In the WebRTC and IMS post we briefly described the IMS and WebRTC integration. We explained that the WebRTC allows a rapid development of clients. The clients still need some infrastructure for the signalling and services – that’s the IMS. The network element which is acting as an interface between these two worlds – the world of web and the world of IMS is called a WebRTC GW. The WebRTC GW is a collection of network functions which we need for the translation of protocols, interworking and authentication procedures. It can be implemented as an enhancement of already present elements (e.g. eP-CSCF) or we can have a new stand-alone entity.
It is a part of nearly each IMS deployment. Session Border Controller. As the name indicates it sits on a border. A border between two networks. SBC is a controller so it controls all the traffic (both signalling and media) going through. So far so good. But what is really the SBC? What standards we can find? Where is some detail description of the SBC internal architecture? Sure, there are plenty of specs which are somehow describing the role of SBC. The basic one describing SBC is the RFC 5853.
SBC in VoLTE
The meaning of SBC has changed over the last 15 years significantly. We can say that SBCs are solving the problems which are not addressed by other IMS elements – problems with multiple access networks (e.g. IPv4 and IPv6, SIP normalization, VPNs..), security issues (DOS attacks, topology hiding, ..), legislative issues (emergency calls, legal intercept, interworking,..), media related problems (QoS, transcoding, media security,..). And of course, the number of these problems and issues which need to be solved is increasing. So what is the SBC now? As an SBC we understand a network element which is implementing following functionalities: