Re: [mpls-tp] Proposed liaison to ITU-T on G.8110

Stewart,

could you please explain why the TTL processing in MPLS-TP is different from TTL processing in MPLS?

Alternatively, what changes in MPLS TTL processing have been defined in the last 5 years that caused the TTL processing model of G.8110 to be no longer accurate?

Thanks, Italo 

> -----Original Message-----
> From: mpls-tp-bounces@ietf.org 
> [mailto:mpls-tp-bounces@ietf.org] On Behalf Of Stewart Bryant
> Sent: lunedì 28 giugno 2010 19.42
> To: mpls-tp@ietf.org
> Subject: [mpls-tp] Proposed liaison to ITU-T on G.8110
> 
> 
> Several people have pointed out a discrepancy in the model 
> for MPLS as documented in G.8110. Since this formal model 
> plays a major role in the ITU-T MPLS-TP G.8110.1 
> specification, the error should to be corrected before publication.
> 
> I therefore propose that we send the following liaison to the ITU-T.
> 
> - Stewart
> 
> ===============
> 
> To: ITU-T WP3/15
> From: IETF
> 
> Dear Dr. Trowbridge,
> 
> We note that G.8110 is referenced as a normative reference 
> from the draft text of the revision of G.8110.1. We also note 
> that G.8110 is now five years old, and has received no 
> contributions for update over that period. G.8110 has been 
> described as "not covering all of MPLS and certainly not what 
> has happened in the last five years."
> 
> We believe that G.8110.1 should document MPLS-TP accurately. 
> It is important, therefore, that where the model for MPLS-TP 
> differs from that described in G.8110, the correct model be 
> developed and documented in G.8110.1.
> 
> We would like to draw your attention in specifically to 
> Section 6.2.2 of G.8110 (and, in particular, Figures 1 and 2) 
> that says that the Time-To-Live (TTL) field of an MPLS header 
> is part of the Characteristic Information (CI) of an MPLS_CI 
> traffic unit. We note that according to G.805, the CI is 
> supposed to be delivered end-to-end between MPLS APs without 
> modification or inspection. But the function of a TTL in an 
> MPLS-TP network is to be decremented at each hop along the 
> path, and to be inspected at each hop and tested against 
> zero. Thus, in the model for MPLS-TP, the TTL should not form 
> part of the CI.
> 
> We request that G.8110.1 be updated to include this revision 
> to the model. This might most easily be achieved by 
> augmenting the references to G.8110 with updated figures 
> based on those in G.8110 along with appropriate text 
> explaining the differences in the model such that
> G.8110.1 correctly captures the model for MPLS-TP.
> 
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