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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Different network operators performing origination and termination,
with configuration hiding by originating network operator
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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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During registration, the home network allocates an S-CSCF in the home network.
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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 the P-CSCF address learnt during P-CSCF discovery, including the port number
negotiated during the security agreement, plus the elements from the Service-Route
header from registration.
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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 network.
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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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Contact:
SIP URI that contains the IP address or FQDN of the originating UE.
It also contains the port number where UE1 wants to receive protected messages.
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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 SIP 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 performs an analysis of the destination address, and determines the network operator to whom the
destination subscriber belongs. Since the originating operator desires to keep their internal configuration
hidden, S-CSCF#1 forwards the INVITE request to I-CSCF#1.
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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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Route:
Topmost Route header set to the I-CSCF that will perform the translation needed to maintain
configuration independence.
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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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Via:/Record-Route:
Translated to maintain configuration independence of the home#1 operator.
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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 UE2. 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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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-Asserted-Identity:
S-CSCF2 inserts the TEL 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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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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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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