Router Buffer Reservation for Reliable NoC ACK Delivery
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Solution Overview
Problem
In transactional networks on chip (NoC), the receiver network interface device faces challenges in ensuring that acknowledgments (ACKs) and negative ACKs (NACKs) reach senders reliably, especially when faulty links are encountered, leading to network congestion and packet dropping.
Innovation Solution
The implementation of a buffer reservation policy for backward messages, proactive dropping of forward packets to avoid faulty links, and the use of breadcrumb tables to track forward packets and ensure reliable delivery of ACKs/NACKs.
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 along a predetermined path, but ACKs/NACKs cannot reach senders when encountering faulty links and senders cannot retransmit packets
Solution Approach 1:
The routing information is segmented into forward path information (in forward packet headers) and backward path information (in ACK/NACK packet headers). This allows independent optimization of forward and backward routing, enabling ACKs/NACKs to use alternative paths when faults are detected while maintainers source-routing for forward packets.
Solution Approach 2:
The routing path for ACKs/NACKs is made dynamic rather than static. When a faulty link is detected during forward packet transmission, the system dynamically adjusts the backward path to route ACKs/NACKs around the fault, whereas source-routing uses fixed predetermined paths.
2Reliability
If buffer space is allocated for backward messages, then ACKs/NACKs can be delivered reliably, but network congestion increases and packets may be dropped
Solution Approach 1:
Buffer space for backward messages is reserved in advance along the forward path. As forward packets traverse the network, routers pre-allocate buffer space for the corresponding ACK/NACK packets to return, ensuring reliable delivery without requiring large buffers to be available throughout the network at all times.
Solution Approach 2:
Buffer reservation is applied locally at specific routers along the forward path rather than uniformly across the entire network. Each router reserves buffer space only for backward messages passing through it, minimizing the overall buffer requirement and reducing network congestion.
Data Source
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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 reserve a memory region in a buffer for a response sent by a receiver of a forwarded packet.