Root Leaf 1 Leaf 2 Upstream Downsteram : Frm : Data : Brm Branch Point

ABR Servi e Hung-Shiun Alex Chen, Klara Nahrstedt Department of Computer S ien e University of Illinois at Urbana-Champaign f hen5, klarag s.uiu .edu Abstra t The "wait-for-all" feedba k onsolidation algorithm avoids onsolidation noise, but su ers from a slow transient response. Probabilisti Aggregation and Fast Overload Indiation te hniques have been proposed to preserve the advantages of the "wait-for-all" algorithm and improve its slow transient response. However, these te hniques introdu e a new "threshold setting" problem. We developed a new onsolidation algorithm to provide a fast transient response, a low onsolidation noise and exibility in determining the threshold. In addition, we developed a dynami timeout me hanism to handle the non-responsive bran hes where the membership within a multi ast session hanges due to frequent joining/leaving of members (leaves). 1 Introdu tion The point-to-multipoint ABR (Arbitrary Bit Rate) servi e is an in reasingly important lass of servi e within ATM networks. However, supporting point-to-multipoint ABR servi e poses a number of new hallenges not en ountered in providing ABR servi e on uni ast onne tions. One of the major problems is ommonly known as the feedba k implosion problem. Resour e Management (RM) ells are used by re eivers to onvey ba k to the sour e an Expli it Rate (ER) indi ating their bandwidth fair share on the bottlene k of the path leading to them. The sour e is ontrolled to the minimum rate that an be supported by all swit hes along the path from the sour e to all leaves in the multi ast tree. Simultaneous ba kward RM (BRM) ells from all bran hes an ause an implosion at the sour e, espe ially when the number of re eivers is large. Hen e it is important for the bran h points in the multi ast tree to onsolidate the information in BRM ells re eived from downstream bran h points or re eivers and forward this onsolidated information to their upstream swit h 1. The operation of feedba k onsolidation an be explained by Figure 1. Consolidation requires synThis resear h was supported by the National S ien e Foundation Career Grant under CCR-96-23867 1The downstream dire tion from a swit h is towards the re eivers and the upstream dire tion is towards the sour e. Root Leaf 1