TCP Fast Retransmit Duplicate ACK Comparison
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Solution Overview
Problem
Conventional TCP congestion control methods, such as Newreno, often result in retransmission timeouts due to high segment loss rates, leading to decreased transmission performance and wastage of bandwidth, as they rely on a long timeout period and reduce the congestion window, making it difficult to receive sufficient duplicate ACKs for retransmitting lost segments.
Innovation Solution
Implementing a Fast Retransmit and Fast Recovery mode in TCP communication systems, where the transmission terminal calculates and compares the number of received duplicate ACKs with the expected number, and retransmits lost segments if the accumulated duplicate ACKs exceed the expected, along with initializing a recovery sequence number to determine the end of the Fast Recovery mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmission terminal uses conventional TCP congestion control (Newreno) with long timeout periods, then reliability is maintained through timeout-based retransmission, but transmission performance deteriorates and bandwidth is wasted due to prolonged waiting times
Solution Approach 1:
The patent applies preliminary action by proactively retransmitting segments before the timeout period expires. When three duplicate ACKs are received, the transmission terminal immediately retransmits the lost segment without waiting for the timeout timer to expire. This anticipatory retransmission eliminates the unnecessary waiting time while maintaining reliable delivery, directly resolving the contradiction between reliability and time loss.
2Object-affected harmful factors
If the transmission terminal reduces the congestion window size upon retransmission, then network congestion is controlled, but the terminal fails to receive sufficient duplicate ACKs to trigger retransmission of recently lost segments
Solution Approach 1:
The patent applies dynamics by making the congestion window adjustment conditional rather than automatic. Instead of reducing the congestion window for every retransmission event, the terminal dynamically adjusts the window size only when congestion is actually detected through the duplicate ACK mechanism. This dynamic approach ensures that the congestion control mechanism remains effective while preserving the ability to detect and retransmit lost segments reliably.
3Productivity
If the transmission terminal continuously transmits new segments after retransmitting a lost segment, then throughput is improved, but the terminal cannot receive sufficient duplicate ACKs to detect subsequently lost segments
Solution Approach 1:
The patent applies feedback by using duplicate ACKs as a detection mechanism for lost segments. When three duplicate ACKs are received, the terminal infers that a segment is lost and triggers retransmission. This feedback loop allows the system to maintain high throughput by quickly recovering from losses without sacrificing reliability, as the duplicate ACK feedback provides timely information about segment delivery status.
Data Source
AI summary
A congestion control method and system in a communication system that transmits and receives a data segment using Transmission Control Protocol (TCP) and performs a Fast Retransmit mode and a Fast Recovery mode upon occurrence of a lost segment. A transmission terminal retransmits the lost segment to a reception terminal and then calculates the expected number of duplicate acknowledgements (ACKs) expected to be received from the reception terminal. The transmission terminal determines whether an ACK recently received from the reception terminal is identical to a new ACK or a duplicate ACK. The transmission terminal accumulates the received duplicate ACK, and compares the number of the accumulated duplicate ACKs with the expected number of the duplicate ACKs. The transmission terminal retransmits the lost segment to the reception terminal if the number of the accumulated duplicate ACKs is larger than the expected number of the duplicate ACKs.