Delay-Based Congestion Controller SRTT Smoothing
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Solution Overview
Problem
Cellular wireless networks experience higher packet loss and longer round trip times due to delay jitter caused by layer 2 retransmission mechanisms, leading to incorrect congestion handling and potential over-aggression in delay-based congestion control.
Innovation Solution
An apparatus and method that determine minimum and maximum smoothed round trip time (SRTT) values using exponential moving average functions to improve throughput control during delay-based congestion, allowing for a more accurate congestion window calculation and reducing the impact of delay jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If delay-based congestion control is used in cellular wireless networks, then throughput control is improved, but incorrect congestion handling occurs due to delay jitter from layer 2 retransmission mechanisms
Solution Approach 1:
The patent introduces an intermediary mechanism (smoothed RTT calculation using exponential moving average) that mediates between the raw RTT measurements affected by delay jitter and the congestion control decisions. This intermediary filtering process removes the harmful delay jitter components while preserving the true congestion signal, allowing accurate congestion handling to be achieved.
Solution Approach 2:
The patent implements feedback by continuously monitoring RTT values and using exponential moving average to smooth out variations. The smoothed RTT feedback is then used to adjust congestion window size, creating a closed-loop control system that adapts to network conditions while filtering out noise from layer 2 retransmissions.
2Device complexity
If conventional RTT measurement is used, then simplicity is maintained, but accuracy deteriorates due to delay jitter causing incorrect differentiation between congestion and delay jitter
Solution Approach 1:
The patent changes the parameter representation by transforming raw RTT measurements into smoothed RTT values using exponential moving average with a smoothing factor. This parameter transformation filters out high-frequency variations caused by delay jitter while maintaining the underlying trend, thereby improving measurement precision without significantly increasing complexity.
3Speed
If delay-based congestion control reacts to all RTT variations, then responsiveness is improved, but over-aggression occurs leading to unnecessary retransmissions
Solution Approach 1:
The patent applies partial action by using a smoothing factor in the exponential moving average that partially filters RTT variations. Instead of reacting to all RTT changes, it selectively responds to sustained increases in RTT that indicate true congestion, while ignoring transient variations caused by delay jitter, thus avoiding unnecessary retransmissions.
Data Source
AI summary
An apparatus and method of providing improved throughput on delay-based congestions comprising a packet engine and a delay-based congestion controller are provided. The packet engine detecting a delay jitter that is caused by a layer 2 retransmission of a data packet, is configured to measure a round trip time (RTT) value. The delay-based congestion controller is configured to receive the RTT value and to determine a smoothed RTT (SRTT) value using the RTT value and one or more moving average functions. The delay-based congestion controller is also configured to, if the SRTT value is smaller than a set minimum SRTT value, assign the SRTT value to the set minimum SRTT value. The delay-based congestion controller is further configured to, if the SRTT value is larger than a set maximum SRTT value, assign the SRTT value to the set maximum SRTT value.