IMS is an architecture for real-time multimedia (voice, data, video, and messaging) services using a common IP network. It defines a layered architecture. According to the 3GPP specification, IMS entities are classified into six categories:
Session management and route (CSCF, GGSN, and SGSN)
Database (HSS and SLF)
Interworking elements (BGCF, MGCF, IM-MGW, and SGW)
Service (Application Server, MRFC, and MRFP)
Strategy support entities (PDF)
Billing
Interoperability with the SIP infrastructure requires a session border controller to decrypt the WebRTC control and media flows. A media node is also set up for transcoding between WebRTC codecs and other legacy phones. When a gateway is involved, the WebRTC voice and video peer connections are between the browser and the border controller. In our case, we have been using Kamailio in this role (refer to Chapter 2, Making a Standalone WebRTC Communication Client). Kamailio is an open source SIP server capable of processing...