Re: [CCAMP] IETF 89 Draft Agenda Posted

["VIGOUREUX, MARTIN (MARTIN)" <[e-mail]>]

Zafar,

The old age of a theory does not make it a wrong theory. Also, uses cases and existing deployments do not contradict what John points out, which is that one might not be able to find a disjoint path in a graph if it computes it after having computed a first path and pruned the selected links from the graph.

Take the example (sorry for the ugly ascii):

A----B----C
|       |        |
|____D____|

If one was to choose A-B-D-C as a path then it would be impossible to find a disjoint path afterwards.
In this graph, the only way to find disjoint paths is to look for the "shortest loop" and this must be done in one step.
Until you can demonstrate that this is false, it will remain true.

-m
________________________________
De : Zafar Ali (zali)
Envoyé : 24/02/2014 19:38
À : John E Drake; Lou Berger; Fatai Zhang; CCAMP
Cc : Alia Atlas
Objet : Re: [CCAMP] IETF 89 Draft Agenda Posted

Hi John-

Are you suggesting that an SP shall only provide disjoint service if and
only if SP know that it needs N disjoint paths ahead of time? Please bear
in mind that there are use cases when a NEW service needs to be disjoint
from an EXISTING service (without disturbing the EXISTING service).

Are you also suggesting that an implementation shall only support disjoint
service if and only if it is supporting the suurballe or similar
algorithm? If yes, may I request the mailing list how many implementations
of suurballe algorithm exists today (and deployed)? Bear in mind the paper
you cited is from 1974 and disjoint services are widely deployed.

Thanks

Regards Š Zafar


-----Original Message-----
From: "[e-mail]" <[e-mail]>
Date: Monday, February 24, 2014 11:07 AM
To: "[e-mail]" <[e-mail]>, Fatai Zhang
<[e-mail]>, "[e-mail]" <[e-mail]>
Cc: Alia Atlas <[e-mail]>
Subject: Re: [CCAMP] IETF 89 Draft Agenda Posted

>Hi (and copying Alia and Adrian),
>
>I've included Suurballe's original paper for background reading on the
>subject of computing N node disjoint paths through a network.  The
>careful reader will note that the N node disjoint paths need to be
>computed concurrently as otherwise it may not be possible to find
>disjoint paths.
>
>The implication of this is that all of the current proposals, which
>attempt to find disjoint paths sequentially are fundamentally broken.
>
>If we want to get N node disjoint paths across, I think we need to define
>a new service in which the ingress CE sends the ingress PE a request
>containing a destination (egress) CE, the number of disjoint paths N, and
>a list of its attachment circuits to be considered in the request.  What
>it receives in exchange is a list of [attachment circuit, path keys]
>which it then can include in a set of Path messages that it sends to the
>provider network.
>
>However, this is really a service-level request rather than an LSP
>establishment request and the while the latter is clearly within CCAMP's
>charter, I think the former is more in the purview of the PCE working
>group where a stateful PCE can provide this service, if it doesn't
>already.
>
>In any case, to proceed with any of the current proposals is
>irresponsible.
>
>Yours Irrespectively,
>
>John
>> -----Original Message-----
>> From: CCAMP [mailto:[e-mail]] On Behalf Of Lou Berger
>> Sent: Wednesday, February 19, 2014 7:28 AM
>> To: Fatai Zhang; CCAMP
>> Subject: Re: [CCAMP] IETF 89 Draft Agenda Posted
>>
>> Fatai,
>>       Our intent is to have the current WG draft authors propose how they
>> think the document should move forward based on the WG LC comments.
>> Given that we are not meeting until Thursday, I'd hope that WG draft
>>authors
>> take advantage of this and work/meet with the authors of the related
>>drafts to
>> come up with an approach that is inclusive of the issues and
>>alternatives
>> mentioned.
>>
>> Lou
>>
>> On 2/18/2014 10:39 PM, Fatai Zhang wrote:
>> > Hi Lou,
>> >
>> > Do you think if it is better to put presentation #4,#12,#13 close
>>(ie., treat
>> them as a group topic like diversity route)?
>> >
>> >
>> >
>> >
>> >
>> > Best Regards
>> >
>> > Fatai
>> >
>> >
>> > -----Original Message-----
>> > From: CCAMP [mailto:[e-mail]] On Behalf Of Lou Berger
>> > Sent: Tuesday, February 18, 2014 5:58 AM
>> > To: CCAMP
>> > Subject: [CCAMP] IETF 89 Draft Agenda Posted
>> >
>> >
>> > All,
>> >     The draft agenda for London was posted earlier today at:
>> > http://www.ietf.org/proceedings/89/agenda/agenda-89-ccamp
>> >
>> > Please let us (Daniele & chairs) know if you have comments or if we
>> > missed anything.
>> >
>> > Authors of WG documents,
>> >
>> > As usual:
>> >
>> > If presenting, please plan to review (present) any changes that have
>> > been recently made, any open discussions or issues, as well as planned
>> > next steps.
>> >
>> > If you are not presenting, please send this information to the WG mail
>> > list *1 week* prior to the WG meeting.
>> >
>> > Much thanks,
>> > Lou, Deborah (& Daniele)
>> >
>> > _______________________________________________
>> > CCAMP mailing list
>> > [e-mail]
>> > https://www.ietf.org/mailman/listinfo/ccamp
>> >
>> >
>> >
>> >
>>
>> _______________________________________________
>> CCAMP mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/ccamp
>>
>

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