Software Defined Networks ( SDN) and Network Function Virtulaization ( NFV) for Communication networks

Innovations in telecommunication today are largely driven by the advancements in Open source tech tools, standards and stacks. IP-based video and voice communication systems, Unified Communication systems such as Enterprise CPaaS platforms or even an external independent VoIP provider. The challenge for service providers today is that operating costs are growing faster than revenues. A large number of growing systems and vendors make operation a complex and expensive process.

Discrepancies between traffic growth and revenue growth (Source: Accenture)

Maintaining a network for communication service providers can be a complex and challenging task for several reasons:

  1. Network maintenance and upgrades: Service providers must constantly maintain and upgrade their networks to ensure that they are able to provide reliable service to their customers. This can involve replacing outdated equipment, installing new technology, and troubleshooting issues that arise.
  2. Managing traffic: Service providers must manage the traffic on their networks to ensure that it is distributed efficiently and that users are able to access the services they need. This can be a challenge, especially when the network is congested or there are unexpected spikes in traffic.
  3. Ensuring security: Communication networks are vulnerable to a variety of security threats, including hacking, malware, and denial of service attacks. Service providers must take measures to protect their networks and their customers’ data from these threats.
  4. Managing costs: Maintaining a communication network can be expensive, and service providers must find ways to manage costs while still providing high-quality service to their customers.
  5. Meeting regulatory requirements: Service providers must comply with a variety of regulations, including those related to privacy, data protection, and network security. Failing to comply with these regulations can have serious consequences, including fines and reputational damage.

Network Virtualisation

Network virtualization is the process of creating a virtual version of a network, including the hardware, network topology, and protocols, using software. This allows multiple virtual networks to be created and run on the same physical infrastructure, which can be used to isolate different network environments, test new network configurations, or provide network resources as a service.


  • NFV is SW-defined network functions with separation of HW and SW. Once network elements are SW-based, network HW can be managed as a pool of resources
  • SDN is Interconnecting Virtual Network Functions with separation of control and data plane. Orchestration together with SW domain

There are several ways to implement network virtualization, including using software-defined networking (SDN) technologies, which allow the network to be controlled and managed using software, and using virtualization technologies such as virtual LANs (VLANs) or virtual private networks (VPNs) to create isolated network segments within a larger network. In a virtualized network the setup network functionalities are SW-based over COTS HW. Multiple roles can be made over same HW.

Network Virtualisation for Telcos

Network Virtualisation is an opportunity to build mouldable networks and redefine the architecture to make the infrastructure uniform.Virtual network services lowered CAPEX. Lessening dependencies on proprietary hardware and dedicated appliances.

  • (+) Improves management of risk in a changing and ambiguous environment
  • (+) capacity alteration Network flexibility
  • (+) scalability
  • (+) Service provisioning speed
  • (+) holistic management:
  • (+) granular security

There are several approaches to network virtualization that service providers can use, including:

  1. Network Function Virtualization (NFV): NFV involves virtualizing network functions, such as routers, firewalls, and load balancers, and running them on standard servers or other off-the-shelf hardware using virtualization platforms like VMware or OpenStack.
  2. Software-Defined Networking (SDN): SDN involves separating the control plane (which determines how data is routed through the network) from the data plane (which carries the actual data). This allows the control plane to be more flexible and responsive to changes in the network.
  3. Virtual Private Network (VPN): A VPN allows service providers to create virtual private networks (VPNs) over the public Internet, allowing them to securely connect users to the resources they need.

Service providers can use network virtualization to reduce costs, increase flexibility, and improve the scalability and reliability of their networks. Managed Service Providers (MSPs) can use a single viewpoint and toolset to manage virtual networking, computing and storage resources. However, implementing network virtualization can also be complex and require significant investments in hardware, software, and training.

Software Defined Network (SDN)

A software-defined network (SDN) is a networking architecture that uses software provisioning interfaces to control and manage the flow of traffic in a network. In an SDN, the control plane, which determines how data is routed through the network, is separated from the data plane, which carries the actual data traffic.

The main benefit of an SDN is that it allows the control of the network to be abstracted from the underlying hardware. This makes it possible to use software to dynamically configure the network, rather than relying on fixed configurations that are set using hardware switches and routers. SDN allows network administrators to easily and quickly change the way that data is routed through the network, which can be useful in a variety of scenarios. For example, an SDN can be used to optimize the flow of traffic in a data center, or to quickly reconfigure a network in response to changing traffic patterns or security threats such as DDoS.

SDN planes

Image Credits : Shqip: Arkitektura SDN, 27 June 2021, From Wikimedia Commons, the free media repository Source
  1. Control plane: The control plane is the part of the SDN that determines how data is routed through the network. It consists of a central controller, which is a software application that runs on a server, and a series of software agents that run on the network devices (such as switches and routers). The controller communicates with the agents using a protocol such as OpenFlow, which allows it to control the flow of traffic in the network.
  2. Data plane: The data plane is the part of the SDN that carries the actual data traffic. It consists of the network devices (such as switches and routers) that forward data packets through the network.
  3. Management plane: The management plane is the part of the SDN that is responsible for configuring and managing the network. It consists of a set of tools and applications that allow network administrators to monitor and control the network.
  4. Application plane: The application plane is the part of the SDN that consists of the applications that run on the network. These applications may include things like web servers, email servers, and database servers.

Software-defined network functions separates hardware and software. Once network elements are Software-based, network harware can be managed as a pool of resources. Separating route/switching intelligence from packet forwarding reduces hardware prices as routers and switches must compete on price-performance features.

SDN interconnects Virtual Network Function and orchestrated with SW domain. Enables separation of control and data plane.Setting up networks in an SDN can be as easy as creating VM instances, and the way SDNs can be set up is a far better complement to VMs than plain old physical networks. SDNs enable “network experimentation without impact”. Overcome SNMP limitations and experiment with new network configurations without being hamstrung by their consequences.

  • Infrastructure Savings
  • Reducing margin of Error : By eliminating manual intervention, SDNs enable resellers to reduce configuration and deployment errors that can impact the network.
  • Operational Savings: SDNs lower operating expenses. Network services can be packaged for application owners, freeing up the networking team.
  • Flexibility: SDNs create flexibility in how the network can be used and operated. Resellers can write their own network services using standard development tools.
  • Better Management gives Better visibility into the network, computing, and storage

SDN protocols : OpenFlow, NETCONF. Its applications could be

  • Bandwidth on Demand or test networks.
  • Platform Virtualization for emulation/simulation of Network Nodes (BSS/MSS)
  • SDN based Application Layer Traffic Optimization
  • Intrusion Detection System that can interact with controller in terms of capturing packets, analyzing them for anomaly and sharing results real-time / near real-time with controller.
  • Software-Defined Branch and SD-WAN
  • IP Multi-Media Subsystem (IMS)
  • Session Border Control (SBC)
  • Video Servers
  • Voice Servers
  • Universal Customer Premises Equipment (uCPE)
  • Content Delivery Networks (CDN)
  • Network Monitoring
  • Network Slicing
  • Service Delivery
  • Network security functions such as firewalls, IDS, IPS, vRR, NAT 

Network functions virtualization (NFV)

NFV provides the basic networking functions and SDN assumes higher-level management responsibility to orchestrate overall network operations.

Network Function Virtualization (NFV) is a technology that allows network functions, such as routers, firewalls, and load balancers, to be implemented in software rather than hardware. This allows these functions to be run on standard servers or other off-the-shelf hardware, rather than dedicated appliances.

In an NFV system, network functions are implemented as software called Virtual Network Functions (VNFs). These VNFs are run on virtualization platforms, such as VMware or OpenStack, which allow multiple VNFs to be run on the same physical hardware. To use NFV, a service provider will first define the network functions that it needs in its network, and then create VNFs for each of these functions. These VNFs can then be deployed on virtualization platforms and used to build the service provider’s network.

One of the main benefits of NFV is that it allows service providers to be more flexible and agile in building and managing their networks. Because VNFs can be easily added, removed, or scaled up or down as needed, service providers can quickly respond to changes in demand or new business opportunities. NFV decouples network functions from proprietary hardware appliances (routers, firewalls, VPN terminators, SD-WAN, etc.) and delivers equivalent network functionality without the need for specialized hardware. And this way it helps service providers reduce costs, as they can use standard hardware rather than specialized appliances ( vendor lockins) to implement their network functions.

IMS Virtual Network Functions (VNFs)

IMS. Image Credits Unknown

A traditional appliance based IMS setup is dedicated to every single service, limited hardware/people/process leveraging.Some drawbacks of this approach is

  • Not suited for Heterogeneous Networks that are evolving – inflexible
  • Higher footprint cost per customer/service – high OPEX
  • New services would need a new dedicated network thus high maintenance cost for solios of operation

Virtualisation will help to redesign the network architecture. In an IMS (IP Multimedia Subsystem) system, VNFs might be used to implement a variety of functions, including:

  1. Call Session Control Function (CSCF): The CSCF is responsible for managing call sessions and routing signaling messages between the IMS network and other networks.
  2. Media Gateway Control Function (MGCF): The MGCF is responsible for translating between different media formats, such as voice and video, and for controlling media gateways that connect the IMS network to other networks.
  3. Home Subscriber Server (HSS): The HSS is a database that stores information about IMS subscribers, including their profiles and service subscriptions.
  4. Serving Gateway (S-GW): The S-GW is responsible for routing data packets between the IMS network and the user’s device.
  5. Policy and Charging Rules Function (PCRF): The PCRF is responsible for enforcing policy decisions and charging rules for IMS services.
  6. IP-SM-GW (SMS Gateway): The IP-SM-GW is responsible for routing SMS messages between the IMS network and other networks.
  7. Presence Server: The presence server is responsible for managing presence information (such as availability status) for IMS subscribers.
Multi-tenant subscriber and service environment. Keeping traffic local but with common services & management

Local Data Centre can rapidly build Network Intelligence rationalisation using Real Time Network Analytics on virtul STB, EPC, NAT, BRAS, PE, DHCP , PCRF etc. Core can be simplified and centralised with common and standard interfaces within core network and services to interact with OSS and BSS (standardized billing and fulfillment process).


OpenStack is an open-source virtualization platform. It enables service providers to deploy virtual network functions (VNFs) using commercial off-the-shelf (COTS) server hardware.  OpenStack is widely used in the telecommunications industry, as it allows service providers to build and manage large-scale cloud computing environments that can be used to deliver a wide range of services, including virtualized infrastructure, NFV, and containerized applications. Applying Openstack to virtualize networks :

  1. Infrastructure as a Service (IaaS): OpenStack can be used to create and manage virtualized infrastructure, including compute, storage, and networking resources. This allows service providers to offer users the ability to spin up and manage virtual machines, storage volumes, and other resources on demand.
  2. Network Function Virtualization (NFV): OpenStack can be used as a platform for virtualizing network functions, such as routers, firewalls, and load balancers, and running them on standard servers or other off-the-shelf hardware.
  3. Container orchestration: OpenStack can be used to manage containerized applications, allowing service providers to deploy and scale applications more quickly and efficiently.
Image Credits OpenStack Wiki
Example of  OpenStack implementation. Image source: OpenStack Wiki


More to read :

5G and IMS

In the course of evolution of RAN ( Radio Access layer) technologies, 5G outsmarts 4G-2010 which comes in succession after 3G-2000, 2.5G, 2G -1990 and 1G/PSTN -1980 respectively. Among the most striking features of 5G are :-

  • IP based protocols
  • ability to connect 100x more devices ( IOT favourable )
  • speed upto 10 Gbit/s
  • high peak bit rate
  • high data volume per unit area
  • virtually 0 latency hence high response time

5G + IMS can accommodate the rapid growth of rich multimedia applications like OTT streaming of HD content, gaming, Augmented reality so on while enabling devices connected to the Internet of Things to onboard the telecommunication backbone with high system spectral efficiency and ubiquitous connectivity.


Infact 5G has seen maximum investment in year 2020 in revamping infrastrcuture as compared to other technologies such as IoT or even Cloud. This could be partly due to high rise in high speed communication for streaming and remote communication owining to steep rise in remote learning adn working from home scenarious.

img source statista – global-telecom-industry-priority-investment-areas


5G is specified to operate over range 1 GHz to 100 GHz.

  • Low-band spectrum (below 2.5 GHz) – excellent coverage,
  • mid- band spectrum (2.5–10 GHz) – a combination of good coverage and very high bitrates,
  • high band-spectrum (10–100 GHz) – the bandwidths needed for the highest bitrates (up to 20 Gb/s) and lowest latencies

Workplan for 5G standardisation and release

The Workplan started in 2014 and is ongoing as of now (2018). UPdate

image source : 3GPP “Getting ready for 5G”

3GPP is the standard defining body for telecom and has specified almost all RAN technologies like GSM , GPRS , W-CDMA , UMTS , EDGE , HSPAand LTE before .

5G Core Network

5G Core Network like LTE

5G + IMS

SDN + NFV for 5G deployment

SDN separates the virtualized network infrastructure from its logical architecture. which automates configuration for routing, security etc. 

It also helps in the management of infrastructure for scaling and availability.

Software-defined Networking (SDN) and Network Functions Virtualization (NFV) are advancing the deployment of 5G systems. The separation of user and control plane are essentially making the system very modular thereby increasing the application to various traffic types 

  • IMS signalling
  • Smart city sensors, cameras 
  • Web services 
  • Self-driving cars 
  • Real-Time Communications / VoIP
  • Augment Reality(AR) , Virtual Reality ( VR)
  • Real Time Gaming
  • Mission Critical Data / Push to Talk ( MCPTT)
  • buffered streaming ( non conversational Video)

Dynamic Network Slicing

Network Slicing allows mobile operators to partition a single network into multiple virtual networks. This allow network operator to use one physical network to cater to many kinds of service networks with varrying usecases around bandwidth, network latency, processing, resiliency, business requirnments.

Dynamic Network Slicing allows the network resources like radio networks, wire access, core, transport and edge networks to be divided into multiple logical networks to meet requirnments of diverse use cases. [2]

Horizontal Slicing (Infrastructure Sharing)Vertical Slicing (QoS Slicing)
The virtual infristructure is shared between different tenants for control and operations ( think IaaS)creating service instances

Service Based Architecture (SBA)

Virtualization and slicing allow us to create Service Based Architectures ( SBA). This allows control plane and user plane sepration( CUPS). It also allows sepration between access and core network.

The modular function design allows concurrent access to services as well as decoupling of stateless processors and statefull backend ( database).

  • (+) network capability exposure
  • (+) scalability
  • (+) redundancy

Applications of 5G

5G targets three main use case

  • enhanced mobile broadband (eMBB),
  • massive machine type communications (mMTC)
  • ultra-reliable low latency communications (URLLC) (also called critical machine type communications (cMTC))
sources : whitepaper ericsson


Wifi 6

Wi‑Fi is a trademark of the Wi-Fi Alliance. It belongs to the family of radio technologies commonly used for wireless local area networking (WLAN) devices.

Current and older Wifi standards

Standards operate on varying frequencies, deliver different bandwidths, and support different numbers of channels.


Transmits at 5 GHz frequency band of the radio spectrum with 54 megabits of data per second.

Orthogonal frequency-division multiplexing (OFDM) splits radio signals into several sub-signals before they reach a receiver to reduce interference.


Transmits at 2.4 GHz with a speed of 11 megabits of data per second

Complementary code keying (CCK) modulation to improve speeds


Transmits at 2.4 GHz but faster up to 54 megabits of data per second. It uses OFDM coding.


Speeds 140 megabits per seconds. Backward compatible with a, b and g. 

Transmit up to 4 streams of data, each at a maximum of 150 megabits per second, but most routers only allow for 2 or 3 streams.

Backward compatible with 802.11n and thus others. 450 megabits per second on a single stream. It is also called 5G WiFi because of its frequency band .

(+) Very High Throughput (VHT)

Wifi 6

Wi-Fi CERTIFIED 6 networks enable lower battery consumption in devices, making it a solid choice for any environment, including smart home and Internet of Things (IoT) uses.

Wifi Components

  • wireless access point (AP) allows wireless devices to connect to the wireless network.
    takes the bandwidth coming from a router and stretches it so that many devices can go on the network from farther distances away. Gives useful data about the devices on the network, provide proactive security, and serve many other practical purposes.
  • Wireless routers are hardware devices that Internet service providers use to connect you to their cable or xDSL Internet network.
    combines the networking functions of a wireless access point and a router.
  • Mobile hotspot – feature on smartphones with both tethered and untethered connections
    share your wireless network connection with other devices

Wifi performance

Wi-Fi operational range depends on factors such as the frequency band, radio power output, receiver sensitivity, antenna gain and antenna type as well as the modulation techniquea and propagation charestristics of the signal

Transmitter power
Compared to cell phones and similar technology, Wi-Fi transmitters are low power devices. In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as FCC Part 15 in the US. Equivalent isotropically radiated power (EIRP) in the European Union is limited to 20 dBm (100 mW).

An access point compliant with either 802.11b or 802.11g, using the stock omnidirectional antenna might have a range of 100 m.

Wifi Security

WEP (Wired Equivalent Privacy) 

The client connects to a WEP-protected network, the WEP key is added to some data to create an “initialization vector” IV

WiFi Protected Access version 2 (WPA2) 

Successor to WEP and WPA. It uses either TKIP or Advanced Encryption Standard (AES) encryption.

WiFi Protected Setup (WPS) 

WPS ties a hard-coded PIN to the router for setup is vulnerable for exploitation by hackers


WPA3 uses the latest security methods, higher grader security protocols

Disallow outdated legacy protocols

Require use of Protected Management Frames (PMF)

  • (+) Increased protection from password guessing attempts
  • Better password protection through Simultaneous Authentication of Equals (SAE), which replaces Pre-shared Key (PSK) in WPA2-Personal.


192-bit minimum-strength security protocols and cryptographic tools

Authenticated encryption: 256-bit Galois/Counter Mode Protocol (GCMP-256)

Key derivation and confirmation: 384-bit Hashed Message Authentication Mode (HMAC) with Secure Hash Algorithm (HMAC-SHA384)

Key establishment and authentication: Elliptic Curve Diffie-Hellman (ECDH) exchange and Elliptic Curve Digital Signature Algorithm (ECDSA) using a 384-bit elliptic curve

Robust management frame protection: 256-bit Broadcast/Multicast Integrity Protocol Galois Message Authentication Code (BIP-GMAC-256)

References :
[2] Wikipedia

5G and IMS

striking features of 5G – entirely IP based ability to connect 100x more devices ( IOT favourable ) speed upto 10 Gbit/s high peak bit rate high data volume per unit area virtually 0 latency hence high response time

4G/Long Term Evolution (LTE), VOLTE

LTE stands for Long Term Evolution and is a registered trademark owned by ETSI (European Telecommunications Standards Institute) for the wireless data communications technology and a development of the GSM/UMTS standards.

4G/Long Term Evolution (LTE), VOLTE

4G/ Long Term Evolution (LTE)

LTE stands for Long Term Evolution and is a registered trademark owned by ETSI (European Telecommunications Standards Institute) for the wireless data communications technology and a development of the GSM/UMTS standards.

  • Both radio and core network evolution
  • All-IP packet-switched architecture
  • Standardised by 3GPP
  • (+) Lower CAPEX ans OPEX involved

LTE evolved from an earlier 3GPP system known as the Universal Mobile Telecommunication System (UMTS), which in turn evolved from the Global System for Mobile Communications (GSM). Also it is aligned with 4G (fourth-generation mobile)

It is backward compatible with GSM/EDGE/UMTS/CDMA/WCDMA systems on existing 2G and 3G spectrum, even hand-over and roaming to existing mobile networks.

Motivation for evolution – Wireless/cellular technology standards are constantly evolving for better efficiency and performance.LTE evolved as a result of rapid increase of mobile data usage. Applications such as voice over IP (VOIP), streaming multimedia, videoconferencing , cellular modemetc.

It provides packet-switched traffic with seamless mobility and higher qos than predecessors. Also high data rate, throughput, low latency and packet optimized radioaccess technology on flexible bandwidth deployments.

Timeline of Evolution 

  • GSM  : calls  on circuit switching ( CS ) between 2 parties for communication. Dedicated circuits are used for voice and SMS.
  • GPRS : packet switching (PS) is introduced for data services
  • UMTS / 3G : network elements begin evolving into PS . No changes to core.
  • EPC / LTE/VOLTE : No circuit switched domain at all .

LTE Performance

Peak Data Rate

  • uplink – 75Mbps(20MHz bandwidth)
  • downlink – 150 Mbps(UE Category 4, 2×2 MIMO, 20MHz bandwidth), 300 Mbps(UE category 5, 4×4 MIMO, 20MHz bandwidth)

Carrier bandwidth : Range from 1.4 MHz up to 20 MHz. Ultimately bandwidth used by carrier depends on frequency band and the amount of spectrum available with a network operator.

Mobility 350 km/h

Coverage 5 – 100km with slight degradation after 30km

LTE architecture supports hard QoS and guaranteed bit rate (GBR) for radio bearers.

Technology used in LTE

All interfaces between network nodes are IP based in LTE.
Duplexing – Time Division Duplex (TDD) , Frequency Division Duplex (FDD) and half duplex FD

MIMO ( Multiple Input Multiple Output ) transmissions Allows the base station to transmit several data streams over the same carrier simultaneously.

Multiple Access Schemes

  • uplink: SC-FDMA (Single Carrier Frequency Division Multiple Access) 50Mbps+ (20MHz spectrum)
  • downlink: OFDM (Orthogonal Frequency Division Multiple Access) 100Mbps+ (20MHz spectrum)
  • Multi-Antenna Technology, Multi-user collaborative MIMO for Uplink and TxAA, spatial multiplexing, CDD, max 4×4 array for downlink

Modulation Schemes : QPSK, 16QAM, 64QAM(optional)

4G/ LTE Architecture

Primarily composed of 3 parts UE, E-UTRANand EPC.

1. User Equipment (UE)

  • Mobile Termination (MT)
  • Terminal Equipment (TE) 
  • Universal Integrated Circuit Card (UICC) : also known as the SIM card for LTE equipments. It runs an application known as the Universal Subscriber Identity Module (USIM).

2. Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)

handles the radio communications between the mobile and the evolved packet core. High level representation for  eNodeB or eNB

Role of eNB : sends and receives radio transmissions to all the mobiles using the analogue and digital signal processing functions of the LTE air interface. eNB also controls the low-level operation of all its mobiles, by sending them signalling messages such as handover commands.

3. Evolved Packet Core (EPC)

This sub system resembles IMS environment.

SGW (Serving Gateway) for routing and forwarding of user data packets

Packet Data Network (PDN) Gateway (P-GW) communicates with the outside world simillar to GGSN ( GPRS support node ) and SGSN ( serving GPRS support node ) in UMTS and GSM.

Home Subscriber Server (HSS) is a central database that contains information about all the network operator’s subscribers. Almost simillar to HLR/AAA in 2G /3G architcture.

Mobility management entity (MME) controls the high-level operation.

LTE Roaming Service

For a roming user in Visited-PLMN, the user is connected with the E-UTRAN, MME and S-GW of the visited LTE network. However, LTE/SAE allows the P-GW of either the visited or the home network to be used, as shown in below:

For roaming prepaid charging, accounting flows are made to access prepaid customer data, via P-Gateways or CSCF in an IMS environment.

VoLTE ( Voice over LTE)

A-SBC (Access Session Border Controller) consists of P-CSCF and ALG/AGW. This connects access network (LTE) to IMS core.

  • Connect IP networks, including IPv4 and IPv6 interworking, NAT traversal, etc.
  • Security
    • DDos prevention
    • Topology hiding
    • Encryption
    • P-CSCF maintains the security associations between itself and the UE
  • QoS control
  • trancoding
  • media service handling using Application layer gateway (ALG) access gateway (AGW)

Core IMS has

  • I-CSCF (Interrogating Call Session Control Function) which provides Location service to find the correct S-CSCF for each subscriber
    •  for peer networks the I-CSCF is the first point of contact.
  • S-CSCF (Serving Call Session Control Function) SIP session management and routing
    • connect to HSS for policies
    • invokes Application Servers (TAS, IPSMGW)

Telephony Application Server (TAS) is the application layer of the telecommunication system which adds intelligience and business logic to the platform. We can design call flows and usecases such as

  • address normalization
  • call diverting/ forwarding/ forking
  • Smart screening/ barring( whitelisting , greylisting , blacklisting)
  • It connects to MRF – Media Resource Function
    • media mixer or as a media server for tones, announcements

To proivide compatibility with 2G , 3G and prior systems ths archietcture has

IPSMGW enable support for SMS over SIP 

MGCF – Media Gateway Control Function to support Circuit switched network

BGCF – Breakout Gateway Control Function to find routing based on ENUM/DNS (e.g. PSTN number)

Interop between 3G and LTE user endpoints

Interoperation between IMS networks

Interoperation between multiple IMS networks and LTE operators

Interconnect Session Border Controller (I-SBC) handles the boundary where service providers interconnect and exchange inbound outbound SIP sessions. It consists of

  • Interconnect Border Control Function (IBCF)
    • Inter-Working Function (IWF)
  • Transition Gateway (TrGW)

Voice over Wifi and WebRTC with LTE

Voice over Wifi and WebRTC with LTE

TWAG or ePDG gateway is used to integrate the Wireless LAN access network into the Mobile Network Packet Core – EPC Network.

TWAG (Trusted Wireless Access Gateway) in the Wi-Fi core provides trusted access to the UE( User Equipment). The TWAG is then connected directly to the P-GW (Packet Gateway) in the Evolved Packet Core (EPC).


Advanced features planned for LTE include

  • LTE devices capable of CAT6 speeds (Category 6 )
  • Increased peak data rate – downlink 3 Gbps, Uplink 1.5 Gbps ( 1 Gbps = 1000 Mbps)
  • Spectral efficiency from 16bps/Hz in R8 to 30 bps/Hz in R10
  • Carrier Aggregation (CA)
  • Enhanced use of multi-antenna techniques
  • Support for Relay Nodes (RN)


Also read about previous generations of telecom namely 2 G and 3G

5G and IMS

MIMO ( multiple-input and multiple-output )

SISO – Single Input Single Output
SIMO – Single Input Multiple output
MISO – Multiple Input Single Output
MIMO – Multiple Input multiple Output

Multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation.
Key technology for achieving a vast increase of wireless communication capacity over a finite electromagnetic spectrum.

Antenna configuration – implies antenna spatial diversity by useing arrays of multiple antennas on one or both ends of a wireless communication link
boost channel capacity.
combats multipath fading
enhance signal to noise ratio,
create multiple communication paths

Applies to wifi
IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi)
as well as cellular networks
HSPA+ (3G)
WiMAX (4G)
Long Term Evolution (4G LTE)
power-line communication for 3-wire installations as part of ITU standard and HomePlug AV2 specification

Large capacity increases over given bandwidth and S/N resources
Greater throughputs on bands below 6 GHz,

multi-user MU-MIMO

simultaneous independent data links to multiple users over a common time-frequency resource

massive MIMO

enable the expansion of the useful spectrum to microwave and millimeter wave bands within the framework of 5G cellular communication.

microdiversity MIMO

MIMO modes (60m)

Diversity – Alamouti algorithm
Beam forming – create and aim the antenna pattern electronically
Spatial multiplex – use of precoding and shaping to unravel the multipath signals

challenges faced by mobile equipment vendors implementing MIMO in small portable devices.


3main categories: precoding, spatial multiplexing (SM), and diversity coding.


multi-stream beamforming ( signal is emitted from each of the transmit antennas with appropriate phase and gain weighting such that the signal power is maximized at the receiver input ) , increases reception and reduce multipath fading

In line-of-sight propagation, beamforming results in a well-defined directional pattern. However, conventional beams are not a good analogy in cellular networks, which are mainly characterized by multipath propagation. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas, and precoding with multiple streams is often beneficial. Note that precoding requires knowledge of channel state information (CSI) at the transmitter and the receiver.

Spatial multiplexing

High-rate signal is split into multiple lower-rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels.

increasing channel capacity at higher signal-to-noise ratios (SNR).

Diversity coding

when there is no channel knowledge at the transmitter , a single stream is transmitted. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity.

Ref :

Evolution of voice Communication

From ARPANET(Advanced Reseracha nd Prjects Agency Network) in 1973 by US dept of defence , invention of HTTP in 19196 and finally evoluation of SIP in 2000 and availiability of broadband ethernet services, the telecom landscape has evolved. As far as infrastructure, services, and contents are concerned, the VoIP industry is witnessing a migration from POTS / PSTN/  Legacy integrations to  NGN (Next Generation  Network).

NGN was implemented globally as a means to change the cost base, agility and service capabilities of telecoms providers. The evolved architecture for the transition is one that provides flexibility to service providers by enabling them to deploy new services on IP based technologies, while leveraging existing services and infrastructure as long as it makes sense. This post describes the evolution of voice communication in access , transport and  session layers respectively.

Year of dev1970-19841980-19991990-20022002-20102010-2015
Launch year1987 by Telstra Australia 1991 in Finland by Elisa1998 pre-commercial launched by NTT DoCoMo in Japan , branded as FOMA.2009 in Stockholm (Ericsson and Nokia Siemens Networks systems) 2019, in South Korea,
Frequency30 Khz1.8 Ghz1.6 – 2 Ghz2- 8 Ghz3 – 30 Ghz
bandwidth2.4 Kbps14.4 – 50 Kbps ( GPRS)
64 Kbps – 1 Mbps ( EDGE)
144 Kbps – 2 Mbps100 Mbps – 1 Gbps> 1Gbps
upto 35.46 Gbps
Core LayerPSTNPSTNpacketinternetinternet
Compiled by @altanai

Access Layer

We see that the speed enhances considerably with every generation- 1G offerd 2.4 kbps, 2G offered 64 Kbps based on GSM, 3G offered 144 kbps – 2 mbps whereas 4G offers 100 Mbps – 1 Gbps with LTE technology.

It is to be noted that  one of requirements set by IMT-2000 was that speed should be at least 200Kbps to call it as 3G service and 384kbps ( wth stationary speeds of 2Mbps) for a “true” 3G.

ip transformation in access layer
IP transformation in access layer

Note that voice calls in GSM, UMTS and CDMA2000 were circuit switched but with newer technology voice calls became packet switched too and a lot of rereginerring was required.

LTE (Long Term Evolution) is a series of upgrades to existing UMTS technology involving OFDM and MIMO and newer upgrade were called LTE advanced also. Upcoming 5G offers speeds upto 35.46 Gbps.

Transport Layer

ip transformation in transport layer
IP transformation in transport layer

Session Layer

While 2G introduced services like SMS , MMS , internal roaming , conference calls, call hold and billing based on services e.g. charges based on long distance calls and real time billing which were unheard of in 1G , there were challenges in terms of page load speed for interactive websites .

As 3G came into picture, usecases also enhanced with multimedia features siuch as fast web browsing, maps navigation, email, video downloading, picture sharing and other Smartphone technology

ip transformation in session layer
ip transformation in session layer

Read more about IMS ( IP multimedia System ) IP Multimedia Subsystem ( IMS )

IMS at work from visiting to home location
Access network agnostic

It is noteworthy that SKYPE provided VoIP services ( since 2003) much before mobile phone had 2G/3G ( 2010). In current times with many fantastic options to choose from( whatapp , FB messenger , insta cht , Viber , Hangouts ..) given the high bandwidth with 4G/5G and mych advanced media / signal processing tech , the glocal voip scene is touching 400 mililion subscribers and looks very attractive with 1.5$ billion market.

Bodies and projects behind the evolutions


The GSM Association (GSMA) of mobile operators and related companies are devoted to supporting the standardising, deployment and promotion of the GSM mobile telephone system. The GSM Association was formed in 1995. It organises GSMA Mobile World Congress, in addition to smaller, targeted events GSMA Mobile Asia Expo and the GSMA NFC & Mobile Money Summit. Spanning more than 220 countries, the GSMA unites nearly 800 of the world’s mobile operators, as well as more than 200 companies in the broader mobile ecosystem, including handset makers, software companies, equipment providers, Internet companies, and media and entertainment organisations.


The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations, known as the Organizational Partners. The initial scope of 3GPP was to make a globally applicable third-generation (3G) mobile phone system specification based on evolved Global System for Mobile Communications (GSM) specifications within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU). The scope was later enlarged to include the development and maintenance of the Global System for Mobile Communications (GSM) including GSM evolved radio access technologies (e.g. General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE)) an evolved third Generation and beyond Mobile System based on the evolved 3GPP core networks, and the radio access technologies supported by the Partners (i.e., UTRA both FDD and TDD modes). It is an evolved IP Multimedia Subsystem (IMS) developed in an access independent manner

3GPP standardization encompasses Radio, Core Network and Service architecture. The project was established in December 1998 and should not be confused with 3rd Generation Partnership Project 2 (3GPP2), which specifies standards for another 3G technology based on IS-95 (CDMA), commonly known as CDMA2000. The 3GPP support team (also known as the “Mobile Competence Centre”) is located at the European Telecommunications Standards Institute (ETSI) headquarters in Sophia-Antipolis (France).


The Open Mobile Alliance (OMA) is a standards body which develops open standards for
the mobile phone industry. Network-agnostic : The OMA only standardizes applicative protocols; meant to work with any cellular network technologies being used to provide networking and data transport. These networking technology are specified by outside parties. In particular, OMA specifications for a given function are the same with either GSM, UMTS or CDMA2000 networks.
Legal status :The OMA is a British limited company.

Standard specifications The OMA maintains a number of specifications, including

  • Browsing specifications, now called “Browser and Content”, previously called WAP browsing. In their current version, these specifications rely essentially on XHTML Mobile Profile.
  • MMS specifications for multimedia messaging
  • OMA DRM specifications for Digital Rights Management
  • OMA Instant Messaging and Presence Service (OMA IMPS) specification, which is a system for instant messaging on mobile phones (formerly known as Wireless Village).
  • OMA SIMPLE IM Instant messaging based on SIP-SIMPLE
  • OMA CAB Converged Address Book, a social address book service standard.
  • OMA CPM Converged IP Messaging
  • OMA Client Provisioning (OMA CP) specification for Client Provisioning.
  • OMA Data Synchronization (OMA DS) specification for Data Synchronization using SyncML.
  • OMA Device Management (OMA DM) specification for Device Management using SyncML.
  • OMA BCAST specification for Mobile Broadcast Services.
  • OME RME specification for Rich Media Environment.
  • OMA PoC specification for Push to talk Over Cellular (called “PoC”).
  • OMA Presence SIMPLE specification for Presence based on SIP-SIMPLE.
  • OMA Service Environment
  • FUMO Firmware update
  • SUPL, an IP-based service for assisted GPS on handsets
  • MLP, an IP-based protocol for obtaining the position/location of mobile handset
  • WAP1, Wireless Application Protocol 1, 5-layer stack of protocols


The IP Multimedia Subsystem (IMS) Profile for Voice and SMS, documented in this Permanent Reference Document (PRD), defines a profile that identifies a minimum mandatory set of features which are defined in 3GPP specifications that a wireless device (the User Equipment (UE)) and network are required to implement in order to guarantee an interoperable, high quality IMS-based telephony service over Long Term Evolution (LTE) radio access. The scope includes the following aspects:

· IMS basic capabilities and supplementary services for telephony.
· Real-time media negotiation, transport, and codecs.
· LTE radio and evolved packet core capabilities.
· Functionality that is relevant across the protocol stack and subsystems.

IR 94 Profile for Video Services

This document defines a voice over IMS profile by listing a number of Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Evolved Packet Core, IMS core, and UE features which are considered
essential to launch interoperable IMS based voice. The defined profile is compliant with 3GPP specifications.

Enterprise communication systems

On premise private branch exchanges ( PBX ) were the first kind of business telephone systems to which the analog PSTN systems of the company were conneced. These analog circuits were then replaced by digital PBX which provided enhanced features liek screening , voicemails , shared lines.

In the current landscape , the digital PBX of the company is connected to the external telco privider via a SBC or SIP trunking service .

An ompremise LAN based voIP system can be accessed from outside via a VPN on SSL/ IPsec. Although it incures greater CAPEX but ensufe maximum control and ownership of the data . Many time the local laws mandate the server to be hosted with a partuclat geographical area too where an on premise setup and data centre is used.

Enterprise communication shifts from on-premise to SaaS (cloud)

As for remote worksforce and employees working from home (such as during lockdown , pandemics ) it is even more crticial for enterprises to maange inter communication between teams and keep the communication private ie not using piblic messaging platforms , hence the role of cloud based PBX integrated with secure and end to end encrypted telco providers is of prime importance .

To read how a SME can setup their own flexible and scable enterprise comunication system read –

VoIP/ OTT / Telecom Solution startup’s strategy for Building a scalable flexible SIP platform

With the advent of other disruptive technologies such as free and opensource codecs in browser with WebRTC and well defined framework and standards, voIP definetly looks detsined to expand by leaps and bounds.


2G to 3G – generation of telecom

Second generation or 2G of telecom emerged a decade after (1990) its predecessor 1G (1980). Although the history of telecom evolution truely beings with internet and further engineered with PSTN, analog voice and switches we shall omit them discussing here as they are truly legacy now.  You can read more about Legacy telecom here-

Legacy Telecom Networks

I use the term legacy telecom system many a times , but have not really described what a legacy system actually is . In my conferences too I am asked to just exactly define a…

We have seen the evolution of teelcom access networks through generations happening pretty quickly recently. While earlier it was a decade that led to the jump between generations, the recent jumps from 3G to 4G to 5G happening fairly quickly.  In this article let us dive into what enhancements went into 2G and its successor 3G, since

Where 2G is referred to as the GSM era , 2.5 G as the GPRS with GSM era. The following two diagram denote the service operators architecture nodes in both these times .

2G / GSM era

As compared to its predecessor 1G which used FDMA ( Frequency Division Multiplexing ) for channelization , 2G used used TDMA and CDMA for dividing the channels .

Note that in pure 2G there was only circuit switched communication services .


2.5G or GPRS era

The advent of 2.5 G, in later part of 1990s, bought packet switching for data access along with existing circuit switching for voice network. While 1G and pure2G relied solely on circuit switching, now 2.5 G used both circuit switched and packet switching. The speed provided by General Packet Radio Service ( GPRS ) was ~= 50 Kbps.

Digital voice was introduced with multiple access technologies like CDMS ( Core Division Multiple access )


2.75G ( EDGE)

EDGE( Enhanced Data Rates for GSM evolution) was deploying on GSM technologies and was also standardised by 3GPP technologies . EDGE delivers higher bit-rates per radio channel, resulting in a threefold increase in capacity and performance compared with an ordinary GSM/GPRS connection with speed upto 1 Mbps.

In terms of transmission techniques, EDGE and its varients used Gaussian minimum-shift keying (GMSK), EDGE uses higher-order PSK/8 phase shift keying (8PSK) for the upper five of its nine modulation and coding schemes.

Note that the processes such as billing etc had begun merging for both the circuit switched and packet switched networks .


Even though 2G evolution was enough to sustain voice abd video calls, the mobile industry became “smarter” and data hungry for faster services ( mobile gaming , video conferencing ,video streaming, social media interactions are some of the usecases ). It became necessary to bring in faster speed while evolving towards and hence was born 3G in early 20000. Some of the tecehnolgies which were branded 3G are

 UMTS (Universal Mobile Telecommunications System) 

Core technology for 3G ,


3.5G ( HSPA)

Now 3G was further succeeded by 3.5G ( HSPA – High Speed Downlink Packet Access ) with max theoritical 21.6 Mbps.

Eventually 4G ( LTE Long Term Evolution ) overtook the indutry with newer technologies but the impressive array of technologies in transaition between 2G to 3G to 4G was awe inspirinig indeed .

References :

Also Read

4G/Long Term Evolution (LTE), VOLTE

LTE stands for Long Term Evolution and is a registered trademark owned by ETSI (European Telecommunications Standards Institute) for the wireless data communications technology and a development of the GSM/UMTS standards.

5G and IMS

striking features of 5G – entirely IP based ability to connect 100x more devices ( IOT favourable ) speed upto 10 Gbit/s high peak bit rate high data volume per unit area virtually 0 latency hence high response time

L1, L2 ,L3 equipment and L3 vs L4 switches

Layer 1: Physical Layer

Layer 1 Data : Physical bits

Layer 1 Equipment : Physical mediums copper ethernet cables, fiber optic, ethernet hubs
or even wireless mediums such as WiFi Bluettoth , Microwave , IR( Infra Red )Remote or other over the air technologies.

Factors affecting physical layer protocols could be
Wiring standards such as T568A and B for Ethernet
Radio frequencies such as Wi-Fi, BLE, Zigbee , LORA

Layer 2 links or transmistts data between nodes in a network, it involves protocol like FrameRelay.

The sublayers of this layer are

  • 2A. MAC ( Medium Access control) : prevent collision in half duplex network. Although half duplex is non existant now, duplex negotations have simmilar collision avoidance.
  • 2B. LLC ( Logical Link Control) : mechanisms for multiplexing Layer 3 Protocol such as it can acts as interface between the media access control sublayer and the network layer.

Layer 2 Data : The data packets are usally referred to as Frames and are structured to have a header containing source and destination adress as well as payload.
VLAN(Virtual LAN) implemeted atop this layer protcols helps to split up broadcast domains by allowing to sedment devices to their own dedicated LAN.

Layer 2 Equipment : More intelligent than Layer 1 – Switches , Bridges , Network Card.
While a hub ( Layer 1 ) would simply broadcast traffic to all ports, a Switch could read the destnation MAC address and only forward to the specific port that MAC address is linked to.

Layer 3 : Network Layer

This layer defines a logical address of an endpoint.
Unlike MAc address ( from Layer 2 ) which is fixed for a device and assigned onetime by the vendor during the manufacturing process, Layer 3 endpoints are not fixed and could be a static IP configuration or a DHCP automated configuration

Layer 3 Data : Organization of Data at this layer is referred to as a packet, which is a stateless grouping of data

Layer 3 Equipment : Firewalls can operate on this layer( can operate on upper layers too) using stateless static filtering.

While some protocol are layer specifc other can operate in multiple layers such as MultiLayer Switch which make decision based on following :
– MAC address and Protocol field in L2 data link frame
– IP address and Protocol field in L3 network layer header
– Port numbers in L4 transport layer header

L2 Switch

Hardware-based switches, which use the MAC address of the host’s network interface cards (NICs) to decide where to forward frames.
Mostly carried out without frame modification unless the frame needs to be encapsulated for a different medium such as wired to wireless.

  • (+) Efficient since they have least modificatons to frame
  • (-) acting as multipot brdges causes performance issues. Increasing size of network and slow convergence of spanning tree is probelmatic for such using broadcast/multicast.

L3 Switches

Determine paths based on logical addressing.
These also check and recompute layer-3 header checksums and examine and update the time to live (TTL) field for validity.
Network switches can perform almost all of the functions of a router however they are designed for the specific physical medium.

  • (+) lower network latency as a packet can be routed without making extra network hops to a router.

Layer 4-6 switch

Used by web switch, content switch, Softswitch. These are build on applications on higher layer in network stack and are more domain orietned such as

  • Load balancer for Web traffic
  • NAT (Network Address Traversal)
  • SBC ( Session Border Controller )

Layer 7 switch

Recognize application level transactions and may use URL to distribute load, also using a cache such as
CDN ( Content Delivery Network).

Switches operating on higher layers, also referred to by some vendors as AppSwitches, can route packets based on application information can provide superior quality of service (QoS) for IP voice and media streams.
It can help with domain-specific load-balancing capabilities for voice-over-IP gateway and IP PBX ( eg packet-tagging techniques, SIP handlers to prioritize, Differentiated Services ).