Subject: Re: [mpls-tp] [PWE3] Pseudo-wires: uni-directional o bi-directional?

From: venkatesan mahalingam <[email-masked]>
Date: Tue, 29 Jun 2010 00:54:59 +0530

Hi Sasha and all,

>> I tend to agree with your interpretation: “co-routed” means “co-routed in
the immediate lower layer”, and hence PWs (both single-segment and
multi-segment) are co-routed bi-directional LSPs.

Can we always agree that “co-routed” means “co-routed in the immediate lower
layer”?

I really don't understand the point that both SS-PW and MS-PW are co-routed
bidirectional LSPs.

I think, PWs use the LSPs as the transport medium to send its packet to one
PW endpoint and another PW end point. so, LSPs' (server layer - section)
co-routed/associated bi-directionality will be applicable for client layer
(PWs) also.

But for LSPs run over datalink, I think, we don't consider the data link's
co-routed/associated bi-directionality for LSPs as datalink is used between
nodes.

Can you guys please make the things clear for PWs on layer network?

-- 
Best Regards,
Venkatesan Mahalingam.

*From:* [email-masked] [mailto:[email-masked]] *On
Behalf Of *Greg Mirsky
*Sent:* Monday, June 28, 2010 10:21 PM
*To:* [email-masked]
*Cc:* pwe3; MPLS TP
*Subject:* Re: [mpls-tp] [PWE3] Pseudo-wires: uni-directional o
bi-directional?

Dear Stewart,
perhaps I'm applying section/segment terminology to PW without sufficient
explanation of my view. After reading comments by you and Sasha I've looked
at SS-PW as a bi-directional link or section. If such presentation of SS-PW
is valid then it's co-routedness, as you've noted, is obvious. I agree that
SS-PW can be referred as segment as well but then its co-routedness is not
self-evident. Interestingly, from the view of SS-PW as a bi-directional
link/section directly follows bi-directional co-routed essence of MS-PW.

Regards,
Greg

On Mon, Jun 28, 2010 at 12:26 PM, Stewart Bryant
<[email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3astbryant%40cisco.com>>
wrote:

Greg

I do not understand your point.

MS-PW S-PEs serve a purpose in breaking the PW into segments. If you do not
need that decomposition in a network, there is nothing requiring their use.
However we should not prohibit their use either, as there are scenarios
whether this decomposition is of benefit.

If you need an existence proof of this point, remember that we initially
designed SS-PW and needed to create MS-PW to address requirements of network
operators that has deployed SS-PW.

Stewart

On 28/06/2010 15:01, Greg Mirsky wrote:

Dear Sasha,
I too find Stewart's explanation very useful for overall MPLS-TP. And in
this perspective perhaps the SS PW might be also referred as PW section.

Regards,
Greg

On Mon, Jun 28, 2010 at 8:56 AM, Alexander Vainshtein <
[email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3aAlexander.Vainshtein%40ecitele.com>>
wrote:

Stewart,

Lots of thanks for a prompt and unambiguous response..

This issues looks like one more fine point of MPLS-TP-ese to me: Does
“co-routed” mean “co-routed in the immediate lower layer” or “co-routed in
all the underlying layers down to the duct”?

FWIW, I tend to agree with your interpretation: “co-routed” means “co-routed
in the immediate lower layer”, and hence PWs (both single-segment and
multi-segment) are co-routed bi-directional LSPs.

Regards,

     Sasha

*From:* [email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3apwe3-bounces%40ietf.org>[mailto:
[email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3apwe3-bounces%40ietf.org>]
*On Behalf Of *Stewart Bryant
*Sent:* Monday, June 28, 2010 3:46 PM
*To:* [email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3apwe3%40ietf.org>

*Subject:* Re: [PWE3] Pseudo-wires: uni-directional o bi-directional?

It seems to me that PWs are associated bi-directional LSPs...

PWs are co-routed bi-directional since it is required that they go through
the same xPEs in each direction, and the xPEs knows about the association of
the two directional components.

Whether they run over co-routed bi-directional, or associated bi-directional
LSP is a deployment/applicability issue.

- Stewart

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---

From: Greg Mirsky <[email-masked]>
Date: Mon, 28 Jun 2010 12:37:00 -0700

Dear Venkatesh,
you've said "I really don't understand the point that both SS-PW and MS-PW
are co-routed bidirectional LSPs."
I think that all MPLS-TP documents properly distinguish between PW and LSP.
The co-routedness of the PW is in regard to the fact that all of its end and
transit points (T-PEs and S-PEs) must be aware of relationship between
forward and backward/reverse directions. The co-routed nature of a PW in no
way determines or requires type of tunnel it is mapped to. For example, the
tunnel could be associated bi-directional LSP the PW still will be viewed as
having a co-routed path.

Regards,
Greg

On Mon, Jun 28, 2010 at 12:24 PM, venkatesan mahalingam <
[email-masked]> wrote:

> Hi Sasha and all,
>
> >> I tend to agree with your interpretation: “co-routed” means “co-routed
> Can we always agree that “co-routed” means “co-routed in the immediate
> lower layer”?
>
> On Mon, Jun 28, 2010 at 12:26 PM, Stewart Bryant <[email-masked]<https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=mailto%3astbryant%40cisco.com>>
> wrote:
>
> Greg
>
> FWIW, I tend to agree with your interpretation: “co-routed” means
> “co-routed in the immediate lower layer”, and hence PWs (both single-segment
> and multi-segment) are co-routed bi-directional LSPs.
>
>
>
> Regards,
>
>      Sasha
>
>
>
> Whether they run over co-routed bi-directional, or associated
> bi-directional LSP is a deployment/applicability issue.
>
> - Stewart
>
>
>
> http://www.cisco.com/web/about/doing_business/legal/cri/index.html <https://inowa.aricent.com/owa/redir.aspx?C=af2c518a1d214b41962d6a2e2ec260e5&URL=http%3a%2f%2fwww.cisco.com%2fweb%2fabout%2fdoing_business%2flegal%2fcri%2findex.html>
>
>
>
>