IMS Signalling flows for session initiation: Non Hiding
MO#1a / S-S#1a / MT#1a (page 2 of 3)
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Mobile origination, roaming
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Different network operators performing origination and termination
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Mobile termination, roaming
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UE1 determines which media flows should be used for this session, and which codecs should be used
for each of those media flows. If there was any change in media flows, or if there was more than one
choice of codec for a media flow, then UE1 includes a new SDP offer in the PRACK message sent to
UE2.
For this example, assume UE1 chooses H.263 as the codec to use for the single video stream.
Therefore, UE1 sends a new SDP offer in the PRACK request.
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Request-URI:
takes the value of the Contact header of the received 183 Session Progress response.
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Via:
takes the value of either the IP address or FQDN of the originating UE.
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Cseq:
takes a higher value than that in the previous request.
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Security-Verify:
contains the security agreement as represented by the received Security-Server header.
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After determining the final media streams, UE1 initiates the reservation procedures for the
resources needed for this session.
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P-CSCF1 removes the Security-Verify header and associated "sec-agree" option-tags prior to
forwarding the request. As the Proxy-Require header is empty, it removes this header completely.
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Via:
P-CSCF1 adds the port number negotiated during the security agreement and the
comp=sigcomp parameter to its own entry in the Via header.
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UE2 initiates the reservation procedures for the resources needed for this session.
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When the resource reservation is completed, UE1 sends the UPDATE request to the terminating
endpoint, via the signalling path established by the INVITE request.
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Request-URI:
Takes the value of the Contact header of the received 183 Session Progress response.
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Via:
Takes the value of either the IP address or FQDN of the originating UE.
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Cseq:
Takes a higher value than that in the previous request.
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Security-Verify:
Contains the security agreement as represented by the received Security-Server header.
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P-CSCF1 removes the Security-Verify header and associated "sec-agree" option-tags prior to
forwarding the request. As the Require and Proxy-Require headers are empty, it removes these headers
completely.
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P-Charging-Vector:
P-CSCF1 adds the GPRS access network information to this header.
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P-Charging-Vector:
S-CSCF1 removes the GPRS access network information to this header and stores it.
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Via:
P-CSCF2 adds the port number negotiated during the security agreement and the
comp=sigcomp parameter to its own entry in the Via header.
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