How does NSP enable path control?

Path control for NSP

NSP provides a view of the IGP topology and PCE LSPs. It also displays the status of the IGP network and provides functionality to optimize the network resources.

NSP leverages centralized, intelligent network control capabilities so that operators can rapidly adapt to changing demand and traffic patterns and run their networks more efficiently. It accepts path connection requests from service management operations, from OSS and orchestration systems, and from physical/virtual network elements, then calculates optimal paths through the network for a given set of business and technical constraints by leveraging centralized views of all available assets/topologies and their current state.

NSP's path control functions are based on a Path Computation Element (PCE) architecture that integrates standard protocols such as PCEP to open up path computation to external control. This allows PCCs to be enhanced with various path optimization algorithms that ensure optimal path placement across the network. NSP's path control implementation is stateful in nature and will maintain an up-to-date Traffic Engineering Database (TED), as well as the current RSVP-based label switched paths (LSP) and the segment routing path (SRP) state. It tracks RSVP BW and manages BW for the Segment-Routed TE paths as a unified state.

Multi-domain path computation

NSP supports path computation across multiple IGP instances. These instances are discovered as admin domains with stitching points on the common ASBR routers. The path traversal algorithm uses a flat graph and computes the shortest path based on the required metric. NSP PCE precomputes inter-domain path reachability, pruning domains in order to avoid visiting domains which may form loops or which don’t reach the destination. All existing constraints apply, such as diversity and Max SID Depth. Both Segment-Routed TE paths and RSVP TE paths are supported and deployed.

Northbound interface for topology retrieval

NSP supports both an IETF-based NBI and a proprietary NBI model with extended attributes for topology retrieval. This is in addition to the existing IETF-based NBI. Using this NBI, northbound applications can obtain the IP and TE topology from NSP, including additional information (such as area number/level instance and node/link/prefix SIDs). Northbound applications and controllers, such as NSP's own IP/Optical coordination, can also modify the following TE attributes: SRLG, TE metric, IGP metric, Latency, and admin group.

Unnumbered interface support

NSP allows an LSP to be computed over a set of links where the interfaces are unnumbered. After configuring unnumbered interfaces and OSPF/ISIS link interfaces with TE enabled, the link appears in the path control network map. Only TE-enabled OSPF/ISIS unnumbered interfaces are supported. If TE is later disabled, the links become operationally down.

If the BGP-LS message contains "local if index" and "remote if index", paring between incoming and outgoing links will be allowed. As a result, the two links will be shown as one on the network map. If the BGP-LS message only contains “local if index”, paring is not possible. The LSP pathfinder algorithm is able to find and use unnumbered interfaces in the same manner as regular interfaces.

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