VoLTE Part 2

In this post, I intend to cover VoLTE architecture.

VoLTE Architecture
There are three components that need to be understood before understanding the VoLTE architecture , Evolved packet core,Access network and control portion of the network. Its in line with the architecture concept of single box radio thats getting popular from LTE. This flat architecture, reduces the latencies and improves the signalling speeds.

Evolved Packet Core : EPC contains a total of three entities. One in control place (MME) and two Gate ways in user plane. (S-GW/P-GW). MME , mobile management entity has controls the user authentication authorization functions.Other MME functions include NAS signalling , security , tracking area lists , CSFB and SRVCC inter technology handovers. S-GW assists the UE in inter/intra enodeB handovers , packet forwarding , routing etc, P-GW on the other hand manages gateways towards PDN. It is also in charge of policy and charging enforcements.

Access Network : Its the User Equipment and the eNodeB.

Control Network : The control network has three major componets. IMS (IP multimedia system) , PCRF (Policy and charging rule function) , HSS (Home subscriber server). As the names are self explanatory lets not get into too many details. In short IMS is responsible for IP connectivity , roaming , QoS , IP policy and service control. PCRF creates CDRs using the programmed call charging functions. Last but not least HSS maintains subscriber and service related data.

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VoLTE Part 1

We had discussed the need and challenges for voice over LTE .. Now lets understand it by digging deeper..

Although all the operators will be moving to 3GPP eventually. The underlying 3G technologies are different. Some operators have CDMA, some have GSM and hence it is going to be a difficult but necessary transition. Theoretically most of the solutions look very very attractive.. Its when the real situations come, the challenges are visible. There are two angles to the whole LTE deployment strategy. CDMA angle and GSM/WCDMA angle.


GSM/WCDMA :

Initially the operators will have to support circuit switched fall back. In the later stages, when LTE coverage is obtained throughout the region, Single radio voice call continuity needs to be achieved to reach the end result of all IP networks !


CDMA : 

I always feel that GSM is a very very complex system and difficult to understand. :(
These operators need to support Simultaneous Voice and LTE (SV-LTE) or Simultaneous Voice and Data (SV-DO) or evolved high rate packet data (eHRPD) and achieve the end goal of all IP networks controlled by IMS.

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