For secure transport of Diameter messages, see TS 33.210
Accounting functionality (Accounting Session State Machine, related command codes and AVPs) is not used on the Cx interface.
Both between the I-CSCF and the HSS and between the S-CSCF and the HSS, Diameter sessions are implicitly terminated. An implicitly terminated session is one for which the server does not maintain state information. The client does not need to send any re-authorization or session termination requests to the server.
The Diameter base protocol includes the Auth-Session-State AVP as the mechanism for the implementation of implicitly terminated sessions.
The client (server) shall include in its requests (responses) the Auth-Session-State AVP set to the value NO_STATE_MAINTAINED (1), as described in RFC 6733
. As a consequence, the server does not maintain any state information about this session and the client does not need to send any session termination request. Neither the Authorization-Lifetime AVP nor the Session-Timeout AVP shall be present in requests or responses.
Diameter messages over the Cx and the Dx interfaces shall make use of SCTP RFC 4960
This clause specifies the use of the Diameter routing AVPs Destination-Realm and Destination-Host.
If an I-CSCF or S-CSCF knows the address/name of the HSS for a certain user, both the Destination-Realm and Destination-Host AVPs shall be present in the request. Otherwise, only the Destination-Realm AVP shall be present and the command shall be routed to the next Diameter node, e.g. the SLF or a Diameter Proxy Agent (see TS 29.228
), based on the Diameter routing table in the client.
If the next Diameter node is an SLF, then once the SLF has returned the address or the destination HSS (using Redirect-Host AVP), the redirected request to the HSS shall include both Destination-Realm and Destination-Host AVPs. If the next Diameter node is a Diameter Proxy Agent, the Diameter Proxy Agent shall determine the destination HSS. The Diameter Proxy Agent, based on the result of this determination of the destination HSS, shall modify the Destination-Realm AVP and Destination-Host AVP of the request appropriately. The Diameter Proxy Agent shall then append a Route-Record AVP to the request and shall send the request to the destination HSS. Consequently, the Destination-Host AVP is declared as optional in the ABNF for all requests initiated by an I-CSCF or an S-CSCF.
If the response is routed back to a Diameter Proxy Agent, the Diameter Proxy Agent shall send the response back to the I-CSCF or S-CSCF without modifying the Origin-Realm AVP and Origin-Host AVP. The response shall contain the Origin-Realm AVP set to the realm of the HSS together with the Origin-Host AVP set to the HSS that sent the response. The S-CSCF shall store the HSS realm and HSS address for each Public Identity, after the first request sent to the User Identity to HSS resolution function.
Requests initiated by the HSS towards an S-CSCF shall include both Destination-Host and Destination-Realm AVPs. The HSS obtains the Destination-Host AVP to use in requests towards an S-CSCF, from the Origin-Host AVP received in previous requests from the S-CSCF. Consequently, the Destination-Host AVP is declared as mandatory in the ABNF for all requests initiated by the HSS.
Destination-Realm AVP is declared as mandatory in the ABNF for all requests.
The HSS, S-CSCF and I-CSCF shall advertise support of the Diameter Multimedia Application by including the value of the application identifier (see clause 6
) in the Auth-Application-Id AVP within the Vendor-Specific-Application-Id grouped AVP of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands.
The vendor identifier value of 3GPP (10415) and ETSI (13019) shall be included in the Supported-Vendor-Id AVP of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands, and in the Vendor-Id AVP within the Vendor-Specific-Application-Id grouped AVP of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands.