The IP Multimedia Subsystem (IMS) is built on Internet Engineering Task Force (IETF) protocols like Session Initiation Protocol (SIP) and Session Description Protocol (SDP). In IMS, voice traffic is served using Internet Protocol (IP). IMS aim is to merge mobile and fixed voice communications and any other Internet services. Network congestion causes lack of resources due to excess traffic over a single path between routers which is predominantly caused by speed mismatches and aggregation due to a gigabit Ethernet link feeding a fast Ethernet or traffic travelling over to low speed WAN links from a high speed LAN links in a network.

Papers:

Camarillo, Gonzalo; García-Martín, Miguel A. (2007). The 3G IP multimedia subsystem (IMS) : Merging the Internet and the Cellular Worlds.

H. Schulzrinne and J. Rosenberg, "The Session Initiation Protocol: Providing Advanced Telephony Services Across the Internet," Bell Labs Technical Journal, 1999