Pre-calculated Loop-Free Alternate Next Hops for Fast Convergence
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Solution Overview
Problem
Conventional link state routing protocols, such as OSPF and IS-IS, experience significant delays in adapting forwarding tables to network topology changes due to link or router failures, leading to prolonged convergence times that negatively impact sensitive applications like VoIP and multimedia, which require end-to-end failure detection and recovery within 50 milliseconds.
Innovation Solution
The implementation of a method to pre-calculate loop-free alternate next hops using a fast algorithm that requires only two Shortest Path First (SPF) computations, allowing for immediate switching to an alternate next hop when a primary next hop becomes unavailable, thereby reducing packet loss during router convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional link state routing protocols are used to adapt forwarding tables after link failure, then routing correctness is maintained, but convergence time increases to 500 milliseconds or several seconds
Solution Approach 1:
The patent pre-calculates loop-free alternate next hops before link failures occur and installs them in the forwarding table alongside primary next hops. When a link failure occurs, the router can immediately switch to the pre-calculated alternate next hop without waiting for the shortest path algorithm to re-compute routes, thus achieving fast convergence while maintaining routing correctness.
2Reliability
If the shortest path algorithm is re-computed after every link failure to ensure optimal routing, then routing optimality is maintained, but computation time and processing overhead increase significantly
Solution Approach 1:
The patent performs preliminary computation of loop-free alternate next hops using the shortest path algorithm before failures occur. These pre-computed alternates are stored in the forwarding table. When failures occur, the router simply switches to pre-computed alternates without re-running the full shortest path algorithm, thus maintaining routing optimality while significantly reducing computation time.
Solution Approach 2:
Instead of re-computing the full shortest path algorithm for all routes after every failure, the patent computes only the necessary alternate next hops for affected destinations. This partial computation approach maintains routing optimality for critical paths while reducing overall computation overhead.
3Loss of time
If alternate next hops are pre-calculated and installed in the forwarding engine, then failure recovery time is reduced to under 50 milliseconds, but the complexity of the routing protocol increases
Solution Approach 1:
The patent extends the existing shortest path computation to pre-calculate and install alternate next hops in the forwarding table before failures occur. This approach leverages the existing routing protocol infrastructure and adds minimal complexity while achieving fast failure recovery under 50 milliseconds.
Solution Approach 2:
The patent makes the forwarding table multi-functional by storing both primary next hops for normal operation and alternate next hops for failure scenarios in the same data structure. This universal approach simplifies the system architecture compared to maintaining separate routing mechanisms, thus reducing overall complexity while enabling fast recovery.
4Measurement precision
If comprehensive SPF computations are performed to compute optimal distances from all neighboring devices, then accuracy of alternate next hop selection is improved, but the number of computations increases with the number of neighbors
Solution Approach 1:
The patent computes optimal distances only for neighboring devices that are relevant candidates for alternate next hops, rather than performing comprehensive SPF computations for all neighbors. This partial computation approach maintains sufficient accuracy for selecting valid loop-free alternates while reducing the number of SPF computations independent of the total number of neighbors.
Data Source
AI summary
A network device includes a route selection module configured to select an alternate next hop to use in forwarding network traffic to a destination in the event a primary next hop becomes unavailable, wherein a path to the destination device associated with the alternate next hop does not send packets through the network device. The route selection module computes optimal distances from neighboring devices to the network device, wherein a number of Shortest Path First (SPF) computations required for computing the optimal distances is independent of the number of neighboring devices in the network, identifies as candidate alternate next hops those neighboring devices having distances to the destination that are less than the sum of the optimal distance from the neighboring device to the network device and the optimal distance from the network device to the destination, and selects the alternate next hop from among the stored candidates.