Adaptive real-time group multicast

This paper shows how to provide an adaptive real-time group multicast (many-to-many) communication service. Such a service can be used by applications, like audio/video tele-conferencing, that require low loss, and bounded delay and jitter. In order to meet deterministic quality of service (QoS) requirements of a real-time group multicast, some communication resources are reserved. In this work we show (i) how bandwidth is reserved for each group, and (ii) how an active user in a multicast group can dynamically share, in an efficient and fair manner, the bandwidth allocated to its group. Quality of service support for a real-time multicast group is based on time driven priority. In this scheme the time is divided into time frames of fixed duration and all the time frames are aligned by using a global time reference which can be obtained from GPS (global positioning system). Bandwidth is allocated to a multicast group as a whole, rather than individually to each user. The allocation is done by reserving time intervals within time frames in some periodic fashion. This sort of allocation raises two problems that are studied in this paper: (1) scheduling: how time intervals are reserved to each multicast group, and (2) adaptive sharing: how the participants dynamically share the time intervals that have been reserved for their multicast group. The proposed approach is based on embedding multiple virtual rings, one for each multicast group. By using the virtual rings it is simple to route messages to all the participants, while minimizing the bound on the buffer sizes and queuing delays.