Selective Acknowledgment for Out-of-Order Packet Retransmission
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Solution Overview
Problem
Current data transmission methods in lossy networks, particularly for remote direct memory access (RDMA) over converged Ethernet (RoCE) version 2, struggle to efficiently handle packet loss and delay due to inefficiencies in distinguishing between dropped and delayed packets, leading to suboptimal performance.
Innovation Solution
Implementing a selective acknowledgment (SACK) mechanism that provides detailed information about received and missing packets, including sequence numbers, arrival times, and path information, allowing the requester device to make informed retransmission decisions based on this data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional packet retransmission methods are used in lossy networks, then network simplicity is maintained, but packet loss handling efficiency deteriorates
Solution Approach 1:
The patent implements selective acknowledgment (SACK) where the responder device sends feedback information to the requester device about which packets were received and which were lost. This feedback mechanism enables the requester to make informed retransmission decisions, significantly improving packet loss handling efficiency while maintaining reasonable system complexity through structured feedback protocols.
Solution Approach 2:
The patent segments the packet stream into individual packets with unique sequence numbers, allowing the responder to identify and acknowledge specific packets independently. This segmentation enables selective retransmission of only lost packets rather than resending the entire data stream, thereby improving efficiency without requiring complex full-stream retransmission mechanisms.
2Productivity
If packets are resent upon timeout, then implementation simplicity is maintained, but network communication efficiency deteriorates
Solution Approach 1:
The SACK mechanism provides the requester with detailed feedback about packet delivery status, including which packets were received successfully and which were lost or delayed. This feedback eliminates the need for simple timeout-based retransmission decisions, enabling the requester to efficiently identify and retransmit only the problematic packets, thereby improving network communication efficiency while maintaining operational simplicity through clear feedback protocols.
Solution Approach 2:
The responder device performs preliminary actions by collecting and organizing packet status information before the timeout period expires. By proactively identifying and reporting lost packets through SACK, the system prepares retransmission decisions in advance, improving communication efficiency without requiring complex real-time decision-making during timeout scenarios.
3Measurement precision
If traditional acknowledgment methods are used, then protocol simplicity is maintained, but packet loss distinction accuracy deteriorates
Solution Approach 1:
The patent enhances traditional acknowledgment methods by implementing SACK, which provides detailed feedback about individual packet delivery status. The responder sends acknowledgment information that specifically identifies which packets were received and which were lost, enabling accurate distinction between dropped and delayed packets. This feedback mechanism improves measurement precision while maintaining reasonable complexity through structured acknowledgment protocols.
Solution Approach 2:
The patent segments the acknowledgment process into individual packet-level acknowledgments rather than using simple cumulative ACKs. Each packet receives individual attention in the SACK mechanism, allowing precise identification of which specific packets were lost. This segmentation approach improves dropped packet identification accuracy without requiring overly complex acknowledgment processing, as each segment can be handled independently.
4Reliability
If out-of-order packets are not handled, then processing simplicity is maintained, but data transmission reliability deteriorates
Solution Approach 1:
The patent segments packets into individually trackable units with unique sequence numbers, enabling the responder to identify and acknowledge specific packets regardless of their arrival order. This segmentation allows the system to handle out-of-order packets reliably by processing each segment independently, improving data transmission reliability without requiring complex reordering algorithms, as the segmented approach naturally accommodates various packet arrival scenarios.
Solution Approach 2:
The SACK mechanism provides feedback that specifically tracks individual packet delivery status, enabling the requester to understand which packets were received out-of-order and which were lost. This feedback enables the requester to make informed retransmission decisions for out-of-order packets, improving reliability while maintaining processing simplicity through clear packet-by-packet status information that guides retransmission actions without complex processing requirements.
Data Source
AI summary
In one embodiment, a responder device includes a network interface to receive packets of a stream of packets transmitted from a requester device with packet sequence numbers, and packet processing circuitry to collect information about the packet sequence numbers of the packets that have been received from the requester device, generate a selective acknowledgement including an indication of the packet sequence numbers of at least one packet of the packets that has been received and at least one other packet of the packets that has not been received by the responder device from the requester device, wherein the at least one packet that has been received by the responder device includes at least one of the packets received out-of-order according to the packet sequence numbers, and send the selective acknowledgement to the requester device via the network interface.