Path Computing and Signaling

A path in a segment routing domain consists of a list of SIDs that identify the path from the source to the destination. A Path Computation Element (PCE) assists network nodes, known as Path Computation Clients (PCCs), by computing paths based on network topology information acquired from the IGP (IS-IS) and path computation constraints like the IGP metric. The path computation can be triggered by the PCE or the PCC, which are then correspondingly called PCE-initiated and PCC-initiated paths.

In this test, two types of paths were computed, which are segment routing policy (SR-Policy) as defined in the draft "draft-ietf-pce-segment-routing-policy-cp" and segment routing traffic engineering (SR-TE) as defined in the "RFC8664". The test iterations also involved multiple scenarios, like using SR-MPLS and SRv6 (full SID and μSID) as the dataplane. Besides using PCEP for the path request and signaling, BGP was also utilized in some iterations to signal PCE-initiated paths to the PCC. 

The steps used to conduct the test were as follows

• Verify the PCEP status between the PCE and the PCC
• (PCEP) Trigger a path computation either by the PCC or the PCE
• (PCEP) Verify that the PCC reported the path instantiation to the PCE
• (BGP) Compute and signal a path from PCE to the PCC
• Verify the correct path instantiation on the PCC