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  • IMS Procedures Tutorial

    Any discussion of IMS protocols must start with a dialogue describing the procedures being implemented. It is important to note that there is no “one size fits all” procedural flow; IMS in LTE offers a lot of flexibility to both network equipment manufacturers and network operators. Note that the processes described here are strictly from […]

    August 10, 2021
  • 1. IMS Procedure: Public Data Network (PDN) connectivity

    As in legacy 3GPP technologies, the UE starts connection by issuing a Radio Resource Control (RRC) Connection Request. Note that while either the UE or the network can trigger the connection request, it is always initiatedby the UE. This request includes both the UE identity information and the call establishment cause (i.e.Mobile Originating Signaling or […]

    August 10, 2021
  • 2. IMS Procedure: Authentication

    Now that NAS signaling is established, the network initiates an Authentication Request or challenge. Once the UE’s Authentication Response is deemed valid, the network sends a NAS Security Mode Command. Note that while neither the Authentication Request nor the Authentication Response is integrity-protected, the Security Mode Command is protected. The UE then sends a Security […]

    August 10, 2021
  • 3. IMS Procedure: Bearer Setup and EPS Attach

    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 […]

    August 10, 2021
  • 4. IMS Procedure: P-CSCF Discovery

    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 […]

    August 10, 2021
  • 5. IMS Procedure: SIP Registration

    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. […]

    August 10, 2021
  • 6. IMS Procedure: Event Subscription

    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 […]

    August 10, 2021
  • 7. IMS Procedure: VoLTE Call

    The initial stages of setting up a VoLTE call are the processes of the initial attach, P-CSCF discovery and creating the default bearer for SIP signaling (by registering with the IMS network and subscribing to a registration eventpackage).The first step in a VoLTE call setup is a SIP INVITE request initiated by the calling UE. […]

    August 10, 2021
  • The two types of SMS in 5G

    Within 5GC, SMS Function (SMSF) supports SMS over NAS (SMSoNAS) defined in 3GPP TS 23.501. Besides, SMSoIP can also be considered as IMS based SMS solution under 5G network. SMSoIP can be deployed simultaneously with voice service over IMS to provide both voice and short message service. It is recommended to use SMSoNAS solution if […]

    August 10, 2021
  • Voice and Video services over IMS in 5G

    5G voice/video service will still be provided based on IMS (5G as one of the access modes for IMS voice/video), and the introduction of 5G voice/video will not change the IMS network architecture. Support of IMS based services is based on GSMA NG.114 “IMS Profile for Voice, Video & Messaging over 5GS”. In the early […]

    August 10, 2021
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