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

["Sprecher, Nurit (NSN - IL/Hod HaSharon)" <[e-mail]>]

Hi,

It is correct that the CI is transferred on a "network connection" which is formed by a series of contiguous "link connections" and/or "subnetwork connections" between "termination connection points". We should fix the proposed liaison accordingly! 

Still the concern is valid. 

G.805 refers to the generation (at the source), transport and termination (at the sink) of CI (in the context of a layer network), and also to the interworking of CI of one layer network with the CI another layer, but not to the processing of the CI at each transport entity or port along the network connection. 

Therefore I support the liaison with the correction of TCPs and not APs.

I think also that the fact that G.8110 (which is used as a normative reference) has not been updated since 2005, raises more concerns. MPLS was worked out since 2005 and there is a need to understand the gaps and check consistencies, etc. 

Best regards,

Nurit

 

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of ext [e-mail]
Sent: Tuesday, June 29, 2010 10:37 AM
To: [e-mail]; [e-mail]
Cc: [e-mail]
Subject: Re: [mpls-tp] Proposed liaison to ITU-T on G.8110

 

Stewart,

Whilst I don't agree with your proposed liaison I'd like to make a suggestion. Your statement that " We note that according to G.805, the CI is 

supposed to be delivered end-to-end between MPLS APs without modification or inspection" is incorrect by definition. CI information is transferred between Termination Connection Points (TCPs) and not between AP's. Indeed the point of the source termination function is to add information to adapted information which traverses the AP and thus to generate CI and the corresponding sink processes information.

 

This is quite clear from G.805 and is also well described in Sexton and Reid. I would therefore suggest you correct your liaison.

 

Regarding the model for TTL, I am sure that Q12 will be happy to explain the reasoning behind the way it was constructed and how the TTL value is decremented on a per hop basis. But perhaps it might be more appropriate to ask for an explanation of how the model works before assuming that it is wrong.

 

Best regards

Alan

 

> -----Original Message-----

> From: [e-mail] 

> [mailto:[e-mail]] On Behalf Of Stewart Bryant

> Sent: lunedì 28 giugno 2010 19.42

> To: [e-mail]

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

> 

> We note that according to G.805, the CI is 

> supposed to be delivered end-to-end between MPLS APs without 

> modification or inspection

> 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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> 

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