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, located in home network
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UE1 is located in the home network, and determines the P-CSCF via the CSCF discovery procedure.
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P-CSCF1 knows the name/address of the S-CSCF from a prior Registration performed by UE1.
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UE1 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.
UE1 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 P-CSCF1 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:
UE1 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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P-CSCF1 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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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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P-Asserted-Identity:
P-CSCF1 inserts the TEL URI in the P-Asserted-Identity header field and it also removes the
P-Preferred-Identity header field.
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P-Charging-Vector:
P-CSCF1 inserts this header and populates the icid parameters with a globally unique value.
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S-CSCF#1 validates the service profile of this subscriber and evaluates the initial filter criterias. For
this example, assume no Application Server involvement.
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As S-CSCF1 knows that the next hop I-CSCF is in the same home network (and therefore, a loose
router), it includes a Route header.
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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:
S-CSCF1 adds the identifier of its own
network to the originating Inter Operator
Identifier (IOI) parameter of this header.
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I-CSCF2 sends a query to the HSS to find out the S-CSCF of the called user. The HSS responds with
the address of the current S-CSCF for the terminating subscriber.
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I-CSCF2 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) UE2 Contact address and
the next hop CSCF for UE2.
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Route:
Built from the Path header stored at registration.
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Via:/Record-Route:
S-CSCF2 adds itself.
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P-Called-Party-ID:
Includes the dialled URL with its parameters.
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Via:
P-CSCF2 adds the port number negotiated during the security agreement and the
comp=sigcomp parameter to its Via header.
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Record-Route:
P-CSCF2 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:
UE2 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:
Contains the set of codecs supported by UE2. It requests a confirmation of the
QoS preconditions for establishing the session.
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P-CSCF2 authorizes the resources necessary for this session. The approval of QoS commitment either
happens at this stage or after 200 OK of INVITE based on operator local policy.
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Record-Route:
P-CSCF2 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-CSCF2 inserts the default SIP URI of the user in the P-Asserted-Identity header field.
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P-Charging-Vector:
S-CSCF2 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:
S-CSCF2 passes this header to I-CSCF2 for charging.
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P-CSCF1 authorizes the resources necessary for this session. The approval of QoS commitment either
happens at this stage or after 200 OK of INVITE based on operator local policy.
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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 "9BV3072". "00" at the end
of the authorization token is required to pad to a multiple of 4 bytes.
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Record-Route:
P-CSCF1 rewrites the Record-Route header to add the port number negotiated
during the security agreement and the comp=sigcomp parameter to its own SIP URI.
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