Deterministic Packet Marking for Congestion Price Estimation

Richard W. Thommes, Mark Coates

Abstract: Several recent price-based congestion control schemes require relatively accurate path price estimates for successful operation. The proposed addition of the two-bit explicit congestion notification (CCN) field in the IP header provides routers with a mechanism for conveying price information. Recently, two proposals have emerged for probabilistic packet marking at the routers; the proposals allow receivers to estimate path price from the fraction of marked packets. In this paper we introduce an alternative deterministic marking scheme for encoding path price. Under our approach, each router quantizes the price of its outgoing link to a fixed number of bits. We then make use of the IP identification (IPid) field to map data packets to different probe types, and each probe type calculates a partial sum of the path price bits. A router deduces its marking behaviour according to the IPid and the TTL (time to live) field of each packet. We evaluate the performance of our algorithm in terms of its error in representing the end-to-end price, and compare it to probabilistic marking. We show that based on empirical Internet traffic characteristics, our algorithm performs better when estimating path price using small blocks of packets. We also derive the probability distribution of the error for our scheme, and provide a relatively simple bound on its maximum mean-squared error.