A Branch-Point Scheme for Multicast ABR Service in ATM Networks∗

The multicast ABR service within ATM is required to efficiently support many data applications including IP multicasting. For point-to-multipoint connections, the branch points of a multicast tree replicate cells traveling from root to leaves and consolidate feedback traveling from leaves to root [1]. The branch-point consolidation is necessary to avoid excessive backward resource management (BRM) cells and to aggregate the information from BRM cells received in the leaf-to-root direction from each branch. A number of branch-point algorithms have been proposed as in [2]–[6]. In the design of branch-point consolidation algorithms there are two major conflicting problems: consolidation delay and consolidation noise. Roberts [6] proposed a multicasting ABR branch-point algorithm with fast transient response time. In this scheme, the branch points generate a BRM cell and return it to the source when a forward resource management (FRM) cell is received from the source. The returned BRM cell conveys the minimum of the explicit rates (ER) indicated by the BRM cells received from the branches. In the previous work, it is shown that this algorithm has caused the consolidation noise problem when a returned BRM does not consolidate the feedback information from all branches [5]. To solve this problem, Siu et al. [4] proposed an algorithm without the consolidation noise. The main idea in this scheme is that a branch point passes back the BRM cell only when the BRM cells from all branches have been received. However, this algorithm suffers