3gpp 3gpp ts 33203 v12670 2014 0609 90 release 12 the

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3GPP 3GPP TS 33.203 V12.67.0 (2014-0609) 90 Release 12
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The P-CSCF shall then check whether the Security-Client header exists in the received REGISTER message: - If the REGISTER request contains a Security-Client header then, for an initial registration, the P-CSCF shall select the sec-mechanism and mode (cf. Annex H) from the corresponding parameters offered in the Security- Client header according to its priorities. If the P-CSCF selects the sec-mechanism "ipsec-3GPP" and the mode "trans" it shall perform the steps required for IMS AKA without NAT traversal. If the P-CSCF selects the sec-mechanism "ipsec-3GPP" and the mode "UDP-enc-tun" it shall perform the steps required for IMS AKA with NAT traversal. If the P-CSCF selects the sec-mechanism "tls" it shall perform the steps required for SIP Digest with TLS. - If the REGISTER request does not contain a Security-Client header, or the P-CSCF does not select any sec- mechanism from the Security-Client header, then the P-CSCF shall behave as follows: - If the REGISTER request is received over a TLS connection, the P-CSCF shall perform the steps required for Digest with TLS prior to Initial registration according to Clause O.2.3. - Otherwise If the REGISTER request does not contain an Authorization header and was received over an access networks defined in 3GPP specifications then the P-CSCF shall perform the steps required for GIBA. If the REGISTER request was not received over a TISPAN NASS or 3GPP network then the P-CSCF shall perform the steps required for SIP Digest without TLS. If the REGISTER request was received over a TISPAN NASS access, then the P-CSCF shall perform the steps required for NBA as well as the steps required for SIP Digest without TLS, unless it is configured to behave differently or the P-CSCF only supports either SIP Digest without TLS or NBA. If the NBA- related query from the P-CSCF to the TISPAN NASS fails the P-CSCF shall not continue to perform the NBA-related steps. - For a subsequent registration, the P-CSCF shall continue to use the selected mechanism. NOTE 1: Note that Annex N states that SIP Digest authentication shall not apply to access networks defined in 3GPP specifications. NOTE 2: The use of Authorization headers in IMS REGISTER requests is defined in TS 24.229 [8]. NOTE 3: The inclusion of an Authorization header in a REGISTER request is optional for NBA and optional for SIP Digest. Therefore, when a REGISTER request is received over a TISPAN NASS the P-CSCF cannot know whether the request relates to SIP Digest or NBA unless it is configured to select one of the schemes according to certain criteria, e.g. IP address range. The steps required for SIP Digest and for NBA are not in contradiction. Rather, for NBA the P-CSCF needs to perform additional steps, namely an exchange with the TISPAN NASS and an inclusion of NASS location information in the REGISTER request, on top of the steps required for SIP Digest.
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