Due to its very flexible and customisable routing engine it can be used in number of scenarios such as an SIP proxy or a router and due to its high throughput it is widely recommended as an enterprise grade inbound/outbound proxy server.
This article talks about modules and subparts of Opensips and their role in defining the purpose and application of Opensips which can be as an lighweight proxy to loadbalancer or even as AAA server.
Dispatcher Module
This modules implements a dispatcher for destination addresses. It computes hashes over parts of the request and selects an address from a destination set. The selected address is used then as outbound proxy. The module can be used as a stateless load balancer, having no guarantee of fair distribution.
Path to the file with destination sets by default is “/etc/opensips/dispatcher.list” or “/usr/local/etc/opensips/dispatcher.list”.
setid_col (string) – storing the gateway’s group id. Default value is “setid”.
modparam("dispatcher", "setid_col", "groupid")
destination_col (string) – destination’s sip uri.
modparam("dispatcher", "destination_col", "uri")
flags_col (string) – The column’s name in the database storing the flags for destination uri.
modparam("dispatcher", "flags_col", "dstflags")
force_dst (int) – If set to 1, force overwriting of destination address when that is already set. Default value is “0”.
modparam("dispatcher", "force_dst", 1)
flags (int) – affect dispatcher’s behaviour. Default value is “0”.
If flag 1 is set only the username part of the uri will be used when computing an uri based hash.
If no flags are set the username, hostname and port will be used The port is used only if different from 5060 (normal sip uri) or 5061 (in the sips case).
If flag 2 is set, then the failover support is enabled. The functions exported by the module will store the rest of addresses from the destination set in AVP, and use these AVPs to contact next address when the current-tried fails.
modparam("dispatcher", "flags", 3)
use_default (int) – If the parameter is set to 1, the last address in destination set is used as last option to send the message. For example, it is good when wanting to send the call to an anouncement server saying: “the gateways are full, try later”. Default value is “0”.
modparam("dispatcher", "use_default", 1)
dst_avp (str) – The name of the avp which will hold the list with addresses, in the order they have been selected by the chosen algorithm.
modparam("dispatcher", "dst_avp", "$avp(i:271)")
If use_default is 1, the value of last dst_avp_id is the last address in destination set. The first dst_avp_id is the selected destinations. All the other addresses from the destination set will be added in the avp list to be able to implement serial forking.
grp_avp (str) – The name of the avp storing the group id of the destination set. Good to have it for later usage or checks. Default is null.
modparam("dispatcher", "grp_avp", "$avp(i:272)")
cnt_avp (str) – The name of the avp storing the number of destination addresses kept in dst_avp avps.
modparam("dispatcher", "cnt_avp", "$avp(i:273)")
hash_pvar (str) – String with PVs used for the hashing algorithm like to do hashing over custom message parts.Default value is “null” – disabled.
ds_ping_method (string) – With this Method you can define, with which method you want to probe the failed gateways. This method is only available, if compiled with the probing of failed gateways enabled. Default value is “OPTIONS”.
modparam("dispatcher", "ds_ping_method", "INFO")
ds_ping_from (string) – With this Method you can define the “From:”-Line for the request, sent to the failed gateways. This method is only available, if compiled with the probing of failed gateways enabled. Default value is “sip:dispatcher@localhost”.
ds_ping_interval (int – With this Method you can define the interval for sending a request to a failed gateway. This parameter is only used, when the TM-Module is loaded. If set to “0”, the pinging of failed requests is disabled.Default value is “10”.
modparam("dispatcher", "ds_ping_interval", 30)
ds_probing_threshhold (int) – If you want to set a gateway into probing mode, you will need a specific number of requests until it will change from “active” to probing. The number of attempts can be set with this parameter. Default value is “3”.
ds_probing_mode (int) – Controls what gateways are tested to see if they are reachable.
If set to 0, only the gateways with state PROBING are tested,
if set to 1, all gateways are tested. If set to 1 and the response is 407 (timeout), an active gateway is set to PROBING state. Default value is “0”.
modparam("dispatcher", "ds_probing_mode", 1)
options_reply_codes (str) – The codes defined here will be considered as valid reply codes for OPTIONS messages used for pinging, apart for 200. Default value is “NULL”.
ds_select_dst(set, alg) – The method selects a destination from addresses set. Algorithm used to select the destination address can be :
“0” – hash over callid
“1” – hash over from uri.
“2” – hash over to uri.
“3” – hash over request-uri.
“4” – round-robin (next destination).
“5” – hash over authorization-username (Proxy-Authorization or “normal” authorization). If no username is found, round robin is used.
“6” – random (using rand()).
“7” – hash over the content of PVs string. Note: This works only when the parameter hash_pvar is set.
“X” – if the algorithm is not implemented, the first entry in set is chosen.
ds_select_dst("1", "0");
You can use ‘ds_next_dst()’ to use next address to achieve serial forking to all possible destinations. This function can be used from REQUEST_ROUTE.
ds_select_domain(set, alg) – selects a destination from addresses set and rewrites the host and port from R-URI. This function can be used from REQUEST_ROUTE.
ds_next_dst() – Takes the next destination address from the AVPs with id ‘dst_avp_id’ and sets the dst_uri (outbound proxy address). This function can be used from FAILURE_ROUTE.
ds_next_domain() – Takes the next destination address from the AVPs with id ‘dst_avp_id’ and sets the domain part of the request uri. This function can be used from FAILURE_ROUTE.
ds_mark_dst() – Mark the last used address from destination set as inactive, in order to be ingnored in the future. In this way it can be implemented an automatic detection of failed gateways. When an address is marked as inactive, it will be ignored by ‘ds_select_dst’ and ‘ds_select_domain’. This function can be used from FAILURE_ROUTE.
ds_mark_dst(“s”) – Mark the last used address from destination set as :
inactive (“i”/”I”/”0”),
active (“a”/”A”/”1”) or
probing (“p”/”P”/”2”).
With this function, an automatic detection of failed gateways can be implemented. When an address is marked as inactive or probing, it will be ignored by ‘ds_select_dst’ and ‘ds_select_domain’.
ds_is_from_list() – This function returns true, if the current request comes from a host from the dispatcher-list; otherwise false. This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE and ONREPLY_ROUTE.
ds_is_from_list(“group”) – This function returns true, if the current request comes from a host in the given group of the dispatcher-list; otherwise false.
This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE and ONREPLY_ROUTE.
Exported MI Functions
ds_set_state – Sets the status for a destination address (can be use to mark the destination as active or inactive).
Parameters: state : state of the destination address
“a”: active
“i”: inactive
“p”: probing group: destination group id address: address of the destination in the group
MI FIFO Command Format:
:ds_set_state:reply_fifo_file state group address empty_line
ds_list – It lists the groups and included destinations.
MI FIFO Command Format:
:ds_list:reply_fifo_file empty_line
ds_reload – reloads the groups and included destinations.
MI DATAGRAM Command Format:
":ds_reload:\n."
Installation and Running
Destination List File – Each destination point must be on one line. First token is the set id, followed by destination address. Optionally, the third field can be flags value (1 – destination inactive, 2 – destination in probing mod — you can do bitwise OR to set both flags). The set id must be an integer value. Destination address must be a valid SIP URI. Empty lines or lines starting with “#” are ignored.
Exmaple of a dispatcher list file
line format
setit(integer) destination(sip uri) flags (integer, optional)
Implementation for a simplified database engine based on text files. It can be used by OpenSIPS DB interface instead of other database module (like MySQL). It keeps everything in memory.
The db_text database system architecture contains
a database is represented by a directory in the local file system. NOTE: when you use db_text in OpenSIPS, the database URL for modules must be the path to the directory where the table-files are located, prefixed by “text://”,
e.g., “text:///var/dbtext/opensips”.
a table is represented by a text file inside database directory.
Internal format of a db_text table
column definition name(type,attr) where types can be int , double , str and attributes be auto , null ,
* each other line is a row with data. The line ends with “\n”.
* the fields are separated by “:”.
* no value between two ‘:’ (or between ‘:’ and start/end of a row) means “null” value.
* next characters must be escaped in strings: “\n”, “\r”, “\t”, “:”.
* 0 — the zero value must be escaped too.
This database interface don’t support the data insertion with default values. All such values specified in the database
template are ignored.
db_mode (integer) – Set caching mode (0 – default) or non-caching mode (1). In caching mode, data is loaded at startup. In non-caching mode, the module check every time a table is requested whether the correspondingfile on disk has changed, and if yes, will re-load table from file.
modparam("db_text", "db_mode", 1)
Exported MI Functions
dbt_dump – Write back to hard drive modified tables.
opensipsctl fifo dbt_dump
dbt_reload – Causes db_text module to reload cached tables from disk. Parameters:
1 db_name (optional) – database name to reload.
2 table_name (optional, but cannot be present without the
db_name parameter) – specific table to reload.
setting module-specific parameters and making initial sanity checks — messages with max_forwards==0, or excessively long requests
-- mi_fifo params --
modparam("mi_fifo", "fifo_name", "/tmp/opensips_fifo")
-- usrloc params --
modparam("usrloc", "db_mode", 2)
modparam("usrloc|auth_db", "db_url", "text:///tmp/opensipsdb")
modparam("auth_db", "calculate_ha1", 1)
modparam("auth_db", "password_column", "password")
modparam("auth_db", "user_column", "username")
modparam("auth_db", "domain_column", "domain")
route{
if (!mf_process_maxfwd_header("10")) {
sl_send_reply("483","Too Many Hops");
exit;
};
if ($ml >= 65535 ) {
sl_send_reply("513", "Message too big");
exit;
};
if (!$rm=="REGISTER") record_route();
//if the request is for other domain use UsrLoc
if (is_myself("$rd")) {
if ($rm=="REGISTER") {
# digest authentication
if (!www_authorize("", "subscriber")) {
www_challenge("", "0");
exit;
};
save("location");
exit;
};
lookup("aliases");
if (!is_myself("$rd")) {
append_hf("P-hint: outbound alias\r\n");
route(1);
exit;
};
# native SIP destinations are handled using our USRLOC DB
if (!lookup("location")) {
sl_send_reply("404", "Not Found");
exit;
};
};
append_hf("P-hint: usrloc applied\r\n");
route(1);
}
route[1]
{
if (!t_relay()) {
sl_reply_error();
};
}
After the starting of a transaction such as REGISTER or INVITE we ensure that subsequent messages withing a dialog should take the path determined by record-routing using “record_route” function.
We used Brekeke SIP server to run our SIP applications . Although there are newer versions of Brekeke SIP server out now . More awesome than before , we prefer using the old one for the sake of not messing with legacy SIP applications . The official site for brekeke is – http://www.brekeke.com/sip/ .
A general architecture of Brekeke SIP server is .
Here are the steps of installing and configuring a Brekeke SIP server .
Step 5 : Once the license is activates , we can goto the console screen after loggin with default username and password sa .
Step 6 : Once we are at console , we could add/ delete / modify parameters like port , start/shutdown status etc . Step 7 : Once the server is all setup , just add the IP and port of SIP server to SIP clients server filed . Now all the SIP request and response will be catered by this SIP Server
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. Kamailio Architecture , Core and Modules
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. Read about Kamailio Transaction management which describes branches , serial and paralle forking and TM module .
Also NAT traversal support for SIP and RTP traffic ( suited to be WebRTC server ) . Read more about kamailio DNS subsystem management , load balancing , NAT and NAThelper modules in Kamailio DNS and NAT
Read more on Kamailio as a WebRTC SIP Server which describes kamailio with mdules websocket , TLS , NATHelper and JSSIP integration
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
Details on Kamailio Security here. Describes todos for snaity , ACL permission , firewall , flood detection , topology hiding and digests
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.
(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). More details on Kamailio as Inbound/Outbound proxy or Session Border Controller (SBC) here
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
Read RTP engine on kamailio SIP server which focuses on setting up sipwise rtpegine to proxy rtp traffic from kamailio app server. Also daemon and kernal modules. ,transcoding , in-kernel packet forwarding , ngcontrol protocol etc.
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
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=1.1.1.1
## 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# 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 msiloalias_db uri_db speeddial avpops auth_db pdt dialog dispatcherdialplan"
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
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 123mysql: [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
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.
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)
----- 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)
Note: leaving NAT pings turned off here as nathelper is <em>only</em> being used for WebSocket connections. NAT pings are not needed as WebSockets have their own keep-alives.
Routing Logic
Main SIP request routing logic processing of any incoming SIP request starts with this route . Read more on Kamailio Call routing and Control
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;
}
}
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
tbd
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 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;
}
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 .
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
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
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
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 the resiliency of data. WORM compliant NAS for storing voice archives over a retention period.
Racks, power supplies, battery backups, cages etc.
Networking DMZs ( Demilitarized Zones) which are interfacing areas between internal servers in the 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 the 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)
Integral Components of a VOIP SIP based architecture
Call Controller
Media Manager
Recording
Softclients
logs and PCAP archives
CDR generators
Session Borer Controllers ( SBCs)
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:
SIP platform components
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 .
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.
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).
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 .
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 , Freswitch
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. Bridges, 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.
RTP ( Real Time Transport Protocol )
RTP handles realtime multimedia transport between end to end network components . RFC 3550 .
Packet structure of RTP
RTP Header contain timestamp , name of media source , codec type and sequence number .
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.
TTS ( Text to Speech )
Alexa Text-to-Speech (TTS) + Amazon Polly
Ivona – multiple language text to speech converter with ssml scripts such as below
<speak><p><s><prosody rate="slow">IVONA</prosody> means highest quality speech
synthesis in various languages.</s><s>It offers both male and female radio quality voices <break/> at a
sampling rate of 22 kHz <break/> which makes the IVONA voices a
perfect tool for professional use or individual needs.</s></p></speak>
check ivona status
service ivona-tts-http status
tail -f /var/log/tts.log
Collecting and Processing PCAPS
VoIP monitor – network packet sniffer with commercial frontend for SIP RTP RTCP SKINNY(SCCP) MGCP WebRTC VoIP protocols
it uses a passive network sniffer (like tcpdump or wireshark) to analyse packets in realtime and transforms all SIP calls with associated RTP streams into database CDR record which is sent over the TCP to MySQL server (remote or local). If enabled saving SIP / RTP packets the sniffer stores each VoIP call into separate files in native pcap format (to local storage).
voip monitor
sngrep
tcpdump
custom made pcap capture and uploader
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 the 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
From SIP packet get the NAPTR record to get the protocl to be used
Inspect SRV record to fetch port to use
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
Call Rate and Accounting
Generally data streams proecssing are used for crtical and voluminious service usage like for – metering/billing – server activity, – website clicks, – geo-location of devices, people, and physical goods
Call Rates are very crticial for billing and charging the calls . Any updates from the customer or carriers or individuals need to propagate automatically and quickly to avoid discrpencies and neagtive margins. CDRs need to be processed sequentially and incrementally on a record-by-record basis or over sliding time windows, and used for a wide variety of analytics including correlations, aggregations, filtering, and sampling.
To acheieve this the follow setup is ideal to use the new input rate sheet values via web UI console or POST API and propagate it quickly to main DB via AWS SQS which is a queing service and AWS lamda which is a serverless trigger based system . This ensures that any new input rates are updates in realtime and maintin fallback values in s3 bucket too
CDR Processing and Billing
CDR store call detail records along with proof of call with tiemstamps , orignation , destination , duaration , rate etc. At the end of month or any other term , the aggregated CDR are cumulatively processed to generate the bill for a user . This heavy data stream needs to be accurately processed and this can be achiveed by using datapipelines like AWS kinesis or Kafka eventstore .
The prime requirnment for the system is to handle enormous amount of call records data in relatime , cater to a number of producers and consumers .
For security the data is obfuscated into blob using base 64 encoding
AWS kinesis – Kinesis Data Streams is sued for for rapid and continuous data intake and aggregation. The type of data used can include IT infrastructure log data, application logs, social media, market data feeds, and web clickstream data
Pros of data streams
This system can handle high volume of data in realtime and produce call uuid specfic reults which can be consumed by consumers waiting for the processed results
Cons of data streams
If not consumed with a pre-specified time duration the processed results expire and are irretrivable . Self implement publisher to store teh processed reults from kisesis stream to data stores like Redis / RDBMS or other storge locations like s3 , dynamo DB. If pieline crashes during operation , data is lost
Data stream should have low latency igesting contnous data from producer and presenting data to consumer .
It should support data sharding ie number of call records grouped and uses a partition Key ( string MD5 hash) to determine which shard the record goes to.
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
