Segment Routing Path Computation Optimizing Label Stack Size
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Solution Overview
Problem
In segment routing networks, path computation that meets specific constraints such as delay and bandwidth requirements often results in a large label stack, which exceeds the maximum size limits imposed by routers, making it difficult to define acceptable paths.
Innovation Solution
A method and apparatus for determining a segment identifier-optimised path by analyzing a modified network topology that includes a subset of nodes and virtual links, allowing for a reduced label stack while meeting constraints, and outputting segment identifiers that define the path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a path is computed to meet constraints such as delay and bandwidth, then the path quality is improved, but the label stack size increases and may exceed router limits
Solution Approach 1:
The network path is segmented into multiple sections, each identified by a segment identifier (SID). Instead of listing every individual link in the path, the path is divided into segments that can be represented by fewer labels. This segmentation allows the path to meet constraints while reducing the label stack size by grouping multiple links under single segment identifiers.
Solution Approach 2:
A path computation entity (PCE) acts as an intermediary that computes the optimized path and generates the segment identifier stack. The PCE analyzes network topology and constraints, then produces a compact SID representation that satisfies both the path constraints and router label stack limits, mediating between the constraint requirements and the routing equipment capabilities.
2Adaptability or versatility
If the label stack size is reduced to meet router limits, then device compatibility is improved, but the ability to meet path constraints may be compromised
Solution Approach 1:
The invention changes the representation parameters of the path from detailed link-by-link identification to compressed segment identifier representation. By transforming the path description into a different parameter format (SIDs that encode multiple links), the system achieves both reduced label stack size and maintained constraint satisfaction capability.
Solution Approach 2:
The path computation entity performs preliminary analysis of the network topology and constraints before generating the path. By pre-computing the optimized segment identifier stack that satisfies both constraints and size limits, the system prepares the solution in advance, ensuring both router compatibility and constraint fulfillment without needing to compromise either requirement.
3Productivity
If the network size increases, then network capacity is improved, but the complexity of path computation and label stack management increases
Solution Approach 1:
The network is viewed as a collection of segments identified by SIDs, which remain manageable even as network size grows. This segmentation approach allows the path computation to focus on selecting relevant segments rather than managing individual links, reducing computation complexity while supporting network expansion.
Solution Approach 2:
Segment identifiers serve multiple functions: they identify network segments, encode path information, and provide constraint validation. This multi-functionality reduces the overall complexity of path computation in large networks by consolidating multiple management tasks into a unified SID-based framework that scales with network size.
Data Source
AI summary
A method of path computation in a segment routing network, the network comprising a set of nodes. The method comprises receiving a request for computation of a path between end nodes in the network, the request including a constraint. The method further comprises determining a segment identifier-optimised path defined by a stack of one or more segment identifiers, wherein the segment identifier-optimised path meets the constraint. The determining of the segment identifier-optimised path comprises analyzing a topology of the network comprising: at least a sub-set of the nodes, links between adjacent nodes indicative of possible paths between the nodes, and virtual links between pairs of nodes indicative of possible paths between the pairs of nodes. The method further comprises outputting at least one segment identifier which defines the determined path.