LTE seems to be the technology of choice to many mobile operators around the world. Since the beginning of (wireless) time, there has always been one technology which is touted as the best performing technology , its typical characteristics being high speed, low latency and low cost per bit. The flavor of this generation (4G) is LTE. VoIP support in LTE has been the hot button issue in the recent times and has grabbed a lot of media attention. This article examines the perceived need for LTE VoIP and the proposed solutions. Need for LTE VoIP I see that the follwing points are often made to support need for VoIP over LTE. 1) LTE without operator supported VoIP is just a dumb pipe. Companies like Skype will benefit if LTE-VoIP is not supported. 2) VoIP is a revenue-generating application that is mandatory for profitability. 3) VoIP is needed for future killer apps such as IMS VCC, voice+video etc. There are five different (proposed) solutions that I know of today for VoIP over LTE. Each solution has its advantages and disadvantages. Companies promoting each of these solutions have big personal interests in doing so.
CSFB – Old wine in old bottle
Circuit Switched Fall Back (CSFB) LTE handsets revert, or “fall back,” to an existing 2G or 3G radio network whenever a subscriber needs to place or receive a voice call. This means that the handset should be capable of at least two technologies – a) LTE and b) GSM, UMTS or CDMA.
VoLGA , MSC server etc – New wine in old bottle
VoLGA uses Packet-switched (PS) access and Circuit-switched (CS) core and tunnels the circuit-switched traffic over the LTE IP-based network. Handsets do not fall back to a 2G or 3G but voice is packetized and delivered natively over LTE. Handful of 3GPP members broke away and formulated this “standard”.
Nokia voice server is a MSC server that supports VoIP. The Fast Track update to the Nokia VoIP Server makes it possible for mobile operators to use their existing circuit-switch core networks to manage voice traffic over LTE networks. The servers can also be used if operators choose to deploy IMS architecture.
Mavenir Systems Inc. and Acme Packet have announced a new approach which is similar to Nokia's approach. The idea is to couple Mavenir's MSC platform and Acme's session border controllers (SBCs), creating a technology combo that allows mobile operators to deliver VoIP using their legacy infrastructures.
IMS voice – New wine in new bottle
IP Multimedia Subsystem (IMS) is the only 3rd Generation Partnership Project (3GPP) -endorsed approach for delivering voice and messaging services over LTE. Single Radio Voice Call Continuity (SR-VCC) address coverage gaps in LTE networks.
SR-VCC - new wine & old wine
When VoIP is supported in LTE, there will be a need for handing over calls from LTE to CS domain. This handover procedure is known as SR-VCC. In SR-VCC, the UE performs a coordinated radio level handover in combination with a change from IMS VoIP to CS voice using IMS procedures of service continuity.
