SCTP: designed for timely message delivery?
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To reduce cost and provide more flexible services, telecommunication operators are currently replacing traditional telephony networks with IP-networks. To support the requirements of telephony signaling in IP-networks, SCTP was standardized. SCTP solves a number of problems that follows from using TCP for telephony signaling transport. However, the design of SCTP is still largely based on TCP, and most of SCTP’s data transmission mechanisms are inherited from TCP. Signaling traffic has stricter requirements of timely delivery than TCP bulk traffic. However, such requirements are not supported optimally by the inherited TCP mechanisms. We therefore argue that SCTP is not fully designed for timely message delivery. In this article we present and evaluate two loss recovery adaptations that enhance the timeliness of SCTP: Early Retransmit and a modified RTO management algorithm. In addition, we evaluate an adapted Nagle-like algorithm. The results from our evaluations show a significant reduction of message delivery times. Using our loss recovery enhancements, delivery times were typically reduced with at least 30–50%. Furthermore, in some situations, message delivery times were reduced with up to 70%, using the modified Nagle algorithm. In addition to this, we evaluate all the proposals together under realistic conditions, with very good results.
KeywordsSCTP Transport protocols IP-networking Network emulation Loss recovery
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