Enhancing TCP Performance Over Satellite Channels
Abstract
In general the Transmission Control Protocol (TCP) works well while establishing end-to-end connections for common Internet services. However, there are two problem areas associated with performance over satellite channels: propagation delay and channel noise effects. Noise is a common problem in wireless technologies and consequently the bit-error-rate (BER) is significantly higher than in wired networks. TCP is particularly vulnerable to BER because it is a reliable protocol. TCP will retransmit lost or corrupted data when errors are detected. However, the main design goal was to avoid congestion-collapse in networks. The protocol has no means to decide whether a loss event was caused by congestion (buffer-overflow) or by corruption (noise, jamming). Nevertheless, TCP should react in a different way, depending on the type of errors: it should immediately retransmit outstanding data if the loss was caused by noise, and it should reduce network traffic if congestion was the reason for dropping data-packets. Currently every loss indicates network congestion for the TCP standard version defined in RFC 0793. As a result it will reduce its sending rate significantly by invoking congestion control algorithms, regardless of the source of errors. TCP is a "Sliding Window" protocol that uses acknowledgements to verify proper data delivery. Such protocols allow the sender to transmit only a given amount of data before receiving an acknowledgement in return. After each acknowledgement the window size is increased and a larger number of segments will be transmitted. The time TCP needs to reach maximum throughput is a function of the time needed for delivery and acknowledgement of data. It is obvious that long delays will hurt performance on links characterized by a large bandwidth-delay-product. In this case TCP will poorly utilize the available bandwidth. Furthermore, long delays increase the amount of time TCP spends to recover from losses while throughput is already
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2000
- Accession Number
- ADA385294
Entities
People
- Hugues Latour
- Maik Kammermann
Organizations
- Defence Research and Development Canada