A Method for Enabling a Calling User Equipment, UE, to Retry a Session Initiation Protocol, SIP, Call Attempt to a Called UE, Over a Circuit Switched Domain

摘要

A method for enabling a calling User Equipment, UE, to retry a Session Initiation Protocol, SIP, call attempt to a called UE, over a Circuit Switched domain, in a telecommunication network, wherein said called UE has a SIP session established towards said telecommunication network, wherein said method comprises the steps of receiving, by a Proxy Call Session Control Function, P-CSCF, node, an indication that a signalling bearer between said called UE and said telecommunication network is released, wherein said signalling bearer is associated with said SIP session, transmitting, by said P-CSCF node, to a Serving Call Session Control Function, S-CSCF, node, triggered by said received indication, a subscribe message for informing said S-CSCF node that said P-CSCF unsubscribes to registration events pertaining to said called UE due to the released signalling bearer such that said S-CSCF node is able to initiate a CS retry when said telecommunication network receives a SIP call attempt from said calling UE to said called UE