This paper describes a new protocol using explicit congestion notification (ECN) that protects hosts from the effects of multicast receivers that seek to acquire more than a fair share of network capacity. The technique is described for the IETF asynchrronous layered coding (ALC) but also extensible to other transport protocols. It provides a scalable approach that allows a chosen mediating router to determine if downstream receivers have received congestion-free packets. The protocol allows the congestion behaviour of receivers to be policed, based on the reported ECN-nonce values, knowledge of the subscription rules and synchronisation points used by the transport-layer congestion response algorithm. The reactive policing approach minimises the effects of misbehaving receivers to protect other traffic flows in the network. The method can utilise mediating routers organised in a hierarchy. This increases scalability of the solution, addresses heterogeneity in the delivery tree and assists in incremental deployment of the protocol.
- multicast transport
- layered multicast congestion control
- explicit congestion notification (ECN)
- hierarchical policing