The relationship between functional entities for the interface at the W1 reference point, between the WWSF and the UE, the interface at the W2 reference point, between the eP-CSCF and the UE, the interface at the W3 reference point, between the UE and the eIMS-AGW, and the interface at the W4 reference point, between the WWSF and the WAF, are defined in Annex U
of TS 23.228
The relationship between the functional entities for interface at the Mw reference point, between the eP-CSCF and the remainder of the IP multimedia core network subsystem, is defined in TS 23.228
A number of appropriate mechanisms exist for signalling communication between the WIC and the eP-CSCF. Sucessful use of a mechanism other than those specified in this document will require some form of prior agreement between the operator of the WWSF and the operator of the eP-CSCF, as to the nature of the signalling mechanism that is to be adopted, and therefore the interworking required at the eP-CSCF. The mechanism of prior agreement and the nature of such agreement is not defined in this document.
A signalling transport mechanism for SIP is standardised in this release of this document, i.e. SIP over websockets (see RFC 7118
), but this is not a mechanism that has to be supported by all eP-CSCFs.
When SIP over websockets is used, it can be appropriate for the SIP used to conform to the definitions for SIP on the Gm reference point as specified in TS 24.229
. Such a requirement is not mandatory, but where other SIP mechanisms are used:
the usage will require some form of prior agreement with the operator of the eP-CSCF, as to the nature of the signalling mechanism that is to be adopted; and
the SIP mechanisms will have to enable the eP-CSCF to conform to the SIP requirements over the Mw reference point to the remainder of the IP multimedia core network subsystem as specified in TS 24.229.
SDP is used for the signalling session information between the WIC and the eP-CSCF. Such SDP conforms to requirements for SDP on the Gm reference point.