Improving TCP/IP performance for the land mobile satellite channel

Satellite communications systems are an important part of the infrastructure for many commercial and military networks. There is a great deal of interest in seamlessly extending terrestrial IP networks via satellite. Unfortunately, the higher bit error rate (BER) and bandwidth delay product (BDP) of the satellite channel result in low channel utilization and reduced throughput for TCP traffic. The Wireless Networking Testbed at Lincoln Laboratory was developed to evaluate the performance of TCP/IP and potential protocol enhancements under realistic channel conditions. This paper extends the results presented in Stadler et al. (1999) to the land mobile satellite channel using the digital model presented by Lutz and Cygan (1991). The channel model, based on a two-state Markov chain, produces random bit errors under the assumption of Rician (non-blocking) or Rayleigh (blocking) signal statistics. The model parameters include signal-to-noise ratio (SNR), bit rate, velocity, and environment type (i.e., urban, highway, etc.). TCP behavior is characterized for selected values of the channel parameters under a variety of testbed configurations. Test results indicate that fading losses contribute to substantial performance degradation for TCP, even when the selective acknowledgement (SACK) option is enabled. In addition, two protocol enhancement techniques, a link layer protocol and the Wireless IP Suite Enhancer (WISE), are evaluated.