Intra Switch Transport Protocol Sliding Window Mechanism
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Solution Overview
Problem
Current arbitration schemes in data switches result in high latency due to the request-grant loop latency, where ingress devices must wait for acknowledgments before transmitting data packets, leading to congestion and increased packet latency.
Innovation Solution
Implementing a transport protocol that allows ingress devices to send data packets without waiting for initial acknowledgments, using a sliding window mechanism based on bandwidth and round trip time, with the egress device controlling the acknowledgment rate to maintain output buffer occupancy and prevent congestion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If arbitration schemes are used to regulate data flows in switches, then data transmission control is improved, but packet latency increases due to request-grant loop latency
Solution Approach 1:
The patent implements a sliding window mechanism that pre-allocates transmission windows to ingress devices before data transmission begins. This allows ingress devices to send data packets immediately within their allocated windows without waiting for real-time acknowledgments, effectively performing the grant action in advance and eliminating request-grant loop latency.
Solution Approach 2:
The egress device sends acknowledgment messages back to ingress devices to inform them of buffer occupancy status and window allocation. This feedback mechanism allows the system to maintain reliable flow control while enabling ingress devices to proactively adjust their transmission rates based on received acknowledgments, reducing waiting time without sacrificing transmission control.
2Loss of time
If immediate packet transmission is allowed without waiting for acknowledgments, then latency is reduced, but congestion may occur at inputs, outputs, or crossbar
Solution Approach 1:
The patent implements dynamic window allocation where the size and number of transmission windows are adjusted based on real-time buffer occupancy status. The egress device dynamically controls the acknowledgment rate to match the fabric's ability to handle incoming traffic, allowing immediate transmission when capacity is available while automatically preventing congestion when buffers are full.
Solution Approach 2:
Ingress devices are pre-informed of their transmission windows through acknowledgment messages before they need to send data. This preliminary allocation of transmission capacity allows devices to send immediately without waiting, while the pre-planned window limits prevent overloading the fabric and causing congestion.
3Reliability
If acknowledgment rate is controlled to maintain buffer occupancy, then congestion is prevented, but transmission efficiency may be reduced
Solution Approach 1:
The sliding window mechanism ensures continuous transmission by pre-allocation of windows and allowing ingress devices to send data immediately upon window availability. The acknowledgment rate is controlled to maintain continuous buffer occupancy without empty waste space, ensuring that the fabric is continuously utilized at optimal capacity without causing congestion, thus maintaining high transmission efficiency while preventing congestion.
Data Source
AI summary
In one implementation, a network device is configured to implement an intra switch transport protocol. The intra switch transport protocol is configured to determine a maximum window size according to a predetermined bandwidth and a round trip time between a plurality of ingress ports and an egress port. The network device is configured to calculate an assigned window value for the one of the plurality of ingress ports based on the maximum window size and generate an acknowledgment message including the assigned window value for the one of the plurality of ingress ports, and to delay successive acknowledgement messages according to fabric congestion and egress port occupancy.