TCP Proxy for HF Radio Link Stability
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Solution Overview
Problem
Transmission Control Protocol (TCP) connections often fail on wireless links, such as High Frequency (HF) radio links, due to long and variable latency, leading to excessive retransmissions and timeouts, as the TCP algorithm does not accurately estimate the Round Trip Time (RTT) and fails to adapt to high error rates and congestion.
Innovation Solution
A TCP proxy system that intercepts IP packets, sends simulated acknowledgements to the sender, and buffers data packets to estimate the actual RTT by increasing the delay time of simulated acknowledgements until it matches the actual RTT, thereby reducing the likelihood of TCP timeouts and improving communication reliability on high-latency links.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TCP is used for data transmission on wireless links, then data delivery reliability is improved, but connection timeouts and transfer failures occur due to long and variable latency
Solution Approach 1:
The system performs preliminary action by sending simulated acknowledgements before the actual RTT expires. The TCP proxy sends simulated ACKs at calculated intervals based on estimated RTT, preventing the sender from timing out before data is actually delivered through the wireless link.
Solution Approach 2:
The TCP proxy acts as an intermediary between the TCP sender and the wireless link. It intercepts TCP segments, sends simulated acknowledgements to the sender, and separately transmits data through the wireless link, decoupling the TCP timeout mechanism from the actual wireless transmission time.
2Loss of time
If TCP proxy sends simulated acknowledgements immediately, then connection timeout is reduced, but RTT estimation accuracy deteriorates
Solution Approach 1:
The system uses dynamic RTT estimation that adapts over time. The proxy calculates initial RTT from actual acknowledgements received from the wireless link, then uses this estimate to determine simulated ACK timing, continuously refining the estimation as more data is transmitted.
Solution Approach 2:
The system implements feedback by using actual RTT measurements from wireless link acknowledgements to inform the timing of simulated acknowledgements. The proxy monitors the relationship between sending simulated ACKs and receiving actual ACKs from the wireless link, adjusting its RTT estimate based on this feedback loop.
3Productivity
If data transmission rate is increased on wireless links, then throughput is improved, but error rates increase causing retransmissions
Solution Approach 1:
The TCP proxy serves as an intermediary that buffers data before transmission over the wireless link. It decouples the high-speed data generation from the error-prone wireless transmission, allowing the sender to transmit at high rates while the proxy manages retransmissions based on actual link conditions.
Data Source
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AI summary
A communications system includes a sender device configured to send data packets in accordance with a Transmission Control Protocol (TCP) to a receiver device. An intermediate device is coupled between the sender device and the receiver device and includes a wireless transceiver configured to provide a communications link between the sender device and the receiver device and wherein said communications link is susceptible to at least one of transmission delays and transmission errors. A controller is coupled to the wireless transceiver and configured to serve as a TCP proxy between the sender device and the receiver device by sending successive simulated TCP acknowledgements of delivery to the sender device starting at a delay time shorter than a TCP retransmission timeout period and increasing for each successive simulated TCP acknowledgement.