IS-IS TLV MSD Advertisement for Segment Routing Path Computation
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Solution Overview
Problem
In Segment Routing networks, existing methods fail to effectively communicate the maximum Segment Identifier Depth (SID) of network elements to controllers, leading to potential network congestion and failures due to the inability to report MSD values without using Path Computation Element Communication Protocol (PCEP) or Border Gateway Protocol (BGP), which limits path utilization and wastes capabilities of network devices.
Innovation Solution
The method involves transmitting a Type Length Value (TLV) element containing a Maximum Segment Identifier Depth (MSD) value using Intermediate System to Intermediate System (IS-IS) protocol, allowing network elements to advertise their MSD values directly to controllers, enabling the determination of suitable paths that do not exceed their SID insertion capabilities, thereby avoiding network issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCEP or BGP protocol is used to report MSD values, then network elements can communicate their maximum SID depth to controllers, but the system complexity increases and path computation efficiency decreases
Solution Approach 1:
The patent uses IS-IS protocol as an intermediary mechanism to advertise MSD values through routing information exchange, avoiding the need for dedicated PCEP or BGP communication channels. The IS-IS protocol acts as a mediator that carries MSD information within existing routing update messages, thereby reducing system complexity while maintaining reliable communication of capability information.
Solution Approach 2:
The IS-IS routing protocol is made multi-functional by enabling it to carry both traditional routing information and MSD capability advertisements simultaneously. This universal approach allows a single protocol to handle multiple functions (routing + capability exchange), eliminating the need for separate specialized protocols and reducing overall system complexity.
2Measurement precision
If PCEP protocol is used for MSD advertisement, then controllers can obtain accurate network element capabilities, but path computation speed decreases due to additional protocol overhead
Solution Approach 1:
The patent combines MSD capability advertisement with existing IS-IS routing update messages, merging two functions (capability exchange and routing information propagation) into a single protocol mechanism. This eliminates the need for separate PCEP communication overhead, thereby maintaining accurate capability information while improving path computation speed.
3Productivity
If maximum SID depth is not properly communicated, then network elements cannot be fully utilized, but network congestion and failures increase due to inadequate path planning
Solution Approach 1:
The patent implements preliminary advertisement of MSD values through IS-IS routing updates before path computation occurs. By pre-publishing capability information in the routing infrastructure, controllers can proactively plan paths that respect network element limitations, thereby fully utilizing available capacity while preventing network failures through advance awareness of constraints.
Data Source
AI summary
Techniques for exposing maximum node and/or link segment identifier depth using IS-IS are described. A network element in a Segment Routing (SR) network transmits a Type Length Value (TLV) element including a Maximum Segment Identifier Depth (MSD) value. The MSD value identifies a maximum number of segment identifier (SID) labels that the network element is able to push into packet headers of received packets to enable forwarding of the received packets through the SR network. The network element receives, from a controller, data for a path to be utilized by the network element for forwarding the received packets through the SR network. The data includes one or more SID labels to be pushed into the received packets, and the SID labels include fewer than or equal to the MSD value. The controller and the network element do not utilize the Path Computation Element Protocol (PCEP) over a southbound interface.