5.12. Third-Generation Release 4 Convergence Over IP/MPLS

The 3G Release 4 standard introduces the concept of a split architecture, as previously discussed. For 3G voice traffic, the connection between the MGWs has a control plane and a user plane. The control plane is IP-based Signaling System 7 (SS7), as defined by SIGTRAN, enabled through the MSC server. The user plane must handle TDM for 2G and ATM or IP for 3G R4.

SIGTRAN is the Internet Engineering Task Force (IETF) working group responsible for producing protocol specifications that provide reliable datagram service and user layer adaptations for SS7 and Integrated Services Digital Network (ISDN) communications protocols. SIGTRAN is an extension of the SS7 protocol supporting the same application and call management standards as SS7 using an IP transport called Stream Control Transmission Protocol (SCTP). In the mobile network, SCTP is used to carry PSTN signaling over IP.