Subject: MPLS Restoration

From: Irfan Lateef <[email-masked]>
Date: Wed, 03 Oct 2001 22:30:52 -0400

Hi,
   I have few doubts on MPLS restoration.
(1)The section 3.6. Fault Notification of
draft-ietf-mpls-recovery-frmwrk-03.txt says,
  " Depending on how fault notification is configured in
   the LSRs of an MPLS domain, the FIS could be sent either as a Layer 2

   or Layer 3 packet [11]. The use of a Layer 2-based notification
   requires a Layer 2 path direct to the PSL. "

  If there is an LSP from A to F as shown below and a failure has
occured
  between C & D
  A --- B --- C --- D --- E ---- F
   (a) what does it mean to have a layer 2 direct path ?

   (b) how can a direct path be setup if layer 2 is SONET or GigE?

   (c) And how do you route the FIS to the source in any layer 2
technology?

(2) I have read all the MPLS restoration drafts AFAIK, but haven't found
any
     reference to expected restoration times for path restoration or
global repair.
     My guess is it going to be in the order of seconds. Is there any
effort or work
     in progress to bring it down by an order or it is impossible and
futile effort.

Appreciate your comments.

Regards,
--
Irfan Lateef
Village Networks Inc,

---

From: "Vishal Sharma" <[email-masked]>
Date: Mon, 8 Oct 2001 11:25:17 -0700

Irfan,

Please see comments below.

>-----Original Message-----
>From: [email-masked] [mailto:[email-masked]]On Behalf Of Irfan
>Lateef
>Sent: Wednesday, October 03, 2001 7:31 PM
>To: [email-masked]
>Subject: MPLS Restoration
>
>
>Hi,

By "Layer 2" what was implied here was an MPLS LSP. The reference [11]
provided makes this clear. Perhaps we should clarify this in the text
as well.

>   (a) what does it mean to have a layer 2 direct path ?

It  means that you have an LSP in the reverse direction, from C to A
(More details are provided in [11].)

>   (b) how can a direct path be setup if layer 2 is SONET or GigE?

It cannot. Please see explanation above. (BTW, I thought SONET was
more a Layer 1 technology.)

>   (c) And how do you route the FIS to the source in any layer 2

Again, once the meaning of the term "Layer 2", as used in this
context, is clear (as explained above), one realizes that use of
"any layer 2" is not what is proposed.

>     in progress to bring it down by an order or it is impossible and

It depends on the type of restoration that is desired under global
repair.
If it is 1+1 path protection, the restoration time should
be very small (order of milliseconds), since there is no need
to signal to the source (in fact, there is no need for any signaling
at all, once the failure has been detected).
However, if more complex forms of shared
restoration are included in global repair, then the times could be
longer, since one may not only have to inform the source, one
may also have to reconfigure intermediate routers/switches/crossconnects
to realize shared restoration.

In response to your question, you might want to check out the following
two drafts:

http://search.ietf.org/internet-drafts/draft-owens-te-network-survivability-
01.txt

http://search.ietf.org/internet-drafts/draft-ietf-tewg-restore-hierarchy-00.
txt

-Vishal

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---

From: Irfan Lateef <[email-masked]>
Date: Tue, 09 Oct 2001 15:04:37 -0400

Vishal,

Thanks for the clarification about using LSP for notification.

I think chang's draft has explained it in detail. My concern is,
this idea suffers from the same scalibility issues as local repair
with detours as suggested by gan's draft. If you have N hops
you need N-1 LSPs in the reverse direction. Imagine the number
of LSPs being tunneled through a  10 gig pipe and the traffic at
the head of the pipe with RNTs when there is a failure on this pipe.

Now the tewg-restore-hierarchy draft mentions 1:1 path protection
in 100-500 ms. For the sake of argument let assume we do use RNT
and LSP. Do you think we can achieve the protection within the
timings mention above? I dont see how?

The second question is, how is the idea about reverse LSP progressing in
the working group?

Appreciate your response.

Regards,
Irfan Lateef

--
Irfan Lateef
Village Networks Inc,

---

From: Jim Boyle <[email-masked]>
Date: Tue, 9 Oct 2001 20:26:29 -0400 (EDT)

> timings mention above? I dont see how?

Or assume you don't use RNTs (as I understand them), you just send
PathErrs per LSP.... and switch traffic onto pre-signalled LSPs.  For a
network w/ a diameter on the order of 4500 km and # effected LSPs < 3-4k,
this is achievable, at least emperically.  I've even seen it work when the
head ends had to originate new connections (but, that was PNNI, which we
all know has no bearing here :)

What draft-tewg-restore-hierarchy-00 refers to in 5.2.1 as
Pre-Established is do-able.  I have doubts about Section 5.2.2 w/
Pre-planned (or shared based on SRG), but as the last paragraph says,
the first likely step is Pre-established.

regards,

Jim