What SROS path computation methods does NSP support?

Supported SROS path computation methods

NSP supports both Stateful and Stateless Bringup as described in draft-koldychev-pce-operational.

Nokia recommends using Stateless Bringup for interworking with SROS. This method uses the SROS CLI command “path-computation-method pce”.

The use of PCReq, followed by PCRep, enables the NSP PCE to be first to calculate paths. The NSP PCE can also consider all Path Profile and Association Group parameters - such as Diversity - when doing so.

Note that these PCReq and PCRep interactions add additional overhead. When the PCE is experiencing heavy load, PCReqs can timeout, and the subsequent retries from the PCC can exacerbate this as NSP attempts to manage the timeouts.

The use of the SROS CLI command “path-computation-method local-cspf” combined with “pce-control” is also supported, but not recommended for most deployments. In this scenario, the SROS router first calculates a path before delegating control to the PCE. Upon reception, the PCE will accept the path, if it is valid - otherwise, it calculates a new path. If the path is valid, it will be used, but may not immediately meet the Path Profile or Association Group parameters, such as Diversity. Only after the standard re-signal timer (which defaults to between 20 and 50 minutes) will all Path Profile and Association Group parameters be considered.

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