RTCP hierarchical aggregation

The Hierarchical Aggregation (or also known as RTCP feedback hierarchy) is an optimization of the RTCP feedback model and its aim is to shift the maximum number of users limit further together with QoS measurement [1] , [2] . The RTCP bandwidth is constant and takes just 5% of session bandwidth. Therefore the reporting interval about QoS depends, among others, on a number of session members and for very large sessions it can become very high (minutes or even hours) [2] . However the acceptable interval is about 10 seconds of reporting. Bigger values would cause time-shifted and very inaccurate reported status about the current session status and any optimization made by sender could even have a negative effect to network or QoS conditions.

The Hierarchical Aggregation is used with Source-Specific Multicast where only a single source is allowed, i.e. IPTV. The another type of multicast could be Any-Source Multicast but it is not so suitable for large-scale applications with huge number of users.

Only the most modern IPTV systems use Hierarchical aggregation (June 2007).

Feedback Target

Feedback Target is a new type of member that has been firstly introduced by the Internet Draft draft-ietf-avt-rtcpssm-13 (see [4] ). The Hierarchical Aggreagtion method has extended its functionality. The function of this member is to receive Receiver Reports (RR) (see RTCP) and retransmit summarized RR packets, so-called Receiver Summary Information (RSI) [4] to a sender (in case of single level hierarchy).

Schema

Schema of hierarchicaly aggregated RTCP feedback: http://adela.utko.feec.vutbr.cz/projects/software/advanced-iptv-server-and-client-technologies/#HA_SCHEME

References

# [http://adela.utko.feec.vutbr.cz/projects/publications/#3 KOMOSNY D., NOVOTNY V. Tree Structure for Specific-Source Multicast with feedback Aggregation, in ICN07 - The Sixth International Conference on Networking . Martinique, 2007, ISBN 0-7695-2805-8]
# [http://adela.utko.feec.vutbr.cz/projects/publications/#2 NOVOTNY, V., KOMOSNY, D. Optimization of Large-Scale RTCP Feedback Reporting in ICWMC 2007. ICWMC 2007 - The Third International Conference on Wireless and Mobile Communications. Guadeloupe, 2007, ISBN: 0-7695-2796-5]
# [http://www.cl.cam.ac.uk/~jac90/NCA03.ps J. Chesterfield, E. M. Schooler. "An Extensible RTCP Control Framework for Large Multimedia Distributions"]
# [http://www.tools.ietf.org/html/draft-ietf-avt-rtcpssm-17 J. Ott, J. Chesterfield, E. Schooler. "RTCP Extensions for Single-Source Multicast Sessions with Unicast Feedback", Internet Draft draft-ietf-avt-rtcpssm-17 ]