ITU-T H.248.92 PDF

The ITU-T H.248 media gateway bearer interface protocol stack may contain principally connectionless and connection-oriented protocols. The concerned protocol layer(s) from ITU-T H.248 perspective, i.e., which are in scope of the ITU-T H.248 Stream Descriptors, are typically a network layer (L3) and higher. Connection-oriented protocols are known from L2 onwards in general, and in case of IP from L4 and higher concerning with respect to basic reference models for layered protocol architectures.

Connection-oriented protocols are characterized by explicit bearer connection control procedures, related to the establishment, modification and/or release of a bearer connection. Normally, the media gateway (MG) as slave is triggered by the master media gateway controller (MGC) for a particular bearer connection control procedure, and then autonomously executing such a procedure at the bearer interface related to a particular ITU-T H.248 termination (T)/stream endpoint (SEP).

The end-to-end bearer plane connectivity typically implies scenarios where multiple SEPs are interconnected in an ITU-T H.248 context. SEP-individual bearer control procedures are then often interlinked; e.g., an incoming bearer connection establishment procedure (at one SEP) could lead to an outgoing bearer connection establishment procedure (at a partner SEP), – at the same or at a different protocol layer.

An MGC may wish to individually control each of these procedures (so called MGC-strictly controlled mode). However, there are many use cases where the MGC could benefit from a delegation of "interlinkage work" down to the MG itself.

Such kind of behaviour is the purpose of this Recommendation.

An ITU-T H.248 package, called the "stream endpoint interlinkage" package (text codepoint 'seplink'), is defined in a generic manner, which represents a flexible tool to enable a wide range of interlinkage options.

The supported interlinkage

– is limited to a single context,

– is direction dependent,

and allows the interlinkage

– of protocol endpoints, at the same or different layers, in different SEPs ("inter-SEP interlinkage"), and

– of protocol endpoints at different layers within an individual SEP ("intra-SEP interlinkage"), and

– allows multiple interlinkage configurations to be assigned to an individual SEP.

Applicability statements

The capability of "interlinkage" relates to the MG internal forwarding of protocol control information (PCI) between different SEPs and/or different protocol layers. A layered protocol architecture is thus associated with a SEP.

The interlinkage capability is limited to protocol stack segments, which may be unambiguously described via the mechanism in clause 7.1.1.

The defined interlinkage capability is generic, i.e., applicable for all kind of connection-oriented bearer protocols. However, the focus of the initial package version is tightly coupled with protocols related to IP.