Re: [PWE3] once upon an erratum

[Stewart Bryant <[e-mail]>]

Sasha

Do you have the correct reference? If so perhaps you could
point to the right section.

Stewart


Yaakov

I think that the purpose of the text as to say that the tag
may or may not be service delimiting, which I think is
demonstrably true.

Stewart



On 08/05/2012 12:20, Alexander Vainshtein wrote:
>
> Yaakov, Stewart and all,
>
> I believe that 5061 effectively supports Yaakov’s point of view.
>
> My 2c,
>
> Sasha
>
> *From:*[e-mail] [mailto:[e-mail]] *On Behalf 
> Of *Yaakov Stein
> *Sent:* Tuesday, May 08, 2012 1:59 PM
> *To:* Stewart Bryant; [e-mail]
> *Subject:* [PWE3] once upon an erratum
>
> Stewart and all,
>
> RFC 4448 has an erratum marked "Held for Document Update by Stewart 
> Bryant".
>
> This erratum (penned by Alfred Hoenes) deals with several issues,
>
> from a "subtle typo" to the misleading figure label.
>
> However, there is one issue with which I agree and which I think is 
> important;
>
> but regarding which I don't recall discussion on the list.
>
> With the entire group of comments marked as "held for document update" 
> rather than as "approved",
>
> I am not sure whether this issue has been agreed upon.
>
> The text in question is this :
>
> When the PE receives an Ethernet frame, and the frame has a VLAN tag,
>
> we can distinguish two cases:
>
> 1. The tag is service-delimiting. This means that the tag was
>
> placed on the frame by some piece of service provider-operated
>
> equipment, and the tag is used by the service provider to
>
> distinguish the traffic. For example, LANs from different
>
> customers might be attached to the same service provider
>
> switch, which applies VLAN tags to distinguish one customer's
>
> traffic from another's, and then forwards the frames to the PE.
>
> 2. The tag is not service-delimiting. This means that the tag was
>
> placed in the frame by a piece of customer equipment, and is
>
> not meaningful to the PE.
>
> Alfred states that
>
> The term, "service delimiting", apparently here is defined
> by the origin of the tag, not by its function.
>
> I understand where the original text comes from.
>
> In the provider provisioned model the SP doesn't trust the customer to 
> properly tag the frames,
>
> and so doesn't look at tags inserted by CE devices.
>
> However, other groups (e.g., MEF) assume careful prior negotiation
>
> (of the legal kind, not the protocol kind) between customer and SP,
>
> and so the C-tag may indeed be service delimiting.
>
> More specifically, one can make the distinction between three 
> "bundling" types
>
> based on the C-tag.
>
> *All-to-one means that all C-tags are taken as one "flow" or "EVC" or 
> whatever,
>
> and thus the mapping to PW is independent of this tag.
>
> So here the C-tag is NOT service delimiting.
>
> *One-to-one means that each C-tag is mapped to a single EVC.
>
> So the C-tag determines the PW, and is thus service delimiting.
>
> *Arbitrary bundling means we have a general mapping
>
> of C-tags to EVCs (and so includes the previous two).
>
> In general the C-tag here too is service delimiting.
>
> (NOTE: the arbitrary and One-to-one cases are lumped together in MEF as
>
> the "bundling" case.)
>
> Do you agree with this analysis, and thus with the need to remove the 
> caveat in 4448
>
> that states that C-tags can not be service delimiting ?
>
> Y(J)S
>
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