Subject: Re: draft-ietf-tewg-diff-te-reqts-01.txt

From: Francois Le Faucheur <[email-masked]>
Date: Thu, 21 Jun 2001 16:31:50 +0200

Darek,

taking this discussion onto the TEWG list:

At 15:12 19/06/2001 -0400, Darek Skalecki wrote:
>Hi,
>
>The requirements draft is really well written. I have however a concern 
>with respect to preemption between/within class-types (Section 2.5). 
>Basically, what governs whether preemptee should be chosen from our 
>class-type or another class-type.
>
>To illustrate my point, the following example is taken from the document 
>but is extended with priorities.
>>
>>
>>    As an example, let's consider the case described in section 2.2
>>    where the following bandwidth constraints are configured:
>>    - DS-TE never routes more than say 70% of EF on a given link
>>    - DS-TE never routes more than 100% of EF+BE on that link.
>>
>>    Let's assume that DS-TE has actually established at a given time:
>>    - 50% worth of EF TE-LSPs and
>Assume 30% is at priority 0 and 20% at priority 8
>>
>>    - 50% worth of BE TE-LSPs.
>Assume all 50% is at priority 2.
>>
>>    Let's also assume that a new EF TE-LSP worth 10% now needs to be
>>    established and contends for this link.
>Assume this new EF TE-LSP wants resources at priority 1. Question now 
>becomes: should this new EF TE-LSP preempt some of the BE TE-LSPs which 
>are all at priority 2 or should it preempt some of the EF TE-LSPs at 
>priority 8?, i.e. should it preempt from its own class-type or another 
>class-type?.

good point. this needs to be defined.

>I believe that since preemption is needed then the lowest possible 
>priority preemptee should be chosen even if it comes from our class-type.

I personally agree. Let's hear other views.

>  I believe we should state a requirement surrounding where the preemptee 
> is chosen from or else it will be open to interpretation and lead to 
> confusion.

Yes, we should cover that point in the next version.
Thanks

Francois

>Any comments/views?
>Darek
>--
>Darek Skalecki
>Nortel
>(613) 765-2252

_______________________
Francois Le Faucheur
Development Engineer, IOS Layer 3 Services
Cisco Systems
Office Phone:          +33 4 97 23 26 19
Mobile :               +33 6 89 108 159
Fax:                   +33 4 97 23 26 26
Email:                  [email-masked]
_________________________________________________________________
Cisco Systems Europe
Domaine Green Side
400, Avenue de Roumanille
Bâtiment T3
06 410   BIOT
SOPHIA ANTIPOLIS
FRANCE
_________________________________________________________________

---

From: Jim Boyle <[email-masked]>
Date: Thu, 21 Jun 2001 23:18:03 -0400

Assuming that EF is in one class type, and these particular LSPs are 
split across priorities 0 and 8 (7, more likely) and that all the BE 
ones are at priority 2 is presupposing a specific technical solution, 
which is Francois et. al.'s approach.  That is not the only technical 
approach, I've heard others discussed.

If what you are asking though is "should traffic in one class (type) be 
able to preempt traffic in another to claim resources, and should this 
be configurable as possible/impossible by operator" - good requirements 
question.  I'd reply as the others have as "yeah".  Is that not covered 
in 2.5.2?

At this time, let's try to make sure that we have covered the 
requirements in requisite, but not exhaustive detail in the draft.If 
there's something major missing, let's make that clear.

As for technical solutions, anyone who feels they have a technical 
approaches to solving the problems and detailed requirements outlined 
should be working on articulating their technical proposal.  If anyone 
has something ready for discussion, I don't see why delay in posting it. 
(currently, only francois's are documented)

After we have the requirements kicked around a bit in the WG, then I 
think it would be the right time to discussing pros/cons on difft. 
approaches.

regards.

Jim

Francois Le Faucheur wrote:

>> The requirements draft is really well written. I have however a 
>> concern with respect to preemption between/within class-types (Section 
>> 2.5). Basically, what governs whether preemptee should be chosen from 
>> our class-type or another class-type.
>> 
>> To illustrate my point, the following example is taken from the 
>> document but is extended with priorities.
>> 
>>> 
>>> 

>> becomes: should this new EF TE-LSP preempt some of the BE TE-LSPs 
>> which are all at priority 2 or should it preempt some of the EF 
>> TE-LSPs at priority 8?, i.e. should it preempt from its own class-type 
>> or another class-type?.
> 
>

---

From: Balazs Szviatovszki <[email-masked]>
Date: Fri, 29 Jun 2001 19:13:24 +0200

Jim and others,

The requirement document is very good. We think that our solution 
described in previous mails posted to TE-WG fulfils exactly 
these requirement. (See thread Re: Question to draft-lefaucheur-diff-te-ext
that was active between 11/23/00 and 11/29/00)

 > there's something major missing, let's make that clear.

We think that in order to fulfil all the points in section 2.2. 
different class-types can not have overlapping priorities. 
It would be much clearer to explicitly say this among the 
requirements. If one thinks, that overlapping priorities 
are useful, please provide an example how would you use it
in such a way that is in line with the requirements!

Example:
=======
We think the below overlapping case does not make sense:

EF -> Class-type 1 (Using priorities 1-2)
AF -> Class-type 2 (Using priorities 2-3-4)
BE -> Class-type 0 (Using priorities 5-6-7)

 > (currently, only francois's are documented)

I would describe the solution already posted to the list in a max 3 page 
draft :)))

Wrap-up of our proposal:
=======================

Four new unreserved bandwidth advertisements (one for each class-type) 
beside the already present 8 per-priority advertisements (4+8 = 12)

/Francois proposes 4x8 values to be advertised and a complicated coding scheme to reduce this. This has importance only if overlapping priorities make sense./

Balazs