5.11 Messages

29.3343GPPIMS Application Level Gateway (IMS-ALG) – IMS Access Gateway (IMS-AGW)Iq InterfaceRelease 17Stage 3TS

It is recommended that IMS-AGW and IMS-ALG names are in the form of fully qualified domain name. For example the domain name of the IMS-ALG may be of the form: "ALG1.whatever.net." and the name of the IMS-AGW may be of the form: "mg1.whatever.net.".

The fully qualified domain name will be used by the IMS-AGW and IMS-ALG as part of the "Message Identifier" in the H.248 messages which identifies the originator of the message.

The IMS-ALG domain name is provisioned in the IMS-AGW or retrieved from the DNS using SRV records.

The use of a domain name provides the following benefits:

– IMS-AGWs and IMS-ALGs are identified by their domain name, not their network addresses. Several addresses can be associated with a domain name. If a command cannot be forwarded to one of the network addresses, implementations shall retry the transmission using another address.

NOTE: There are then e.g. multiple numerical address entries per single MGC entity in the "MG database of MGC entries"; see Table 5 in ITU-T H.Sup7 [29].

– IMS-AGWs and IMS-ALGs may move to another platform. The association between a logical name (domain name) and the actual platform are kept in the Domain Name Service (DNS). IMS-AGW and IMS-ALG shall keep track of the record’s time-to-live read from the DNS. They shall query the DNS to refresh the information if the time-to-live has expired.

The domain name may be used by IMS-ALG/IMS-AGW for authentication purposes.