Section: 20.7 Use of the Supported-Features AVP on the SGmb reference point
Content: The Supported-Features AVP is used during session establishment to inform the destination host about the required and optional features that the origin host supports. The client shall, in the first request in a Diameter session indicate the set of supported features. The server shall, in the first answer within the Diameter session indicate the set of features that it has in common with the client and that the server shall support within the same Diameter session. Any further command messages shall always be compliant with the list of supported features indicated in the Supported-Features AVPs during session establishment. Features that are not advertised as supported shall not be used to construct the command messages for that Diameter session. Unless otherwise stated, the use of the Supported-Features AVP on the SGmb reference point shall be compliant with the requirements for dynamic discovery of supported features and associated error handling on the Cx reference point as defined in clause 7.2.1 of 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [105]. The base functionality for the SGmb reference point is the 3GPP Rel-11 standard and a feature is an extension to that functionality. If the origin host does not support any features beyond the base functionality, the Supported-Features AVP may be absent from the SGmb commands. As defined in clause 7.1.1 of 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [105], when extending the application by adding new AVPs for a feature, the new AVPs shall have the M bit cleared and the AVP shall not be defined mandatory in the command ABNF. As defined in 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [105], the Supported-Features AVP is of type grouped and contains the Vendor-Id, Feature-List-ID and Feature-List AVPs. On the SGmb reference point, the Supported-Features AVP is used to identify features that have been defined by 3GPP and hence, for features defined in this document, the Vendor-Id AVP shall contain the vendor ID of 3GPP (10415). If there are multiple feature lists defined for the SGmb reference point, the Feature-List-ID AVP shall differentiate those lists from one another. On receiving an initial request application message, the destination host shall act as defined in clause 7.2.1 of 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [105]. The following exceptions apply to the initial RAR/RAA command pair: - If the BM-SC supporting post-Rel-11 SGmb functionality is able to interoperate with a MBMS GW supporting Rel-11, the RAR shall include the features supported by the BM-SC within Supported-Features AVP(s) with the ‘M’ bit cleared. Otherwise, the RAR shall include the supported features within the Supported-Features AVP(s) with the M-bit set. NOTE 1: One instance of Supported-Features AVP is needed per Feature-List-ID. - If the RAR command does not contain any Supported-Features AVP(s) and the MBMS GW supports Rel-11 SGmb functionality, the RAA command shall not include the Supported-Features AVP. In this case, both BM-SC and MBMS GW shall behave as specified in the Rel-11 version of this document. - If the RAR command contains the Supported-Features AVP, the MBMS GW shall include the Supported-Features AVP in the RAA command, with the ‘M’ bit cleared, indicating only the features that both the BM-SC and MBMS GW support. NOTE 2: The client will always declare all features that are supported according to table 20.7.1. When more than one feature identifying a release is supported by both BM-SC and MBMS GW, the BM-SC will work according to the latest common supported release. Once the BM-SC and MBMS GW have negotiated the set of supported features during session establishment, the set of common features shall be used during the lifetime of the Diameter session. The table below defines the features applicable to the SGmb interface for the feature list with a Feature-List-ID of 1. Table 20.7.1: Features of Feature-List-ID 1 used in SGmb