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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Mobile Origination, located in home network
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Single Network Operator performing Origination and Termination
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Mobile termination, roaming, without I-CSCF in home network
providing configuration independence,
terminating UE is busy, and not
able or not willing to answer the call
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The UE is located in the home network, and determines the P-CSCF via the CSCF discovery procedure.
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The P-CSCF knows the name/address of the S-CSCF from a prior Registration performed by the UE.
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UE#1 builds an SDP offer containing bandwidth requirements and characteristics for
each set of codecs that it is capable of supporting for this session. It assigns local port numbers for
each possible media flow.
UE#1 is willing to establish a multimedia session comprising a
video stream and an audio stream. The video stream supports two codecs, either H.263 or MPEG-4
Visual. The audio stream supports the AMR codec.
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Request-URI:
contains the international E.164 number from the user.
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Via: contains the IPv6 address or FQDN (fully qualified domain name)
of the originating UE.
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Route: contains the P-CSCF address learnt during P-CSCF discovery,
plus the elements from the
Service-Route header from registration. The P-CSCF URI contains the port number learnt
during the security agreement negotiation.
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P-Preferred-Identity: the user provides a hint about the identity
to be used for this session.
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P-Access-Network-Info: the UE provides the access-type and access-info,
related to the serving access.
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Privacy: the user does not require privacy,
therefore the Privacy header is set to the value "none" as
specified in RFC 3325 and RFC 3323.
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Security-Verify: Contains the security agreement
as represented by the received Security-Server header.
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The P-CSCF adds itself to the Record-Route header and Via header. As the request is forwarded to an
interface that is not compressed, the own P-CSCF SIP URI does not contain the "comp=sigcomp"
parameter.
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The P-CSCF 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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P-Asserted-Identity: P-CSCF inserts the TEL URI in
the P-Asserted-Identity header field and it also removes
P-Preferred-Identity header field.
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P-Charging-Vector: The P-CSCF inserts this header and
populates the icid parameters with a globally unique value.
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Request-URI:
In the case where the Request-URI of the incoming INVITE request to S-CSCF contains a
TEL-URL, it has to be translated to a globally routable SIP-URL before applying it as
Request-URI of the outgoing INVITE request. For this address translation the S-CSCF uses
the services of an ENUM-DNS protocol according to RFC 2916, or any other suitable
translation database.
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P-Charging-Vector: The S-CSCF adds the identifier of its own
network to the originating Inter Operator
Identifier (IOI) parameter of this header.
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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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S-CSCF#2 remembers (from the registration procedure) the UE Contact address and
the next hop CSCF for this UE.
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Route:
Built from the Path header stored at registration.
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Via:/Record-Route:
S-CSCF adds itself.
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P-Called-Party-ID:
Includes the dialled URL with its parameters.
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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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