Fibre Channel Switch In-Order Packet Delivery Mechanism
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Solution Overview
Problem
Fibre channel networks face disruptions and packet drops due to out-of-order delivery during port channel changes, as existing mechanisms require waiting for all packets to be flushed, which is disruptive and inefficient, especially in storage area networks.
Innovation Solution
Implementing a method to block incoming packets associated with a port channel change and sending flush messages on affected links, with acknowledgments allowing packets to be unblocked, thereby ensuring in-order delivery and minimizing network disruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all packets are flushed and a wait period (e.g., 500 ms) is enforced upon detecting a port channel change, then out of order delivery is prevented, but network operation is disrupted and packet loss increases
Solution Approach 1:
The system performs preliminary actions by setting up synchronization mechanisms and sequence tracking before port channel changes occur. The primary switch tracks the sequence of packets sent and proactively manages the flushing process, allowing for controlled packet delivery without complete network halt.
Solution Approach 2:
The system implements feedback mechanisms where the primary switch receives acknowledgments from the secondary switch about packet reception status. This feedback loop allows the primary switch to make informed decisions about when to unblock packet forwarding, balancing order delivery with minimal disruption.
2Reliability
If packets are blocked during port channel changes to ensure in-order delivery, then packet delivery order is maintained, but network latency increases
Solution Approach 1:
The system blocks packets only after preliminary detection of port channel changes and only for the specific VLANs affected by the change. This targeted approach prevents unnecessary blocking of packets that would not be affected by the port channel change.
Solution Approach 2:
Instead of blocking all packets across all VLANs, the system applies blocking only to the specific VLANs experiencing port channel changes. This partial action maintains delivery order for affected traffic while allowing uninterrupted flow for unaffected traffic, minimizing overall latency.
3Reliability
If a worst-case wait period is enforced to flush all packets, then out of order delivery is prevented, but more packets are dropped than necessary
Solution Approach 1:
The primary switch receives feedback from the secondary switch regarding packet reception status and uses this information to determine when it is safe to unblock packet forwarding. This feedback-driven approach allows for precise control of the unblocking timing, minimizing packet loss while ensuring in-order delivery.
Solution Approach 2:
The system performs preliminary flushing of affected VLANs before unblocking, using sequence tracking to identify which packets have been sent and need to be flushed. This targeted flushing approach minimizes the number of packets that need to be dropped compared to a blanket worst-case approach.
Data Source
AI summary
Methods and apparatus are provided for improving fiber channel packet delivery. Techniques are provided for the in-order delivery of packets by blocking incoming packets associated with a port channel change at a fiber channel switch and sending flush messages onto links associated with a port channel change. Upon receiving acknowledgments for the flush messages, incoming packets are unblocked.