Improving SCTP Retransmission Delays for Time-Dependent Thin Streams
Springer’s Multimedia Tools and Applications 45(1-3):33-60
A large number of network services rely on IP and reliable transport pro- tocols. For applications that provide abundant data for transmission, loss is usually handled satisfactorily, even if the application is latency-sensitive. For data streams where small packets are sent intermittently, however, applications can occasionally experience extreme latencies. As it is not uncommon that such thin-stream ap- plications are time-dependent, any unnecessarily induced delay can have severe conse- quences for the service provided. It has been shown that TCP has several shortcomings with respect to the latency requirements of thin streams because of the way it handles retransmissions. As such, an alternative to TCP may be SCTP, which was de- veloped to meet the requirements of signalling transport. SCTP has subsequently been considered more appropriate than TCP for congestion-controlled streaming, primarily because SCTP maintains packetboundaries and intrinsically supports partial reliabil- ity. In this paper, we evaluate the Linux-kernel SCTP implementation in the context of thin streams. To address the identiﬁed latency challenges, we propose sender-side only enhancements that reduce the application-layer latency in a manner that is compatible with unmodiﬁed receivers. These enhancements can be switched on by applications and are used only when the system identiﬁes the stream as thin. To evaluate the latency performance, we have performed several tests over various real networks and over an emulated network, varying parameters like RTT, packet loss and amount of competing cross traﬃc. When comparing our modiﬁcations with SCTP on Linux and FreeBSD and TCP New Reno, our results show great latency improvements and indicate the need for a separate handling of thin and thick streams.
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