Subject: RE: [PWE3] Segmented PWs

From: [email-masked]
Date: Tue, 12 Jul 2005 18:06:31 +0100

Scott,

See in-line.

Ben

> -----Original Message-----
> From: Scott W Brim [mailto:[email-masked]] 
> On 07/08/2005 10:45 AM, [email-masked] allegedly wrote:
> > "In a client/server relationship the performance of the 
> client layer 
> > is equal to the performance of the server layer plus any 
> impairments 
> > introduced by the client layer itself.  Therefore it is not 
> possible 
> > for the client layer to provide better performance than the server 
> > layer over which it is transported.
> 
> Ben, as I think we discussed somewhere, "performance" is a 
> service issue, and ultimately the only measurement that 
> matters is at the application.  That is, some of the 
> performance characteristics which one might treasure in a low 
> level transport technology might be irrelevant to the 
> services you are actually trying to deliver over the higher 
> layer.  If you want to put text like this in, let's be clear 
> on what it's important to measure.  It depends on the 
> particular performance metric(s) you care about in the client 
> layer network.  As Stewart points out, some of those 
> performance metrics are better met in a PW environment.  Does 
> that fit with your premise?

Two things.  I tend to agree that ultimately performance only matters at
the 'service', however what if the 'service' is a transport (stratum)
service e.g. a network builder type service.  For example if Operator X
sells an ATM link connection to Operator Y, but Operator X provides that
ATM link connection using a ATM PW?  Then the performance
characteristics which one might treasure in a low level transport
technology may be relevant to the service?  So I think we may agree
(basically that it depends on the particular performance metric(s) you
care about in the client layer network).  The intention of my proposed
text is not to be prescriptive but just to offer guidance that this
issue of perfance inheritance should be carefully considered before
peering two server layers with each.

Re: Stewart's point about some performance metrics may be better met in
a PW environment.  I agree this may be the case and needs to be
considered as part of the 'careful consideration' I mention above. So I
think what your saying is X over Y over Z may not be suitable for
supporting application/service X but X over Y-PW over Z maybe suitable,
in which case I agree as I believe the performance inheritance needs to
be considered on an individual basis.

> > Note: Due to this vertical performance inheritance and the 
> different 
> > performance provided by, and the characteristics of, each 
> networking 
> > mode it is generally advisable to stack modes that less efficiently 
> > provide dedicated bandwidth/performance on top of modes that more 
> > efficiently provide dedicated bandwidth/performance.
> 
> Not directly deducible from previous text.  Is the ability to 
> provide dedicated bandwidth the only interesting metric?

Most probably not, but I only provided the text as a 'starter for 10' to
generate some debate etc.  I'm not a expert on performance.

> > Therefore, it is necessary to carefully consider which server layer 
> > modes (and/or technologies) it is appropriate to peer with 
> one another 
> > in order to provide the topmost client layer (the 
> 'service') with the 
> > performance that it requires.  This is a horizontal performance 
> > relationship because the server layer partitions are peered 
> with each 
> > other horizontally."
> 
> This I like :-)

Good, this is my main point, i.e. this performance inheritance needs to
be considered & thought about at some point, preferably prior to
deploymment :-)

Ben

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---

From: Scott W Brim <[email-masked]>
Date: Tue, 12 Jul 2005 13:17:48 -0400

Yes.  OK.  See you there.

---

From: Luca Martini <[email-masked]>
Date: Mon, 25 Jul 2005 08:06:01 -0600

Ben,

Yes, I think that including this text is a good idea. The performance of 
the PW  ( client ) can only be as good as the performance offered by the 
transport ( Server ).
I will format this text for terminology , and include a form of it in 
the next version.

Luca