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Answer: The 2G GSM systems were the first digital systems that performed the authentication of subscriber. The mobile was assigned a temporary identifier after the authentication so that it does not has to send the mobile subscriber’s permanent identity ‘IMSI’ on the air interface. And the voice was encrypted. However, 2G systems suffered from two [...]

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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 [...]

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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 [...]

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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 [...]

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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 [...]

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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 as [...]

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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.The [...]

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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 [...]

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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. [...]

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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 [...]

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