Gateway control protocol: ITU-T H.248 Stream grouping and aggregation
|Publication Date:||1 November 2015|
As described by the ITU-T H.248 connection model (clause 6 of [ITU-T H.248.1]) a Termination sources and/or sinks one or more streams. In a multimedia conference, a Termination can be multimedia that sources or sinks multiple media streams. The ITU-T H.248 protocol uses the stream concept to model individual media flows. That is, typically, there is one media (and optional control flow) per ITU-T H.248 Stream. The characteristics of each stream are described through the use of the LocalControl, Local Descriptor (LD) and Remote Descriptors (RDs). Each Termination contains a group of streams. ITU-T H.248 makes no assumptions as to the relationship between the streams on a Termination other than indicating that streams exiting a Termination shall be synchronised with each other (clause 7.1.4 of [ITU-T H.248.1]).
Certain network technologies may require a media gateway (MG) to have knowledge of how two or more streams relate to each other beyond simply knowing that they shall be synchronised. Where there is a multiplicity of streams there may be a different relation among different sets of streams. For the purposes of this Recommendation, the relationship among streams is defined as the ''grouping semantic''. Depending on the grouping semantic the MG may be required to apply certain processing to the media related to the streams. For example: one semantic may indicate that the media is duplicated on separate streams, another semantic may indicate media is only sent on one of two streams at a time. Some grouping semantics require that media flows from multiple streams are aggregated into a single flow.
[ITU-T H.248.1] does not support a means to describe grouping semantics. This Recommendation defines the ''media grouping package'' that allows a media gateway controller (MGC) to group media from two or more ITU-T H.248 Streams according to a particular semantic and optionally to aggregate/deaggregat
The grouping framework in [IETF RFC 5888] can, in principle, be applied to any transport. It is the actual grouping stream semantics that imposes limitations, i.e., BUNDLE may only be applied to IP transports. As such, the ''media grouping package'' and the concept of an ITU-T H.248 aggregation stream can be, in principle, applied to any transport. The majority of defined stream semantics focus on IP-based transports. As such, this Recommendation describes the semantics with respect to IP. While some semantics may be used for any type of bearer technology the use of the semantics for these bearer technologies are not covered in this Recommendation.