The MPLS WG Archive

[Chopin He <chopin.he@bigfoot.com>]

Hi! folks!

I hope this is the right place to ask this stupid MPLS question.

I read couple of I-Ds mentioning "Path Computation Server", But I am a 
bit unclear about its definition and functionality.

So far, PCS is mentioned in many documents [1][2][3][4][5], one example 
of its definition is found as:[1]

   "PCS: Path Computation Server (may be any kind of LSR (ABR, ASBR, ...)
    or a centralized path computation server "

This is quite a detailed explaination, but I understand the LSR or ABR 
or ASBR are control plane components; while the centralised path 
computaton server is a management plane component. In some case, (e.g. 
network management), their roles are lardgely different. Is that 
possible to define them seperately?


Additionaly, it seems to me that PCS's functionality is to response the 
PCC's Path Computation Request, thus compute the path, and send the 
result back to PCC. This sounds perfect. While I am still a bit unclear. 
  What kind of information the PCS need to know? How can the PCS get the 
relevant information? And so on.

E.g. Brunner said in [3]:
    "Definitely the path computation server needs topology information in
    order to perform its task. But how to get that information is out of
    scope of this document. "

I wonder if there are some specification which defines the PCS's 
functionality explicitly?

If not, can somebody take the initiative?



Thanks for your time to read this mail.



Best wishes!


--
Chopin



[1] Vasseur JP, et al., “RSVP Path computation request and reply 
messages”, <draft-vasseur-mpls-computation-rsvp-03.txt>, IETF work in 
progress, Jun 2002.

[2] JP Vasseur, "IS-IS Path Computation Server discovery TLV", 
<draft-vasseur-mpls-isis-pcsd-discovery-01.txt>, IETF work in progress, 
June, 2002

[3] M. Brunner, " COPS usage for Path Computation Servers (COPS-PCS)", 
<draft-brunner-mpls-cops-pcs-00.txt>, IETF work in progress, September, 2002

[4] JP Vasseur, Peter Psenak, "OSPF Path Computation Server discovery", 
<draft-vasseur-mpls-ospf-pcsd-discovery-00.txt>, IETF work in progress, 
June, 2002

[5] JP Vasseur, Peter Psenak, "OSPF Traffic Engineering capability TLVs 
", <draft-vasseur-mpls-ospf-te-cap-00.txt>, IETF work in progress, 
October, 2002