Subject: Re: [mpls-tp] Results of informal review of Section 3.4 draft-ietf-mpls-tp-framework-07

From: Stewart Bryant <[email-masked]>
Date: Mon, 01 Feb 2010 12:13:54 +0000

Rahul
> In other words why is it not necessary and
> sufficient to restrict the server layer to MPLS-TP LSPs?
>   
The client may not be a network layer protocol (RFC5654 Req 30) and the 
standard IETF protocol for carrying L1 and L2 protocols over an LSP is a PW.

Therefore the server layer presentation to the client needs to be a PW 
in some cases, and in such cases, the the PW needs to support the same 
grade of OAM as the LSP layer.

- Stewart

---

From: <[email-masked]>
Date: Mon, 1 Feb 2010 13:03:37 -0000

Stewart wrote 01 February 2010 12:14

> To: Rahul Aggarwal
> Cc: Harrison,N,Neil,DKQ7 R; [email-masked]; 
> [email-masked]; [email-masked]
> Subject: Re: [mpls-tp] Results of informal review of Section 
> 3.4 draft-ietf-mpls-tp-framework-07
> 
> Rahul
> > In other words why is it not necessary and sufficient to 
> restrict the 
> > server layer to MPLS-TP LSPs?
> >   
> The client may not be a network layer protocol (RFC5654 Req 
> 30) and the standard IETF protocol for carrying L1 and L2 
> protocols over an LSP is a PW.
> 
> Therefore the server layer presentation to the client needs 
> to be a PW in some cases, and in such cases, the the PW needs 
> to support the same grade of OAM as the LSP layer.
> 
> - Stewart
> 
As we discussed on the MPLS-TP call last Tues, the term 'network layer',
as originally implied in the OSI L3 case, is just plain technically
wrong.  We only use it, and the equally misleading L1 and L2 terms,
because they are steeped in historical use.  But since we are wiser now
(or at least we should be) we should try and stop promulgating these
technically incorrect terms in future standards work.

We should also not hold PWs in any great esteem IMO, as they are only an
artefact of the specific arch flaws in LDP...if we remove LDP, as we
must in MPLS-TP, then the conditions that created PWs are also removed.

The only technical reason I got from last Tuesday's call for PWs to
carry on in MPLS-TP is because they have T-LDP signalling and this is
considered useful (vs RSVP-TE signalling for the MPLS-TP LSPs).  The DP
CW is not useful IMO in MPLS-TP, as the majority of it is simply
redundant in MPLS-TP.

So it for sure looks like we are imposing artificial and IMO technically
incorrect conditions on MPLS-TP.

Aside=> The major service one wants from a server layer (in a
client/server sense) is transparency.  I'm not going to go into the
details here, but transparency demands certain behaviours of the server
layer.  Further, if one want performance isolation between different
clients, such that the traffic behaviour of client X cannot impact the
SLA enjoyed by client Y, the server layer must (i) use proper single
source connections (necessary requirement) and (ii) not overbook its
resources (full sufficiency requirement).  The co-cs mode always
satisfies these requirement, the co-ps mode must be consciously
engineered to do so.

regards, Neil