TCP Window Limiting for Asymmetric Wireless Link Throughput
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Solution Overview
Problem
Wireless transmission links, particularly in cellular networks, exhibit asymmetry between uplink and downlink bit-rates, constraining downlink performance during simultaneous upload and download due to overloaded uplink feedback, which delays acknowledgement messages and limits TCP's ability to maintain desired data transmission pace.
Innovation Solution
The method involves manipulating the TCP load in the uplink by limiting the TCP window to a fraction of the advertised window, monitoring the link asymmetry ratio, and dynamically adjusting the uplink buffer size, including selectively discarding or marking uplink TCP segments to achieve load asymmetry, thereby enhancing downlink performance without requiring changes to existing servers or protocols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TCP load in uplink is increased to utilize higher downlink capacity, then downlink throughput is improved, but uplink feedback delays increase due to overloaded uplink
Solution Approach 1:
The patent applies asymmetry by intentionally creating load asymmetry in the uplink direction to match the inherent bit-rate asymmetry of the wireless link. By limiting the TCP window in the uplink direction to a fraction of the advertised window, the system creates an artificial asymmetry that prevents uplink overload, ensuring ACK messages can be transmitted timely while still allowing the downlink to utilize its higher capacity effectively.
Solution Approach 2:
The patent changes the TCP window size parameter dynamically based on link conditions. Specifically, it limits the TCP window in the uplink direction to a fraction (e.g., 1/10th) of the advertised window when simultaneous two-way TCP traffic is detected, and adjusts the uplink buffer size accordingly. This parameter adjustment resolves the contradiction by controlling uplink load to prevent feedback delays while maintaining downlink throughput.
2Productivity
If uplink buffer size is increased to handle more TCP segments, then uplink throughput is improved, but ACK message transmission is hindered due to buffer saturation
Solution Approach 1:
The patent implements dynamic buffer management where the uplink buffer size is adjusted based on traffic conditions. When simultaneous downlink and uplink TCP traffic is detected, the uplink buffer size is reduced to a fraction of the normal size. This dynamic adjustment ensures that the buffer is large enough to handle TCP segments when needed but small enough to prevent saturation that would hinder ACK transmission, thus resolving the contradiction between uplink throughput and ACK transmission efficiency.
3Adaptability or versatility
If standard TCP protocol is used without modifications, then protocol compatibility is maintained, but downlink performance is constrained by uplink bit-rate
Solution Approach 1:
The patent introduces an intermediary function at the network layer or transport layer that sits between the standard TCP protocol and the wireless link. This intermediary monitors traffic patterns, detects simultaneous two-way TCP flows, and applies window size limitations and buffer size adjustments. By placing this intelligence at an intermediate layer, the system maintains full TCP protocol compatibility while achieving improved downlink performance through controlled load asymmetry, without requiring changes to standard TCP implementations.
Data Source
AI summary
In a method and device the TCP load offered in the uplink is manipulated such that an offered load asymmetry is achieved. Using such an arrangement it is possible to compensate for a link asymmetry when uplink and downlink connections are sharing the same uplink buffer in order to increase performance of the downlink. The method and device are capable of increasing the download performance both in the case when TCP connections are terminated in a different device than the terminal where the link layer is terminated, as well as when the TCP connections are terminated in the same device as the link-layer.