HSPA Voice over IP
In the previous chapters we described how voice over long term evolution (VoLTE) works and we believe VoLTE is a driver for mobile voice over Internet protocol (VoIP) and a technology where mobile VoIP will take off first. However, we also believe that voice over high speed packet access (VoHSPA) could be used to speed up VoIP deployment by having a nationwide IP network with a combination of two technologies in a fast and cost-effective way (no need to have LTE everywhere to provide unified VoIP experience). When VoIP is deployed in HSPA as well, then a packet (see Section 5) handover can be used from LTE to HSPA instead of single radio voice call continuity (SR-VCC) to minimise impact to legacy circuit switched (CS) networks. Also VoHSPA boosts the (wideband code division multiple access) WCDMA/HSPA network's voice capacity (see Section 7.2) compared to the current CS voice deployments and it further gives the possibility to start re-farming voice from CS [mainly from global system for mobile communications (GSM)] to IP (LTE/HSPA) and makes it possible for operators to release some GSM frequencies to LTE.
The very same IP multimedia subsystem (IMS) functionality which is required for VoLTE (as described in Chapter 5.6.1) can be used to provide VoHSPA. The efficient deployment of VoHSPA requires the following essential radio and packet core capabilities:
- Support of the Robust header compression (RoHC). Since the IP header itself without compression ...