Segment Routing Bandwidth Reservation via Centralized PCE
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Solution Overview
Problem
Segment Routing introduces challenges in bandwidth reservation and diverse path services due to its ability to diverge from intended paths, especially under link failures and repairs, requiring real-time topology management and optimization to maintain service level agreements (SLAs).
Innovation Solution
A centralized Path Computation Element (PCE) allocates bandwidth using Segment Routing, tracks network changes, and computes new paths and Segment Identifier (SID) lists to ensure the service path remains valid and optimized, signaling intended paths and using expanded SID lists to validate candidate paths, ensuring traffic adheres to user-defined constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If Segment Routing uses compressed SID list for path representation, then path provisioning is simplified and scalability is improved, but the current path may diverge from the intended path causing bandwidth reservation failures
Solution Approach 1:
The patent introduces a Path Computation Element (PCE) as an intermediary that receives service requests, computes intended paths, and generates corresponding SID lists. The PCE acts as a mediator between the service provider's intent and the Segment Routing network's actual path selection, ensuring that the computed path and generated SID list are aligned to prevent divergence and maintain bandwidth reservation reliability.
Solution Approach 2:
The patent implements a feedback mechanism where the PCE monitors network topology changes and service path status. When topology changes occur or when path divergence is detected, the PCE receives feedback about the current state and recomputes appropriate SID lists to restore alignment between intended and actual paths, thereby maintaining bandwidth reservation integrity.
2Speed
If the network uses on-router computation of shortest paths in Segment Routing, then routing autonomy and speed are improved, but the service path may deviate from the intended path after link failures or repairs
Solution Approach 1:
The patent applies preliminary action by having the PCE pre-compute the intended path and generate the corresponding SID list before traffic is actually sent. The SID list is provisioned in advance with the understanding that it encodes the intended path. This preliminary provisioning allows the network to quickly follow the pre-determined path without needing to recompute during traffic flow, while still maintaining the ability to react to failures.
Solution Approach 2:
The PCE serves as an intermediary that translates service provider path intent into Segment Routing's compressed SID list format. This translation ensures that the autonomous on-router path computation in Segment Routing aligns with the intended service path, even after network changes. The PCE mediates between the high-speed autonomous routing and the need for path consistency.
3Reliability
If a PCE signals a new SID list when path divergence occurs, then path correctness is restored, but the response time takes tens of seconds which is too slow for real-time requirements
Solution Approach 1:
The patent implements continuity of useful action by having the PCE continuously monitor network topology changes and maintain an up-to-date understanding of the network state. Instead of waiting for path divergence to occur and then reacting, the PCE continuously updates its knowledge of topology changes and can proactively adjust SID lists or quickly react to failures, reducing the time lag and maintaining continuous path correctness.
Solution Approach 2:
The PCE performs preliminary computations and preparations by pre-computing alternative paths and having ready-to-use SID lists for different network states. When a failure or topology change occurs, the PCE can quickly switch to pre-computed solutions rather than performing full path recomputation from scratch, significantly reducing the response time while maintaining path correctness.
4Reliability
If the service provider reserves bandwidth on the intended path, then SLA guarantees are maintained, but future requests may be blocked when the intended path is no longer optimal
Solution Approach 1:
The patent applies dynamics by making bandwidth reservations adaptive rather than static. The PCE continuously monitors network conditions and can dynamically adjust or release bandwidth reservations based on current network state and service requirements. This allows the system to maintain SLA guarantees when needed while freeing up capacity for future requests when the original intended path is no longer optimal, providing both reliability and adaptability.
Data Source
AI summary
Systems and methods include receiving a request for a service in a Segment Routing network; determining an intended path for the service, provisioning a head-end node with a Segment Identifier (SID) list for the intended path, and reserving bandwidth for the service on the intended path; monitoring the Segment Routing network; and responsive to a condition determined based on the monitoring, updating the SID list for the service. The condition can include a current path for the service in the Segment Routing network differing from a provisioned path in the Segment Routing network. The condition can be based on any of a failure in the Segment Routing network, a topology change in the Segment Routing network, bandwidth changes in the Segment Routing network, an optimization timer, and input from an operator.