The Telecom Protocols

SRVCC enables continuity of voice call anchored in IMS network, when UE changes its access network from packet based in eUTRAN to circuit based GERAN or UTRAN, without requiring the UE to have simultaneous access to both the radio network.   It accomplishes this by enhancing the MMEs, serving E-UTRAN and the 3GPP CS MSC serving GERAN/UTRAN such that when the UE is still anchored within the E-UTRAN network and triggers a measurement report indicating a need for handover (HO) to GERAN/UTRAN, the MSC can initiate IMS service continuity procedure towards the IMS domain in addition to preparing for a handover into its GERAN/UTRAN access, before the UE is directed to change its access network to GERAN/UTRAN.     The SRVCC feature requires the new Sv interface between MSC and MME. Sv Interface runs over UDP. Following messages are exchanged over Sv Interface:   - PS to CS Request - PS to CS Response - PS to CS Complete Notification - PS to CS Complete Acknowledge - PS t

Capability Exchange: When two peers established transport connection, they must exchange the capability exchange message. this message allows the discovery of peer's identity and its capabilities. Once transport layer is established, CER and CEA exchanged to determine the capability of peer endpoint followed by DWR/DWA. In below example DiameterNodeA start diameter connection with DiameterNodeB after transport layer connection established. In case of TCP (Syn/Syn-Ack) and  SCTP (Init/Init-Ack/Coockie Echo) exchanged. In case of SCTP Connection establishment(CER, CEA, DWR, and DWA) are exchanged with setting out-of-order delivery false to avoid race-condition and for connection termination (DPR/DPA) set the timer to receive out-of-order message before terminating the connection.               DiameterNodeA                     DiameterNodeB                                     <------Transport Layer Established--------->                ---------------------- CER -------

    Diameter is AAA (authentication, Authorization, and Accounting protocol) such as RADIUS protocol. As name suggest, DIAMETER is double of RADIUS protocol. while there are many difference between two protocols but one of the main difference is diameter provides the security and reliability because diameter uses TCP/SCTP on transport level, it uses TLS and DTLS. whereas RADIUS runs over the UDP.   Diameter protocol is peer to peer protocol so that any node can initiates a request, all data delivered in form of AVPs and provides following facilities:   - Ability to exchange messages and deliver AVPs. - Capability Negotiation - Error Notification - Application specific services.     Diameter base protocol is run on port 3868 for both TCP and SCTP. TLS and Datagram Transport Layer Security (DTLS) uses port 5658. It is assumed TLS run on top of TCP and DTLS is run on top of SCTP. When no transport connection available with peer node, peer should try to connect it