Multipath Transport ACK Feedback for Out-of-Order Loss Recovery
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Solution Overview
Problem
In networks using multipathing, detecting packet drops is challenging due to out-of-order packet reception, leading to potential congestion and inefficient retransmission strategies.
Innovation Solution
A system and method that utilizes a receiver to track out-of-order packets and transmit acknowledgments with a packet count, allowing a transmitter to dynamically adjust retransmission thresholds based on a congestion window, thereby improving packet loss detection and recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multipathing is used to improve fabric bandwidth utilization, then network throughput increases, but packet loss detection becomes more difficult due to out-of-order arrivals
Solution Approach 1:
The patent introduces an intermediary mechanism (ACK packets with OOO counters) that mediates between the receiver's out-of-order packet tracking and the transmitter's loss detection. The receiver acts as an intermediary that processes packets out of order but provides structured feedback through ACKs, enabling the transmitter to detect losses without being confused by reordering.
Solution Approach 2:
The patent implements a feedback mechanism where the receiver sends ACK packets containing an out-of-order counter to the transmitter. This feedback allows the transmitter to understand how many packets arrived out of order and make informed decisions about retransmission, resolving the detection difficulty caused by multipathing.
2Reliability
If retransmission is performed for every potential packet loss, then reliability improves, but network congestion increases due to unnecessary retransmissions
Solution Approach 1:
The patent applies dynamics by making the retransmission threshold adaptive rather than fixed. The threshold is dynamically adjusted based on the out-of-order counter value and congestion window, allowing the system to respond to changing network conditions. This prevents unnecessary retransmissions while maintaining reliability.
Solution Approach 2:
The patent changes the parameter used for retransmission decisions from a fixed threshold to a dynamic threshold based on the out-of-order counter and congestion window. By changing this parameter adaptively, the system avoids unnecessary retransmissions that would cause congestion while still ensuring reliable delivery when needed.
3Ease of manufacture
If a fixed retransmission threshold is used, then implementation simplicity is maintained, but adaptability to varying network conditions deteriorates
Solution Approach 1:
The patent transforms the static retransmission threshold into a dynamic one that adapts to network conditions. The threshold is calculated based on the out-of-order counter and congestion window, providing adaptability while maintaining a relatively simple implementation through straightforward threshold comparison logic.
Data Source
AI summary
Embodiments herein describe tracking the number of out of order packets that have been received at a receiver (RX) from a particular transmitter (TX). In one embodiment, the RX maintains a packet tracking bitmap that starts with the expected packet sequence number (EPSN) which is the next (sequential) PSN that should be received at the RX. The RX can use acknowledgement packets to transmit the bitmap to the TX so it knows which OOO packets have been received at the RX. However, the bitmap may be too large to fit into one ACK the entire bitmap, which means segments of the bitmap may be transmitted to the TX using multiple ACKs. As such, in the embodiments herein, the RX can also include a total count of the received OOO packets in each ACK.