event")
...
function ksr_tm_event(evname)
    KSR.info("===== TM module triggered event: " .. evname .. "\n");
    return 1;
end

relay_100 (str) – whether or not a SIP 100 response is proxied. not valid behavior when operating in stateful mode and only useful when in stateless mode

rich_redirect (int) – to add branch info in 3xx class reply. Params :
0 – no extra info is added (default)
1 – include branch flags as contact header parameter
2 – include path as contact uri Route header

RCS ( Rich Communication Suite )

What is this fuss about RCS ? For the past few weeks I’ve been trying to find the answer to this one .

After much information gathering i made myself understand that  :-

The Rich Communication Services programme is a global initiative to deploy inter-operator services within an industry ecosystem.

Marketed by the GSMA under the brand name joyn,  RCS is an upgrade that marks the transition of messaging and voice capabilities from Circuit Switched technology to an all-IP world.

Wider and large scale IMS deployment, interoperability between different terminal vendor RCS clients and RCS service interworking between operators are the key aims of the RCS Initiative.

Whats special about RCS ?

  • Enhanced Phonebook: service capabilities and enhanced contacts information such as presence and service discovery.
  • Enhanced Messaging: enables a large variety of messaging options including chat, emoticons, location share and file sharing.
  • Enriched Calls: enables multimedia content sharing during a voice call, video call and video sharing (see what I see).

RCS releases

Five releases of the RCS specifications have been made to date. Each release expanded the scope of its predecessor.

lRelease 1 : Offered the first definitions for the enrichment of voice and chat with content sharing, driven from an RCS enhanced address book.
lRelease 2 : Added broadband access to RCS features: enhancing the messaging and enabling sharing of files.
lRelease 3: Focused on the broadband device as a primary device.
lRelease 4: Included support for LTE.
lRelease 5: The most recent release, global interoperability is a key aspect of these specifications.
……………………………………………………………………………..

As the team developed a web client for making and receiving SIP calls over websockets through a proxy SIP server , I felt its an  achievement big enough. To integrate it with RCS ( Rich Communication Suite ) stack appeared as a very complicated job .

I began by adding RCS specific standards modules one by one instead of importing the whole stack / library all together  .

So the modules for XCAP for buddylist  , MSRP for file transfer , geolocation  mapping , cloud sync of phonebook and message book have begun taking shape . In essence following features set are expected out of a RCS enabled Client  ( short outline )

Provisioning

  • · OAUTH integration with operator customer portal
  • · RCS HTTP Auto-Configuration 
  • · Manual IMS credentials, typically reserved for testing / troubleshooting RCS Services

RCS services:

  • · Service Discovery
    • OPTIONS and Presence supported
    • Address book polling
  • · 1-1 Chat
    • IMDN
    • Is-Composing
    • Store & forward / deferred message and notification delivery
    • Hotfixes compliant
  • · Group Chat
    • Hotfixes compliant
    • Is-Composing
    • IMDN
    • Geo-location Push
  • · File Transfer
    • MSRP based
    • HTTP based
    • Store & forward
    • Geo-location push via FT
    • vCard sharing
    • Thumbnail support
  • · Voice & video
    • Best effort voice
    • Transcode 
  • · Network Address Book Support
    • Synchronization to SyncML based network address book
    • Contact import from Google, Facebook etc.

…………………………………………………………………………………………………..

At this stage i will also put in a bit more about RCS e

RCS e

What is the difference between RCS-e and RCS?

RCS-enhanced (RCS-e) is the currently available version of RCS, developed to speed time to market. It offers enhanced features such as instant messaging, live video sharing, and file transfer across any device on any network operator.

RCS e Benefits :

Focus on advanced communication
– chat , file transfer , video sharing
Easy to Use
-zero touch from end user perspective
-minimal setup for subscribers
-Interoperability across devices , infrastructure components and service providers
Low barrier to entry / simplify networks
– Capability discovery using SIP OPTIONS
– Less impact on network elements and handset battery
– Lack of presence server reduces cost and time to market
Universal
– Allows implementation in lower range devices
– One common device specification

RCS-e Customer Value Proposition

 New IP Communication Services , Profile Sharing , Native Device Integration
rcs5 rcs6

RCS e Characteristics

Dynamic Capability Discovery
User Perspective
network detects when user attaches with RCs e device
detection triggers network provisioning and client configuration
authentication by network
SSO / GIBA in 3G coverage
SIP Digest in Wifi
Encryption for Wifi access
TLS for SIP and TCP media or IPsec
SRTP for UDP or IPsec
NAT traversal and Keep-alives
…………………………………………………………………………………………..

JAINSLEE – Developer and business benefits

JAIN SLEE is the Java open standard for a SLEE ( Service Logic Execution Environment ). It is a  Java programming language API for developing and deploying network services.

DukeJAINSLEE

 Evolution of Open- Standard Platform (JAINSLEE)

There is a strong evolution being seen in CSP space. Now operators are looking forward to implement the open standard for intelligent networks. It reduces their dependency on proprietary platforms and on vendor’s road maps. Open –source platform gives operator flexibility to develop their own applications without being dependent on vendor. An open, standards based, service logic execution environment (SLEE) that integrates with current and future networks is the key to providing innovative and revenue generating services. Providing one (standards based) carrier grade execution environment that integrates SS7, SIP, OSA/Parlay, OSS/BSS and J2EE environments offers significant benefits to operator.

Business benefits of SIP JAINSLEE based platform

  1. Network Independence: The JAIN SLEE framework is independent of any particular network protocol, API or network topology. This is supported through the resource adaptor architecture
  2. Portable Services: Application components can be developed and then deployed on JAIN SLEE compliant platforms from different vendors without recompilation or source code modification.
  3. Supports Complex Applications: JAIN SLEE application components can have state, can be composed from other components, can create and destroy other application components, can invoke other application components both synchronously and asynchronously, and can invoke resource adaptors.
  4. Industry Standard: JAIN SLEE is specified via the Java Community Process which allows multiple companies and individuals to collaborate in developing Java technology specifications.
  5. In order to reduce the operating cost of legacy infrastructure more and more operators are investing and implementing open source platform. These new platforms bring agility and new service delivery capability to CSP.
  6. The JAINSLEE based platform can be used to develop and deploy carrier-grade applications that use SS7-based protocols such as INAP and CAP, IP protocols such as SIP and Diameter, and IT / Web protocols, such as HTTP Servlet, XML and Service Orientated Architectures (SOA).

Fundamental Concepts :

  • Application can be written once and run on many different implementations of JAIN SLEE.
  • Applications can access resources and protocols across multiple networks from within the JAIN SLEE environment.
  • Follows the ACID transaction .
  • component model for structuring the application logic of communications applications as a collection of reusable
  • object-orientated components, and for  composing these components into higher level and more sophisticated services.
  • SLEE specification also defines the management interfaces used to administer the application environment and also
  • defines set of standard Facilities (such as the Timer Facility, Trace Facility, and Alarm Facility so on  )
  •  Extension framework to allow new external protocols and systems (such as MSCs, MMSCs, SMSCs, Softswitchs, CSCFs, HLRs) to be integrated.

Characteristics of SLEE specification

• Event based model, asynchronous, support for composition

• Container manages component state

• Container manages garbage collection of components

• Transaction boundaries for demarcation and semantics of state replication

• Strongly typed event handling signatures

• 3rd party event driven components

• Management of lifecycle of Server, Services, Provisioned state

• Versioned services, upgrade of services, existing activities stay on existing service instances, new activities are directed to instances of upgraded services

• Independent of network technology/ protocols/elements through resource adaptor architecture

Entities :

jianslee environment

Service

A service in JAIN SLEE terminology is a managed field replaceable unit.

The system administrator of a JAIN SLEE controls the life cycle (including deployment, undeployment and on-line upgrade) of a service. The program code can include Java classes Profiles, and Service Building Blocks.

Profile

A JAIN SLEE Profi le contains provisioned service or subscriber data.

Service Building Blocks running inside the JAINSLEE may access profiles as part of their application logic.

Service Building Block

The element of re-use defined by JAINSLEE is the Service Building Block (SBB).

An SBB is a software component that sends and receives events and performs computational logic based on the receipt of events and its current state. SBBs are stateful.

The program code for an SBB is comprised of Java classes.

Event

An event represents an occurrence that may require application processing.

An event may originate from a number of different sources, for example, an external resource such as a communications protocol stack, from the SLEE itself, or from application components within the SLEE.

Resources and Resource ADAPTERS

Resources are external entities that interact with other systems outside of the SLEE, such as network elements (HLR, MSC, etc), protocol stacks, directories and databases.

A Resource Adaptor implements the interfacing of a Resource into the JAINSLEE environment.


JAIN SLEE

•Jain SLEE :- JAIN is a Sun Java standards initiative and part of the Java Community Process.
JAIN specifies a comprehensive range of APIs that target converged IP and PSTN networks, including APIs for

– High-level application development (such as service provider APIs and the Service Logic Execution Environment (SLEE))

– call control

– signalling at the protocol level (such as SIP, MGCP and SS7)

•For telephony, data and wireless communications networks, the Java APIs defined through.

– service portability

– network independence

– open development

•A Service Logic Execution Environment (SLEE) is high-throughput, low-latency, event-processing application environment.
•JAIN SLEE  is designed specifically to allow implementations of a standard to meet the stringent requirements of communications applications (such as network-signaling applications).

Goals of JAIN SLEE are:

– Portable services and network independence.

– Hosting on an extensible platform.

– services and SLEE platform available from many vendors.

Key Features are  :

•Industry standard :- JSLEE is the industry-agreed standard for an application server that meets the specific needs of telecommunications networks.
•Network independence:-The JSLEE programming model enables network independence for the application developer. The model is independent of any particular network protocol, API or network topology.
•Converged services:- JSLEE provides the means to create genuinely converged services, which can run across multiple network technologies.
•Network migrations :-As JSLEE provides a generic, horizontal platform across many protocols, independent of the network technology, it provides the ideal enabler technology for smooth transition between networks.
•Global market—global services:-JSLEE-compliant applications, hosted on a JSLEE application server are network agnostic. A single platform can be used across disparate networks
•Robust and reliable:- As with the enterprise application server space, deploying applications on a standard application server that has been tested and deployed in many other networks reduces logic errors, and produces more reliable applications
•Standard object orientated component  architecture

Scope of JAINSLEE applications

•The principal features of the JSLEE programming model are :

– programs written in Java

-asynchronous programming paradigm

-well-defined event-delivery semantics

-component-based, object-oriented approach

-transactional model

-“profiles” of information, which represent provisioned data

-usage interfaces that support gathering service statistics

-support for standard Java APIs (such as JNDI and JDBC), and optionally, support integration with J2EE

-standard facilities for traces, alarms and timers, for use by the applications that are hosted on the SLEE

Resource adaptors

-The JSLEE provides integration capabilities using a plug-in architecture known as the resource adapter

architecture. Resource adaptors (RAs) provide interconnection with the “outside” world, for example,

interfaces to communication protocol stacks, directory services or external systems.

•SLEE management

-The JSLEE specification also defines the management capabilities of the SLEE. It adopts the Java standard

in this area, Java for Management Extensions (JMX).

————————————————————————————————————————

SIP VoIP system Architecture

Updated on Jan 2017


SIP solutioning and architectures  is a subsequent article after SIP introduction, which can be found here.

A VOIP Solution is designed to accommodate the signalling and media both along with integration leads to various external endpoints such as various SIP phones ( desktop, softphones , webRTC ) ,  telecom carriers  , different voip network providers  , enterprise applications  ( Skype , Microsoft Lync  ), Trunks etc .

A sufficiently capable SIP platform should consist of following features :

  • audio calls ( optionally video )
  • media services such as conferencing, voicemail, and IVR,
  • messaging as IM and presence based on SIMPLE,
  • programmable services through standardized APIs and development of new modules
  • near-end and far-end NAT traversal for signalling and media flows
  • interconnectivity with other IP multimedia systems, VoLTE ( optional interconnection with other types of communications networks as GSM or PSTN/ISDN)
  • registry , location and lookup service
  • Backend support like Redis, MySQL, PostgreSQL, Oracle, Radius, LDAP, Diameter
  • serial and parallel forking
  • support for Voip signalling protocols (SIP, H,323, SCCP, MGCP, IAX) and telephony signalling protocols ( ISDN/SS7, FXS/FXO, Sigtran ) either internally via pluggable modules or externally via gateways

Performnace factors :

  • High availability using redundant servers in standby
  • Load balancing
  • IPv4 and IPv6 network layer support
  • TCP , UDP , SCTP transport layer protocol support
  • DNS lookups and hop by hop connectvity

Security considerations :

  • authentication, authorization, and accounting (AAA)
  • Digest authentication and credentials fetched from backend
  • Media Encryption
  • TLS and SRTP support
  • Topology hidding to prevent disclosing IP form internal components in via and route headers
  • Firewalls , blacklist, filters , peak detectors to prevent Dos and Ddos attacks

The article only outlines SIP system architecture  from 3 viewpoints :

  • from Infrastructure standpoint
  • from core voice engineering perspective
  • and accompanying external components required to run and system

Infrastructure Requirements

  • Data Centers with BCP ( Business Continuity Planning ) and DR ( Disaster Recovery )
  • Servers and Clusters for faster and parallel calculating
  • Virtualization
    VMs to make a distributed computing environment with HA ( high availability ) and DRS ( Distributed Resource Scheduling )
  • Storage
    SAN with built in redundancy for resiliency of data.
    WORM compliant NAS for storing voice archives over a retention period.
  • Racks, power supplies, battery backups, cages etc.
  • Networking
    DMZs ( Demilitarised Zones)  which are interfacing areas between internal servers in green zone and outside network
    VLANs for segregation between tenants.
    Connectivity through the public Internet as well as through VPN or dedicated optical fibre network for security.
  • Firewall configuration
  • Load Balancer ( Layer 7 )
  • Reverse Proxies for security of internal IPs and port
  • Security controls In compliance with ISO/IEC 27000 family – Information security management systems
  • PKI Infrastructure to manage digital certificates
  • Key management with HSM ( hardware security Module )
  • truster CA ( Certificate Authority ) to issue publicly signed certificate for TLS ( Https , wss etc)
  • OWASP ( Open Web Application Security Project )  rules compliance

Integral Components of a VOIP SIP based architecture

sip entities
SIP platform components
  • Call Controller
  • Media Manager
  • Recording
  • Softclients
  • logs and PCAP archives
  • CDR generators
  • Session Borer Controllers ( SBCs)

Detailing some of the protocols apart from SIP used in VOIP solution

RTP ( Real Time Transport Protocol )

RTP handles realtime multimedia transport between end to end network components . RFC 3550 .

Image result for RTP packet structure

Packet structure of RTP     

RTP Header contain timestamp , name of media source , codec type and sequence number .

Image result for RTP header structure

RTCP

– tbd

DTMF( Dual tone Multi Frequency )

delivery options:

  • Inband –  With Inband digits are passed along just like the rest of your voice as normal audio tones with no special coding or markers using the same codec as your voice does and are generated by your phone.
  • Outband  – Incoming stream delivers DTMF signals out-of-audio using either SIP-INFO or RFC-2833 mechanism, independently of codecs – in this case the DTMF signals are sent separately from the actual audio stream.

Types of SIP servers are listed below . It is important to understand the roles a SIP server can be moulded to take up which in turn defines its placement in overall voip communication platform such as stateless proxy servers on the border , application and B2BUA server at the core etc

SIP Gateways:

A SIP gateway is an application that interfaces a SIP network to a network utilising another signalling protocol. In terms of the SIP protocol, a gateway is just a special type of user agent, where the user agent acts on behalf of another protocol rather than a human. A gateway terminates the signalling path and can also terminate the media path .

sip gaeways

To PSTN for telephony inter-working
To H.323 for IP Telephony inter-working
Client – originates message
Server – responds to or forwards message

Logical SIP entities are:

User Agent Client (UAC): Initiates SIP requests  ….
User Agent Server (UAS): Returns SIP responses ….
Network Servers ….

Registrar Server

A registrar server accepts SIP REGISTER requests; all other requests receive a 501 Not Implemented response. The contact information from the request is then made available to other SIP servers within the same administrative domain, such as proxies and redirect servers. In a registration request, the To header field contains the name of the resource being registered, and the Contact header fields contain the contact or device URIs.

regsitrar server

Proxy Server

A SIP proxy server receives a SIP request from a user agent or another proxy and acts on behalf of the user agent in forwarding or responding to the request. Just as a router forwards IP packets at the IP layer, a SIP proxy forwards SIP messages at the application layer.

Typically proxy server ( inbound or outbound) have no media capabilities and ignore the SDP . They are mostly bypassed once dialog is established but can add a record-route .
A proxy server usually also has access to a database or a location service to aid it in processing the request (determining the next hop).

proxy server

 1. Stateless Proxy Server
A proxy server can be either stateless or stateful. A stateless proxy server processes each SIP request or response based solely on the message contents. Once the message has been parsed, processed, and forwarded or responded to, no information (such as dialog information) about the message is stored. A stateless proxy never retransmits a message, and does not use any SIP timers

2. Stateful Proxy Server
A stateful proxy server keeps track of requests and responses received in the past, and uses that information in processing future requests and responses. For example, a stateful proxy server starts a timer when a request is forwarded. If no response to the request is received within the timer period, the proxy will retransmit the request, relieving the user agent of this task.

  3 . Forking Proxy Server
A proxy server that receives an INVITE request, then forwards it to a number of locations at the same time, or forks the request. This forking proxy server keeps track of each of the outstanding requests and the response. This is useful if the location service or database lookup returns multiple possible locations for the called party that need to be tried.

Redirect Server

A redirect server is a type of SIP server that responds to, but does not forward, requests. Like a proxy server, a redirect server uses a database or location service to lookup a user. The location information, however, is sent back to the caller in a redirection class response (3xx), which, after the ACK, concludes the transaction. Contact header in response indicates where request should be tried .

redirect server

Application Server

The heart of all call routing setup. It loads and executes scripts for call handling at runtime and maintains transaction states and dialogs for all ongoing calls . Usually the one to rewrite SIP packets adding media relay servers, NAT . Also connects external services like Accounting , CDR , stats to calls .

Developing SIP based applications

Basic SIP methods

SIP defines basic methods such as INVITE, ACK and BYE which can pretty much handle simple call routing with some more advanced processoes too like call forwarding/redirection, call hold with optional Music on hold, call parking, forking, barge etc.

Extending SIP headers

Newer SIP headers defined by more updated SIP RFC’s contina INFO, PRACK, PUBLISH, SUBSCRIBY, NOTIFY, MESSAGE, REFER, UPDATE. But more methods or headers can be added to baseline SIP packets for customization specific to a particular service provider. In case where a unrecognized SIP header is found on a SIP proxy which it either does not suppirt or doesnt understand, it will simply forward it to the specified endpoint.

Call routing Scripts

Interfaces for programming SIP call routing include :
– Call Processing Language—SIP CPL,
– Common Gateway Interface—SIP CGI,
– SIP Servlets,
– Java API for Integrated Networks—JAIN APIs etc .

Some known SIP stacks
– SailFin – SIP servlet container uses GlassFish open source enterprise Application Server platform (GPLv2), obsolete since merger from Sun Java to Oracle.
– Mobicents – supports both JSLEE 1.1 and SIP Servlets 1.1 (GPLv2)
– Cipango – extension of SIP Servlets to the Jetty HTTP Servlet engine thus compliant with both SIP Servlets 1.1 and HTTP Servlets 2.5 standards.
– WeSIP – SIP and HTTP ( J2EE) converged application server build on OpenSER SIP platform

Additionally SIP stacks are supported on almost all popular SIP programming lanaguges which can be imported as lib as used for building call routing scripts to be mounted on SIP servers or endpoints such as :
– PJSIP in C
– JSSIP Javascript
– Sofia in kamailio

Some popular SIP server also have proprietary scripting language such as
Asterisk Gateway Interface (AGI) , application interface for extending the dialplan with your functionality in the language you choose – PHP, Perl, C, Java, Unix Shell and others

Adding Media Management

Media processing is usually provided by media servers in accordance to the SIP signalling. Brideges, call recording, Voicemail, audio conferencing, and interactive voice response (IVR) are commomly used.
RFC 6230 Media Control Channel Framework decribes framework and protocol for application deployment where the application programming logic and media processing are distributed

Any one such service could be a combination of many smaller services within such as Voicemail is a combitional of prompt playback, runtime controls, Dual-Tone Multi-Frequency (DTMF) collection, and media recording. RFC 6231 Interactive Voice Response (IVR) Control Package for the Media Control Channel Framework.

SIP platform Development

A sufficiently capable SIP platform shoudl consist of following features :

  • audio calls ( optionally video )
  • media services such as conferencing, voicemail, and IVR,
  • messaging as IM and presence based on SIMPLE,
  • programmable services through standardized APIs and development of new modules
  • near-end and far-end NAT traversal for signalling and media flows
  • interconnectivity with other IP multimedia systems, VoLTE ( optional interconnection with other types of communications networks as GSM or PSTN/ISDN)
  • registry , location and lookup service
  • serial and parallel forking

Performance factors :

  • High availability using redundant servers in standby
  • Load balancing
  • IPv4 and IPv6 support

Security considerations :

  • digest authentication and credentials fetched from backend
  • Media Encryption
  • TLS and SRTP support
  • Topology hiding to prevent disclosng IP form internal components in via and route headers
  • Firewalls , blacklist, filters , peak detectors to prevent Dos and Ddos attacks

Add NAT and DNS components

To adapt SIP to modern IP networks with inter network traversal ICE, far and near-end NAT traversal solutions are used. Network Address traversal is crtical to traffic flow between private public network and from behind firewalls and policy controlled networks
One can use any of the VOVIDA-based STUN server, mySTUN , TurnServer, reStund , CoTURN , NATH (PJSIP NAT Helper), ReTURN, or ice4j

Near-end NAT traversal

STUN (session traversal utilities for NAT) – UA itself detect presence of a NAT and learn the public IP address and port assigned using Nating. Then it replaces device local private IP address with it in the SIP and SDP headers. Implemented via STUN, TURN, and ICE.
limitations are that STUN doesnt work for symmetric NAT (single connection has a different mapping with a different/randomly generated port) and also with situations when there are multiple addresses of a end point.

TURN (traversal using relay around NAT) or STUN relay – UA learns the public IP address of the TURN server and asks it to relay incoming packets. Limitatiosn since it handled all incoming and outgong traffic , it must scale to meet traffic requirments and should not become the bottle neck junction or single point of failure.

ICE (interactive connectivity establishment) – UA gathers “candidates of communication” with priorities offered by the remote party. After this client pairs local candidates with received peer candidates and performs offer-answer negotiating by trying connectivity of all pairs, therefore maximising success. The types of candidates :
– host candidate who represents clients’ IP addresses,
– server reflexive candidate for the address that has been resolved from STUN
– and a relayed candidate for the address which has been allocated from a TURN relay by the client.

Far-end NAT traversal

UA is not concerned about NAT at all and communicated using its local IP port. The border controller implies a NAT handling components such as an application layer gateway (ALG) or universal plug and play (UPnP) etc which resolves the private and public network address mapping by act as a back to back user agent (B2BUA).
Far end NAT can also be enabled by deploying a public SIP server which performs media relay (RTP Proxy/Media proxy).

Limitations of this approach
security risks as they are operating in public network
enabling reverse traffic from UAS to UAC behind NAT.

A keep-alive mechanism is used to keep NAT translations of communications between SIP endpoint and its serving SIP servers opened , so that this NAT translation can be reused for routing. It contains client-to-server “ping” keep-alive and corresponding server-to-client “pong” messages. The 2 keep-alive mechanisms: a CRLF keep-alive and a STUN keep-alive message exchange.

The 3 types of SIP URIs,

  • address of record (AOR)
  • fully qualified domain name (FQDN)
  • globally routable user agent (UA) URI
    SIP uniform resource identifiers (URIs) are identified based on DNS resolution since the URI after @ symbol contains hostname , port and protocl for the next hop.

Adding record route headers for locating the correct SIP server for a SIP message can be done by :
– DNS service record (DNS SRV)
– naming authority pointer (NAPTR) DNS resource record

Steps for SIP endpoints locating SIP server

  1. From SIP packet get the NAPTR record to get the protocl to be used
  2. Inspect SRV record to fetch port to use
  3. Inspect A/AAA record to get IPv4 or IPv6 addresses
    ref : RFC 3263 – Locating SIP Servers
    Can use BIND9 server for DNS resolution supports NAPTR/SRV, ENUM, DNSSEC, multidomains, and private trees or public trees.

Cross platform and integration to External Telecommunication provider landscape

connection to IMS such as openIMS
support for Voip signalling protocols (SIP, H,323, SCCP, MGCP, IAX) and telephony signalling protocls ( ISDN/SS7, FXS/FXO, Sigtran ) either internally via pluggable modules or externally via gateways

Database Integration

Need backend , cache , databse integration to npt only store routing rules with temporary varaible values but also account details , call records details, access control lists etc. Should therefore extend integartion with text based db, redis, MySQL, PostrgeSQL, OpenLDAP, and OpenRadius.

The obvious starting milestone before making a full scale carrier grade, SIP based VoIP system is to start by building a PBX for intra enterprise communication. There are readily available solutions to make a IP telephony PBX kamailio , freeswitch , asterisk , Elastix , SipXecs


There are other external components to setup a VOIP solution apart from Core voice Servers and gateways like the ones listed below, I will try to either add a detailed overall architecture diagram here or write about them in an seprate article . Keep watching this space for updates

  • Payment Gateways
  • Billing and Invoice
  • Fraud Prevention
  • Contacts Integration
  • Call Analytics
  • API services
  • Admin Module
  • Number Management ( DIDs ) and porting
  • Call Tracking
  • Single Sign On and User Account Management with Oauth and SAML
  • Dashboards and Reporting
  • Alert Management
  • Continuous Deployment
  • Automated Validation
  • Queue System
  • External cache