Controle de Congestionamento com Suporte a ECN em Protocolos Multicast de Taxa Única

André Detsch, Marinho Barcellos

Most of the traffic that circulates through the Internet nowadays is transmitted using TCP, or Transport Control Protocol. The stability of the Internet depends on the congestion control performed by this protocol in the end nodes, as well as equivalent mechanisms (that follow the additive increase and multiplicative decrease policy) employed by other protocols. Current congestion control mechanisms are typically based on packet loss as an indication of congestion. The ECN technique (Explicit Congestion Notification), in which packets forwarded by routers are marked whenever congestion is about to occur (or already occuring), allows a transmitter to reduce the sending rate accordingly without relying on packet drops. However, ECN has not been fully explored, particularly regarding multicast protocols. This paper introduces a new congestion control mechanism for reliable multicast protocols, and extends it to incorporate and take advantage of ECN. Only single-rate and window-based protocols are considered; in such protocols, the sender maintains a sending window for each receiver. The proposed mechanism is analysed through simulations in scenarios typically employed in congestion control evaluation. Results show that the mechanism provides fairness between flows from multiple sources, and is TCP-friendly. Further, results demonstrate the substancial efficiency gain obtained with the use of ECN in multicast.

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