Link State Packet Flooding Order for Faster Convergence
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Solution Overview
Problem
In IS-IS protocol networks, the flooding of Link State Packets (LSPs) often results in delayed connectivity map construction and routing path discovery due to the unordered or inefficient ordering of LSPs, leading to prolonged convergence times for nodes, especially when nodes far away from the source have larger system IDs.
Innovation Solution
LSPs are flooded in an order related to the relative costs of paths from the source node, with the source node's LSP sent first, followed by others in ascending order of their costs, using a cost table or data structure to continuously update and prioritize LSPs based on their paths to the receiving node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LSPs are flooded in ascending order by system ID, then LSPs with smallest IDs are sent first, but nodes far away with large system IDs cannot compute SPT until all LSPs are received
Solution Approach 1:
The patent applies preliminary action by having the source node send its own LSP first (with cost 0) before sending other LSPs. This preliminary transmission of the source node's LSP enables receiving nodes to immediately begin computing shortest paths to the source node, rather than waiting for all LSPs to arrive. The source node's LSP is prepared and transmitted in advance, allowing immediate SPT computation for the source node while other LSPs are still being received and processed.
2Productivity
If LSPs are flooded in no particular order, then flooding may occur quickly, but nodes may receive LSPs from far away nodes before receiving source node's LSP
Solution Approach 1:
The patent applies parameter changes by ordering LSP transmissions based on path cost parameters rather than system ID or random order. The source node determines the cost associated with each path to other nodes and transmits LSPs in ascending order of these costs. This parameter-based ordering ensures that LSPs with lower path costs (which are more critical for SPT computation) are transmitted first, improving both efficiency and reliability of path discovery.
3Measurement precision
If nodes wait for all LSPs before computing SPT, then complete connectivity information is available, but convergence is prolonged
Solution Approach 1:
The patent enables preliminary SPT computation by ensuring the source node's LSP is transmitted first. Receiving nodes can immediately compute the shortest path to the source node using this LSP, rather than waiting for all other LSPs to arrive. This preliminary computation provides immediate routing capability to the source node while allowing incremental updates as additional LSPs are received and processed.
Data Source
AI summary
Disclosed are methods and apparatus for flooding link state packets or packet data units (LSP's) from a first node to one other LSP receiving node, where the LSP's are flooded in an order that is related to relative costs of various paths emanating from the first node. That is, the first node sends its own LSP first since the first node has no cost relative to itself. The first node then sends other LSP's that are associated with a plurality of other LSP sending nodes that have previously flooded their LSP's to the first node, and these other LSP's are sent by the first node to the other LSP receiving node in an order related to the relative costs associated with the paths from the first node to each of the other LSP sending nodes which had previously sent the other LSP's to the first node.