Router Packet Management via Breadcrumb Tables
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Solution Overview
Problem
In transactional networks on chip (NoC), acknowledgments (ACKs) and negative acknowledgments (NACKs) may not reach senders due to faulty links, leading to packet retransmission issues and network congestion, as routers cannot select alternative paths to bypass faulty links, resulting in dropped packets and inefficient network operation.
Innovation Solution
Implementing a buffer reservation policy and selective packet dropping mechanisms, including breadcrumb tables, fault prediction, and reservation policies for backward messages, to ensure buffer space for backward packets and prevent packet drops due to congestion or faulty links, allowing routers to proactively avoid faulty paths and maintain in-order packet delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source-routing is used to encode the entire routing path in packet headers, then packets can be delivered reliably through the network, but ACKs/NACKs cannot reach senders when encountering faulty links because routers cannot select alternative paths
Solution Approach 1:
The routing path is segmented into forward path and backward path. Forward packets use source-routing with encoded paths in headers, while backward ACKs/NACKs use a different mechanism where routers maintain breadcrumb tables to track the reverse path, enabling independent path selection for responses.
Solution Approach 2:
Routers act as intermediaries that maintain breadcrumb tables to record the forward path. When faulty links are detected, these intermediate routers can use the breadcrumb information to reroute ACKs/NACKs through alternative paths, mediating between the source-routing constraint and the need for adaptive rerouting.
2Device complexity
If routers cannot select alternative paths to bypass faulty links, then source-routing remains simple to implement, but network congestion increases and packets are dropped
Solution Approach 1:
Routers perform preliminary actions by maintaining breadcrumb tables that record the forward path before faults occur. When a faulty link is detected, the preliminary breadcrumb information enables rapid computation of alternative backward paths without requiring complex real-time routing decisions.
Solution Approach 2:
The routing system transitions from static source-routing for forward packets to dynamic adaptive routing for backward packets. Routers dynamically select alternative paths for ACKs/NACKs based on detected faults, while maintaining the simplicity of source-routing for the primary data transmission direction.
3Quantity of substance
If buffer space is not reserved for backward packets, then router memory usage is reduced, but packets are dropped due to congestion when ACKs/NACKs need to be transmitted
Solution Approach 1:
Buffer space is allocated with local quality differentiation: forward packets use standard buffering, while backward packets (ACKs/NACKs) receive prioritized buffer reservations. This ensures that critical response packets have guaranteed memory space, improving reliability without uniformly increasing overall buffer capacity.
Data Source
AI summary
Examples described herein relate to a router. In some examples, the router includes an interface and circuitry coupled to the interface. In some examples, the circuitry is to: based on receipt of a negative acknowledgement (NACK) message: record an endpoint destination of a packet corresponding to the NACK message in a data allocated per-link and drop a second packet transmitted to the endpoint destination corresponding to the NACK message to drop the second packet one or more hops before reaching a congested device.