At this point, additional radio bearers must be set up. The network sends an RRC Connection Reconfiguration to activate the EPS bearer. The UE confirms successful completion with an RRC Connection ReconfigurationComplete message and then finalizes the Attach procedure and accepts the activation of the EPS bearer.It should be noted that the way a default…

Before sending any Session Initiation Protocol (SIP) requests, the UE must perform “P-CSCF Discovery”, the process of identifying (by address) the correct Proxy-Call Session Control Function (P-CSCF). The P-CSCF addressmay be discovered in one of three different ways: It may be stored in the IP Multimedia Services Identity Module (ISIM). The UE may request it…

After Authentication, Security and UE Capability requests, the network accepts the Attach request and activates the EPS bearer context. Once that has happened and the UE has also established a PDP context, a typical IMS SIP client registration (Figure 4) begins: The IMS client attempts to register by sending a REGISTER request to the P-CSCF.…

Suppose the UE now intends to monitor a specific “registration event”. In this context an event may be a callback (to provide audio for a shared web event, for example) or an update to a “buddy list” or a message waitingindicator. In general, this means that the UE is asking to be notified any time…