VoLTE (2)

Warsaw University of Technology

Karthik KrishneGowda KrishneGowd a

VoLTE Voice Over LTE, LTE, IMS & the Future Future of Rich Media Services in the 4G Era

pg. 1


Karthik KrishneGowda

Introduction:

The GSMA announced

VoLTE (Voice over LTE) initiative was formally on 15th February 2010. In establishing the VoLTE

initiative, GSMA has adopted the work of the One Voice Initiative as the basis of the work to lead the global mobile industry towards a standard way of delivering voice and messaging services for Long-Term Evolution (LTE). Using IP Multimedia Subsystem specifications developed by 3GPP as its basis, GSMA have expanded upon the original scope of One Voice work to address the entire end-to-end voice and SMS ecosystem by also focusing on Roaming and Interconnect interfaces, addition the interface between customer and network.

in

The One Voice Profile:

One Voice profile defines a minimum mandatory set of features a wireless device (the UE) and network are required to implement in order to guarantee an interoperable, high quality IMS-based telephony service over LTE radio access. The scope includes the following aspects •

IMS

basic

capabilities

and

supplementary

services

for

telephony • Real-time media negotiation, transport, and codec’s. • LTE radio and evolved packet core capabilities • Functionality that is relevant across the protocol stack and

subsystems

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The UE and network protocol stacks forming the scope of the One Voice profile are depicted in the figure below:

Migration from 3G to LTE Mobile service providers have not adopted much SIP or IMS today. However, nothing precludes them from doing so, and initiatives like Rich Communication Suite may incent adoption of SIP / IMS ahead prior to LTE deployment. The area with the largest SIP adoption is the core and IP interconnect borders, which does lay nice groundwork for migration to the 3G and 4G access networks. LTE is on the 5-year horizon for some 3G service providers, so they have time to roll-out IMS ahead of their 4G deployment. VoLGA and VoLTE both offer migration, but only VoLTE offers services beyond voice and messaging of yesteryear. MSC VoIP is an interim step as well, where some investment is preserved for both voice-the MSCs at the outset-and the multimedia-SIP infrastructure for the years ahead.

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Evolution of VoLTE:

The above diagram clearly indicates the evolution of the VoLTE. Voice Over LTE, IMS & the Future of Rich-Media Services in the 4G Era explores how the mobile industry's two most lucrative applications – voice and SMS – can be offered across LTE networks, and how IMS can be used to introduce new, interoperable rich-media communications services, such as videoand presence-based communication, messaging, collaboration, and conferencing. At the network level, the strategic options available to mobile operators to support real-time communications services over 4G/LTE and converged 2G/3G/LTE networks. This includes interim options such as CS fallback, SIP-enabled mobile switching centers (MSCs), convergence servers, and Voice over LTE Generic Access (VoLGA); as well as the long-term, strategic shift to IMS, which starts with the GSM Association's Voice over LTE (VoLTE)

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initiative and evolves to Multimedia Telephony (MMTel) services based on 3GPP IMS.

GSMA VOLTE Overview: As depicted in the below diagram , in LTE and 3G PS are fully packet switched as compared to 2G/3G uses SR-VCC and IMS centralized services. This concept supports almost all services and different network interface

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Architecture of VoLTE by ZTE:

IMS-based solutions and leveraging its expertise in LTE, ZTE, demonstrated how voice will be incorporated into next generation networks as depicted in figure 2. IMS-based solutions and leveraging its expertise in LTE, ZTE demonstrated how voice will be incorporated into next generation networks. Implementing VoLTE is one of the biggest challenges for operators as they deploy LTE networks. ZTE is cooperating with CSL to research this area and to gain valuable experience in voice applications over the LTE network. This lays the foundation for CSL in terms of future IMS-based LTE and also provides a significant reference for other operators

GSMA

VoLTE

–

Underlying

Key

Principles

the GSM community of around 4 billion connections is built based on a single technology being used across all networks and all phones and Single

implementation

devices.

promotes

scale –

This has led to a diverse range of GSM-enabled devices,

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and massive choice of form principles have driven the

factor for the end-user. Similar movement of HSPA from phones to

dongles, and now to be embedded in laptops and consumer electronics. For a Voice over LTE implementation to continue this model, it must be applicable to the entire LTE industry, and not subject to fragmentation or undue diversity. Single

implementation

reduces

when many ways deployed into networks, with one another in

complexity –

implementing a single service are allow customers to communicate

of to an

interoperable and inter-network fashion is very complex. Interworking functionality is required which can affect the overall quality of service by inserting delay, potentially being a point of failure and not always guaranteeing the compatibility of the two service implementations.

Single implementation enables Roaming – the GSMA has long held a

role in defining the way in which Roaming takes place in the mobile telecommunications world. For Roaming to work, every device must implement the interfaces between itself and the network it is trying to connect to in exactly the same way. Similarly, every network must accept devices that are attaching to it because of the common implementation of interfaces between the two entities. This everyone adheres to a single common standard.

only

happens

when

Issues of VoLTE: There are o many issues and challenges to solve with respect to VoLTE handsets - especially in CDMA networks.

The complexities

include radio issues, the implementation of SIP UAs and SIP compression (SIGCOMP). But just as important are the issues associated between

with

voice

different

LTE. This handset.

call

radio

creates

handover

access

challenges

-

in

particular

technologies, in

both

the

e.g. network

handover CDMA

and

and

the

Another interesting challenge in the handset will be the design of

the

SIP

UA

in

the

handset.

Our

experiences

in

early

IMS

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trials showed that many of the handsets had a separate SIP stack for every application on the handset. This could mean one SIP stack for voice calls and another for messaging applications or RCS (Rich Communications Suite). It would also mean registrations with the network for each application.

multiple This is

probably not the ideal situation from the carrier perspective but presumably things have since the early IMS trials.

evolved

in

the

last

5

or

so

years

Conclusion: It would appear as though momentum is continuing to grow for LTE - but it is still early. LTE deployment will take years to reach a large percentage of subscribers. However, the growth of mobile data is pushing many carriers in developed economies to take a close look at deploying LTE sooner as opposed to later. There will be LTE phones early 2011, but there will be no dual-radio phones with voice from UMTS/CDMA and LTE being the primary data network (with 3G for non-LTE markets for data coverage). For a truly mobile LTE voice and multimedia communications device would come into the market in 2012. Although, once the LTE radio is available on a phone, anyone could make a call using over-the-top clients.

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References:

1. One

Voice:

Voice

over

IMS

profile

by

AT&T,

Orange,

Telefonica, TeliaSonera, Verizon, Vodafone, Alcatel-Lucent, Ericsson, Nokia Siemens Networks, Nokia, Samsung and Sony Ericsson.

2. Mobile telephony evolution - supporting voice over LTE by

Ericsson

3. VoLTE

for

Public Safety Broadband Networks from

Maria

Palamara (Alcatel Lucent) 4. http://www.heavyreading.com/ 5. http://wwwen.zte.com.cn

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VoLTE (2)

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