Subject: Re: [mpls] Comments on draft-weingarten-mpls-tp-ring-protection-06

From: "Weingarten, Yaacov (NSN - IL/Hod HaSharon)" <[email-masked]>
Date: Thu, 5 Jan 2012 13:06:36 +0100

Jie, Hi

Sorry for the long delay in replying to this set of comments - but it
has been a rather busy time, and I have finally been freed up a little
to address the Ring Protection document.

Please see my replies in-line below.  I will, hopefully submit an
updated version of the draft based on the resolution of your comments
(as soon as everyone is satisfied with the resolutions).

Thank you,
yaacov

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
ext Jie Dong
Sent: Friday, November 04, 2011 11:46 AM
To: [email-masked]
Subject: [mpls] Comments on draft-weingarten-mpls-tp-ring-protection-06

Hi, 

Here are some comments on this tp ring protection draft. 

1. This draft describes the label stack operation of each protection
mechanism. For better clarity, I would recommend using the same
protected LSP as example when possible, i.e. using LSR-B as the ingress
and LSR-E as the egress in all description of p2p protection, and
describes the label stack operation from the ingress to the egress.

[yw>] I will try to align the examples on p2p protection to use the
working path B-A-F in section 2.3

2. Label operation in the last paragraph before 2.3.1, "packets arrive
at LSR-B with label [LI], and then send out to LSR-A with [[PA(F)|L1]]".
Should B swap the inner label LI with LE, which is expected by the
egress LSR-F?
[yw>] On the assumption that you mean the paragraph just prior to
Section 2.3.1, you are correct and I will correct the text, thank you!

3. Label stack operation of wrapping in sec 2.3.2 needs some
clarification:

  "1. The data packet arrives at LSR-A with label stack [LI+S] (i.e. top
label from the LSP and bottom-of-stack indicator)"

If the section takes the protected LSP in figure 1 as example, LSR-A is
the ingress of SPME A-F, NOT the ingress of the ring. If the ingress LSR
is B, packets arrive at A may contain the label for SPME B-A, and the
inner LSP label LI should be swapped on LSR-B.
[yw>] To be honest, this is tied to your first question, i.e. we have
confused you by referring to a different working path, the working path
in this description is the path A-F and not B-A-F, but I will try and
align (as I mentioned above)

  "2. In the normal case (no switching), LSR-A forwards the packet with
label stack [PA1(F)|LE+S] (i.e. swap the label for the LSP, to be
acceptable to the SPME egress, and push the label for the primary SPME
from LSR-A to LSR-F)."

"LE" is defined as "the label of the LSP that is expected at the egress
point from the ring", but here it is used as the label expected by SPME
egress. Since the inner LSP label needs be swapped each time the SPME
label is popped, using "LE" for this operation may be confusing. It
would be clearer to define a new term for this.
[yw>] see my previous comment!

4. In some specifications "+S" is added to the LSP label. Does it also
allow carrying PW label or other labels in the label stack?
[yw>] This document is based on use of the Linear Protection defined in
RFC6378 which is only applicable to LSPs, so I am not sure that I
understand the full context and implications of your question.

Best regards,
Jie

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