VoLTE Services

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Serviços VoLTE

Transcript of VoLTE Services

  • In this voice call session establishment sequence the originating user presents the SIP INVITE to the originating networks IMS. In this case the P-CSCF will determine the route to the S-CSCF and forward the message. The S-CSCF will route the message to an AS determined by the filter criteria; the AS may modify the INVITE according to the requirements for the session. This may include modifying the session description and providing routing information to the intended network. The S-CSCF will route the INVITE message toward the destination user via the I-CSCF. The I-CSCF will determine which S-CSCF should handle the session request. it may do this by interrogating the HSS. The IMS components will then begin to forward the INVITE toward the user within that network, applying filter criteria if necessary. This initial routing and forwarding of the session request is important, not just to deliver the message to the destination party, but also to establish the actual route the subsequent message will follow. Each of the SIP servers (CSCFs) will add or remove routing labels from the SIP header information to ensure accurate routing. The destination system will indicate that an attempt to contact the user is being made (100 Trying). In this example, when the destination party responds to the initial INVITE, it sends a progress message 183, which starts the media negotiation process in which both ends determine which media codecs should be used for the session. The subsequent messages, PRACK from the originating party and 200 OK from the

  • destination, also form part of this media negotiation.