Partial Order Transport Service: An Analytic Model

Traditional transport service is either (1) reliable and ordered (e.g., TCP) or (2) unreliable and unordered (e.g., UDP). Some new computer applications such as multimedia do not t perfectly with either of these services. Partial Order Connection (POC), a new transport-layer protocol, tries to ll the gap between (1) and (2). With POC, an application speci es a partial order (PO) for valid orderings of the packets. Packets can be transmitted or delivered by respecting any linear extension (LE) of the given PO. POC provides more generality than traditional transport protocols, which allow a user to specify the order only as a chain or an anti-chain. In POC, the reliability requirements are similarly generalized: rather than a complete guarantee as with TCP, or no guarantee as with UDP, in POC, a user speci es controlled levels of loss. Hence, POC provides partial-order and partial-reliability service. This paper presents an analytic model for POC. Results show that POC provides performance improvements over existing transport services when network service is lossy, the ratio of transmission time to propagation delay is large, or when the PO has few precedence constraints.