Re: [OSPF] Comments on draft-ietf-ospf-te-link-attr-reuse-01.txt and draft-ietf-isis-te-app-01.txt

[<[e-mail]>]

Hi Acee,

I agree, but I'm not referring to Unidirectional residual, available and utilized bandwidth as per RFC 7471.

My comment concerns the MaximumBandwidth, MaximumReservableBandwidth and UnreservedBandwidth parameters defined in RFC 3630that are used by the CSPF to compute the path. These one are not aggregate if I correctly understand the proposed draft. I also don't understand why these standard TE parameters are duplicate in the ISIS draft and not mention in the OSPF draft. Do we go to a different behaviour between IS-IS and OSPF ?

Now, if the proposed drafts aims to used onlythese new Performance Metrics without duplicate them per application, my question becomes: Why a new drafts ? Why not simply implement RFC 7471 and RFC 7810 ? Up to now, I know only one partial implementation of these 2 RFCs (in FR-Routing Open Source project).

Regards

Olivier


Le 25/10/2017 à 01:25, Acee Lindem (acee) a écrit :
> Hi Olivier, 
>
> If you read the definitions of Unidirectional residual, available, and
> utilized bandwidth in RFC 7471 you will note that these are all aggregate
> rather than application specific values. In other words, they will not
> vary per application.
>
> Thanks,
> Acee 
>
> On 10/16/17, 11:03 AM, "OSPF on behalf of [e-mail]"
> <[e-mail] on behalf of [e-mail]> wrote:
>
>> Dear authors,
>>
>> Please find below a comment on both
>> draft-ietf-ospf-te-link-attr-reuse-01.txt and
>> draft-ietf-isis-te-app-01.txt.
>>
>> I consider the use case of bandwidth reservation. I know this is not the
>> most common use case, but the one I known well. The context is that of an
>> operator who would setup some RSVP-TE tunnels and simultaneously SR-TE
>> paths with bandwidth reservation. In this particular case, it is not
>> possible to manage both reservation with the drafts as they are.
>>
>> Indeed, in OSPF draft, it is not proposed to advertised the usual
>> bandwidth parameters as defined in RFC3630 and in ISIS, it is proposed to
>> duplicate these parameters per application. The main problem arises from
>> the fact that each application, in this case SR-TE and RSVP-TE,
>> independently compute a path and therefore reserve bandwidth on their
>> respective set of parameters. However, this will lead at a some point to
>> bandwidth overbooking, which exactly what an operator wants to avoid by
>> performing bandwidth reservation. Even if a PCE can be used to handle
>> both the RSVP-TE tunnels and SR-TE paths, the same problem arises because
>> each path computation is performed on a different set of bandwidth
>> parameters i.e. one TED per application whereas these information relate
>> to the same links. Of course a central entity like a PCE might try to
>> reconcile the information into a single TED, but this will greatly
>> increase the complexity of the PCE with a risk that the TE information
>> will
>> never be up to date, so at the end unnecessary.
>>
>> So, for me there are only 2 possibles solutions to avoid this overbooking
>> problem:
>>
>> 1/ Split and partition network resources to avoid conflicts. But, this
>> leads into a poor network usage. Indeed, if an application like RSVP-TE
>> uses less bandwidth than its budget, why the SR-TE application could not
>> reuse them if it has reached its threshold ? The under utilization of
>> network resources will increase proportionally with the number of
>> applications. Imagine if we want to use this principle for network
>> Slicing. I understand the advantage for vendors, but I'm on the operator
>> side ;-)
>>
>> 2/ Each time an application reserved some bandwidth, the routers
>> concerned by this new path must update the bandwidth parameters of the
>> concerned link not only to the given application, but also to all others.
>> For example, when RSVP-TE setup a tunnel, Unreserved Bandwidth parameters
>> must be updated in the standard RFC3630 set, but also in SR-TE parameters
>> set. But, in this case, why duplicate TE parameters if at the end all set
>> carry the same values, apart wasting CPU and bandwidth ?
>>
>> In summary, duplicate TE information is only relevant for the added
>> metrics i.e. delay, loss, jitter ... but unusable for concave metrics
>> i.e. bandwidth.
>>
>> Can you explain me how you intend to solve this issue as both possible
>> solutions are not suitable for an operator.
>>
>> Best Regards
>>
>> Olivier
>>
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