Subject: "Path Computation Server" Definition and Functionality Description

From: Chopin He <[email-masked]>
Date: Mon, 25 Nov 2002 19:38:15 +0200

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

---

From: Jean Philippe Vasseur <[email-masked]>
Date: Mon, 25 Nov 2002 15:08:09 -0700

Hi,

At 19:38 25/11/2002 +0200, Chopin He wrote:
>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]
>
>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?
>
>
>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.
>

The PCS's role is to compute TE LSP path for which it is not the HE.
Basically, the PCS needs:
- to get information about the topology, the TE resources, .... This can be 
done in several ways: downloading those informations from a router using a 
Telnet session, having a routing adjacency with a router, ...
- some algorithm(s) to perform TE LSP path computation,
- to provide the computed TE LSP path to the PCC (routers) using Telnet, a 
signalling protocol (Ex: [1])
Example 1: PCS= a UNIX station being able to receive request from routers 
to compute TE LSP path for primary TE LSP placement, inter-area TE LSPs, 
non packet TE LSP paths, bypass tunnel path computation, ...
Example 2: PCS= an ABR (scenario 2 or 4 of draft 
http://www.ietf.org/internet-drafts/draft-kompella-mpls-multiarea-te-03.txt)) 
for inter-area TE LSP path computation,
Example 3: any router is a PCS to compute the bypass tunnel(s) path for 
each of its neighbors to their respective (N)NHOP(s) LSRs. See the 
distributed bypass tunnel path computation scenario of 
http://www.ietf.org/internet-drafts/draft-vasseur-mpls-backup-computation-01.txt

JP.

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

---

From: Marcus Brunner <[email-masked]>
Date: Wed, 27 Nov 2002 12:31:16 +0100

As Jean Philippe has meantioned there are a number of ways how to get the 
required information to a central place, therefore is is pretty 
solution/implementation specific and therefore should not be standardized.

The information you need heavily depends on the algorithm you want to run 
in the PCS. The algorithm on the other hand might depend on the type of 
service request (currently this naturally out-of-scope of the WG)

Marcus

--On Montag, 25. November 2002 15:08 -0700 Jean Philippe Vasseur 
<[email-masked]> wrote:

>> 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.
>>
> - to get information about the topology, the TE resources, .... This can
> be done in several ways: downloading those informations from a router
> using a Telnet session, having a routing adjacency with a router, ... -
> some algorithm(s) to perform TE LSP path computation,
> - to provide the computed TE LSP path to the PCC (routers) using Telnet,
> a signalling protocol (Ex: [1]) Example 1: PCS= a UNIX station being able
> to receive request from routers to compute TE LSP path for primary TE LSP
> placement, inter-area TE LSPs, non packet TE LSP paths, bypass tunnel
> path computation, ... Example 2: PCS= an ABR (scenario 2 or 4 of draft
> http://www.ietf.org/internet-drafts/draft-kompella-mpls-multiarea-te-03.t
> xt)) for inter-area TE LSP path computation, Example 3: any router is a
> PCS to compute the bypass tunnel(s) path for each of its neighbors to
> their respective (N)NHOP(s) LSRs. See the distributed bypass tunnel path
> computation scenario of

--------------------------------------
Dr. Marcus Brunner
Network Laboratories
NEC Europe Ltd.

E-Mail: [email-masked]
WWW:    http://www.ccrle.nec.de/
Phone: +49 (0) 6221 905 11 29
personal home page: http://www.brubers.org/marcus