Reliable Multicast Framework

Handley has proposed a framework within which we can consider reliable multicast protocol work. In this, he describes the categories of parameters of the system:

• Number of sources: 1-to-n, n-to-m, or other.
• Transmitter start time: is there one?; is there one for each receiver marked at join time?
• Real time-Ness - what are the latency constraints on delivery of data from source to one, any or all receivers?
• consistency

He lists as non factors both congestion control and ordering, since both can be done orthogonally to the above categorisation.

He then groups applications into five main areas:

1.

Bulk Transfer (VR database, Usenet news etc)

• 1-many
• relaxed real time
• synchronised start time
• file (object) level consistency

2.

Live data feeds (stock exchange etc)

• 1 source
• no start time
• quasi real time
• may need synchronised consistency

3.

Resilient (streamed server data - like RTSP from video/audio from web site)

• 1 data source
• no start time
• stream consumed in near real time
• non consistency

4.

shared applications (wb, nte etc)

• distributed data set
• all sites fold most
• relaxed consistency
• many sources of changed

5.

Hybrid - some applications (in general, the Distributed Interactive Simulation systems) may be a hybrid of all of the above.

This is discussed further in chapter eight where we look at some applications that require particular reliable multicast semantics.