scope:

In a split media gateway controller (MGC) and media gateway (MG) environment, call-level application level gateways (ALGs) are common in order to translate address information (i.e., network address and port translation (NAPT)) between two signalling domains. Typically, the application signalling traverses the MGC. ITU-T H.248 is therefore not involved in these translations other than to set the necessary media transport parameters on applicable Terminations.

Increasingly bearer-level application control signalling is being used which instead traverses the MG. This bearer-level application signalling typically is used within a session that has been established by the MGC; thus, some coordination between the two levels is needed.

This Recommendation provides functionality that allows the MGC and MG to coordinate bearer-level application level gateway functionality. By transporting bearer-level application protocols between the MGC and MG using ITU-T H.248 signalling (a method known as "backhauling"), it allows the MGC access to the bearer-level application protocol.

This Recommendation also supports the ability to use an alternative method to identify the bearer-level application protocol on an ITU-T H.248 Stream. The "MG located Bearer Level ALG" package allows an MG to autonomously act as an application level gateway and modify address information.

This Recommendation also contains an annex that describes Extensible Messaging and Presence Protocol (XMPP) to MSRP interworking utilising mechanisms defined in this Recommendation.