Bidirectional Segment Routing Tunnel Identification via List SIDs
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Solution Overview
Problem
Current SR technologies in MPLS/MPLS-TP networks can only realize unidirectional tunnel identification, limiting their application in scenarios requiring bidirectional end-to-end transmission.
Innovation Solution
The implementation of bidirectional segment routing tunnels using List SIDs, which are unique labels assigned to each direction of the tunnel, allowing the tail node to identify and manage bidirectional connections by distinguishing between unidirectional tunnels through a specific label stack configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If unidirectional tunnel identification is used in SR technology, then the tunnel can be identified at the head node, but the tail node cannot identify the tunnel, limiting bidirectional transmission applications
Solution Approach 1:
The patent divides the tunnel identification mechanism into two separate directional identification mechanisms. The head node uses a first tunnel identifier to identify the tunnel in the first direction, while the tail node uses a second tunnel identifier to identify the tunnel in the second direction. This segmentation allows each node to independently identify tunnels in its respective direction, enabling bidirectional transmission applications.
Solution Approach 2:
The patent introduces a new dimension of identification by adding directional specificity to tunnel identification. Instead of a single universal identifier, the system now uses direction-aware identifiers (first tunnel identifier for head node, second tunnel identifier for tail node), allowing the tail node to identify incoming tunnels from the head node, thereby expanding adaptability to bidirectional scenarios.
2Reliability
If RSVP-TE tunnel is used, then the tunnel can be established with intermediate node state maintenance, but the scalability is poor
Solution Approach 1:
The patent extracts the state maintenance function from intermediate nodes and relocates it to the end nodes (head node and tail node). Intermediate nodes only perform label switching based on pre-configured segment lists, while the head node pushes the complete segment list and the tail node validates the incoming segments. This extraction eliminates the scalability bottleneck at intermediate nodes while maintaining connection reliability through end-to-end state management.
Solution Approach 2:
The head node and tail node perform self-service by independently managing tunnel identification and validation. The head node autonomously pushes the segment list onto packets, and the tail node autonomously validates the segment list without requiring intermediate nodes to maintain connection state. This self-service mechanism improves scalability by distributing intelligence to endpoints rather than burdening intermediate nodes.
3Device complexity
If LDP or static tunnel is used, then the control plane does not need to maintain state, but the forwarding plane requires configuration for each connection, causing scalability problems
Solution Approach 1:
The patent implements preliminary action by pre-configuring segment lists at the head node before traffic flow begins. The head node calculates the complete path segment list in advance and pushes it onto packets before transmission. This preliminary calculation and configuration at the source eliminates the need for real-time state maintenance at intermediate nodes and enables efficient service deployment without per-connection forwarding plane configuration.
Solution Approach 2:
The segment list mechanism serves multiple functions: it acts as a path specification for intermediate nodes, a tunnel identifier for the tail node, and a routing instruction for label switching. This multi-functionality eliminates the need for separate control plane state maintenance and forwarding plane configuration, improving service deployment efficiency while maintaining simplicity.
Data Source
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AI summary
Embodiments of the present disclosure provide a method and a device for implementing a bidirectional segment routing tunnel. The method includes: after receiving, by a controller, a command of establishing a bidirectional SR tunnel between a node A and a node Z, calculating, by the controller, a path between the node A and the node Z satisfying a requirement of the command, and assigning, by the controller, unique List SIDs to a tunnel in a first direction from the node A to the node Z and a tunnel in a second direction from the node Z to the node A corresponding to the path, respectively; and pushing, by the controller and at each end point of the tunnel respectively, a SR label stack on a user packet after placing the List SID, as a part of the SR label stack, into the SR label stack and forwarding the user packet.