MPLS Ring Convergence Using Dual LDP Label Tables
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Solution Overview
Problem
Conventional convergence methods in networks with ring topologies are overly complex and cannot be supported by Application-Specific Integrated Circuits (ASICs), necessitating a simplified and efficient convergence process that avoids micro-loops and supports fast convergence.
Innovation Solution
Implementing Label Distribution Protocol (LDP) to create MPLS tables for clockwise and anti-clockwise directions around a ring topology, allowing nodes to transmit packets efficiently and switch directions when links become unavailable, without relying on Ring Protection Links (RPL).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional convergence methods (PIC, LFA, RLFA, TI-LFA) are used in ring topologies, then convergence reliability is improved, but device complexity increases and ASIC support becomes unavailable
Solution Approach 1:
The patent segments the label distribution process by creating separate forwarding tables for clockwise and anti-clockwise directions around the ring. Each table contains labels specific to one direction, allowing independent optimization and simplification of each path without requiring complex interactions between multiple convergence mechanisms.
Solution Approach 2:
Instead of using complex convergence mechanisms to calculate and switch paths, the patent inverts the approach by pre-distributing labels for both directions simultaneously. When a link fails, the inversion is achieved by simply switching which label table (CW or ACW) is active, rather than recalculating paths through complex algorithms.
2Measurement precision
If conventional convergence methods are implemented, then convergence accuracy is improved, but ease of operation deteriorates due to inability to support in ASICs
Solution Approach 1:
The patent extracts the complex convergence calculation logic from the forwarding decision process. By pre-distributing labels for both directions and maintaining separate CW/ACW tables, the complex topological calculations are performed once during label distribution, while ASICs only need to perform simple table lookups based on incoming direction, making hardware implementation feasible.
Solution Approach 2:
The patent performs preliminary label distribution for both clockwise and anti-clockwise directions before any link failure occurs. Each node receives and stores labels for both directions in advance, so that when a failure happens, the ASICs can immediately switch to the appropriate pre-computed table without performing complex real-time calculations.
3Speed
If fast convergence is achieved through complex mechanisms, then convergence speed is improved, but device complexity increases making ASIC support unavailable
Solution Approach 1:
The patent implements dynamic label distribution where nodes continuously exchange labels for both CW and ACW directions with their neighbors. This dynamic pre-computation allows the system to adapt to topology changes while maintaining simple ASIC-friendly forwarding tables, achieving fast convergence through pre-established label mappings rather than complex real-time algorithms.
Data Source
AI summary
A method implemented by a node in a network utilizing Multiprotocol Label Switching (MPLS) includes performing a convergence procedure to discover the topology of a network in which multiple nodes are arranged; and upon determining that the topology of the network is a ring topology whereby the node is connected to two neighboring nodes by a respective link, creating a first table for a first link, the first table including labels representing at least a portion of a label stack for allowing the node to transmit packets to another node in the network in a clockwise (CW) direction around the ring; and creating a second table for a second link, the second table including labels representing at least a portion of a label stack for allowing the node to transmit packets to another node in the network in an anti-clockwise (ACW) direction around the ring.