3GPP TS 24.228 -- IMS Signalling flows for Session Initiation
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| Session Initiation: Non Hiding |
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| Session Initiation: Hiding |
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CS Network originated Session routed towards IM CN subsystem, through MGCF
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Single Network Operator performing Origination and Termination
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Mobile Termination, located in home network
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The MGCF in the IM subsystem is a SIP endpoint that initiates requests on behalf of the CS Networks origination
and Media Gateway. The subsequent nodes consider the signalling as if it came from a S-CSCF. The MGCF
incorporates the network security functionality of the S-CSCF. This MGCF does not invoke Service Control, as
this may be carried out in the CS Networks or at the terminating S-CSCF.
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The CS Network establishes a bearer path to the MGW, and signals to the MGCF with a IAM message,
giving the trunk identity, destination information and optionally the continuity indication.
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The MGCF initiates a H.248 command, to seize the trunk and an IP port.
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Request-URI:
Contains the international E.164 number from the user, as obtained from CS Networks
signalling.
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Via:
Contains the IP address or FQDN of the originating MGCF.
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P-Asserted-Identity:
The MGCF inserts the TEL URL containing the subscriber number, as received from
the CS network.
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P-Charging-Vector:
The MGCF inserts this header and populates the icid parameters with a globally unique
value.
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Contact:
SIP URI that contains the IP address or FQDN of the MGCF.
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SDP:
Contains a preconfigured set of codecs supported by the MGW.
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The I-CSCF does not add itself to the Record-Route header, as it has no need to remain in the
signalling path once the session is established.
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Via:
The P-CSCF adds the port number negotiated during the security agreement and the
comp=sigcomp parameter to its Via header.
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Record-Route:
The P-CSCF adds the port number negotiated during the security agreement and the
comp=sigcomp parameter to its own URI.
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P-Media-Authorization:
A P-CSCF generated authorization token. This particular example shows a Policy-Element
generated by "pdf1.home1.net" with credentials "31S14621".
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P-Access-Network-Info:
the UE provides the access-type and access-info, related to the serving access network.
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To:
a tag is added to the To header.
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Contact:
contains a SIP URI with the IP address or FQDN of the UE; it includes the
comp=sigcomp parameter.
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SDP:
the SDP contains the set of codecs supported by UE; it requests a confirmation of the
QoS preconditions for establishing the session.
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Record-Route:
the P-CSCF rewrites the Record-Route header field value to remove the port number
used for the security association and the comp=sigcomp parameter from its own URI.
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P-Asserted-Identity:
P-CSCF inserts the default SIP URI of the user in the P-Asserted-Identity header field.
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P-Charging-Vector:
The S-CSCF adds the identifier of its own network to the terminating Inter Operator
Identifier (IOI) parameter of this header and puts back the originating IOI parameter.
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P-Charging-Function-Addresses:
The S-CSCF passes this header to the I-CSCF for charging.
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