Byte-Based Credit Flow Control for Lossless Packet Buffering
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Solution Overview
Problem
Existing data communications infrastructure faces challenges in scaling bit rate while maintaining lossless operation, particularly due to increased bandwidth and latency requirements, which are exacerbated by the need for substantial headroom in packet buffers to prevent congestion and packet drops, limiting the number of lossless classes of services that can be enabled on a link.
Innovation Solution
A byte-based credit flow control mechanism is introduced, where the sender maintains a buffer state at the receiver using byte-expansion information to adjust a credit counter, allowing for efficient packet buffer management and eliminating the need for substantial headroom by being insensitive to packet storage methods and self-synchronizing, enabling lossless operation without relying on worst-case scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional time-based flow control schemes are used, then packet buffer headroom is increased to prevent congestion, but the number of lossless classes of services that can be enabled on a link is limited
Solution Approach 1:
The patent changes the flow control parameter from time-based to byte-based credit counters. Instead of using time quanta to control packet flow, the system uses byte-count credits that directly track buffer usage. This parameter change allows for more granular and accurate buffer management, enabling multiple lossless classes of services to share buffer resources without requiring excessive headroom for each class.
Solution Approach 2:
The patent segments the packet buffer into multiple classes of service with separate credit counters for each class. Each class maintains its own credit counter that tracks available buffer space independently. This segmentation allows different classes of traffic to be managed separately, enabling multiple lossless services to operate simultaneously without interfering with each other, while efficiently utilizing the total buffer capacity.
2Reliability
If substantial headroom is allocated in packet buffers to prevent congestion and packet drops, then lossless operation is maintained, but buffering requirements increase
Solution Approach 1:
The patent implements feedback through credit counters that continuously track the actual usage of packet buffer space by each class of service. The receiver monitors buffer occupancy and sends credit updates to the sender, providing real-time feedback on available buffer space. This feedback mechanism allows the system to dynamically adjust transmission rates based on actual buffer conditions rather than allocating excessive static headroom, thereby maintaining lossless operation with reduced buffering requirements.
Solution Approach 2:
The patent uses preliminary action by pre-configuring credit counters with the total buffer capacity allocated to each class of service. These credit counters are initialized before traffic flow begins, establishing the maximum credit limit in advance. As packets are transmitted and buffered, credits are decremented accordingly. This preliminary setup eliminates the need for additional dynamic headroom allocation during operation, as the credit counters inherently prevent buffer overflow by tracking usage against pre-established limits.
3Productivity
If credit-based flow control with byte-expansion information is implemented, then throughput is increased with reduced buffering, but the system complexity increases
Solution Approach 1:
The patent applies self-service by having each endpoint (sender and receiver) independently maintain and update its own credit counters based on local buffer state and transmitted/received packet counts. The receiver autonomously monitors its buffer occupancy and generates credit updates when buffer space becomes available. The sender independently tracks its transmitted byte count and adjusts its transmission rate based on received credits. This self-service approach eliminates the need for complex centralized control or extensive handshaking protocols, simplifying the overall system while enabling high throughput through efficient buffer utilization.
Data Source
AI summary
A system and method for credit-based link level flow control. In one embodiment, a byte-based flow control mechanism is based on a sender effectively maintaining a buffer state at the receiver. In maintaining a buffer state at the receiver, the sender is provided with information regarding byte expansion at the receiver. This byte-expansion information can be used by the sender to identify the amount of additional storage needed by the receiver when storing a packet transmitted by the sender in the receiver's packet buffer.