RE: [PWE3] RE: [802.1] 802.1ad Customer FCS Retention

[neil.2.harrison@bt.com]

Hi Stewart,

<snipped>
> > 
> > Stewart,
> > If this is a valid analogy then every networking technology that 
> > relays some traffic unit between points A and B can be regarded 
> > as modelling a bridge.....and that does not seem a good 
> analogy to me.
> > regards, Neil
> > 
> 
> A bridge has certain filtering and path selection properties, so
> the PW is certainly not a bridge.
NH=> Agreed
> 
> A PW has the property that it does not transform the data (any
> transformation takes place in the NSP, and that is not part of the
> PW).
NH=> OK, but there is an adaptation between the client and the server....the flags, length and Seq No. fields are that adaptation function.
> 
> The data carried over the PW has no meaning within the context of
> the PSN that carries it,
NH=> I agree that a client layer should be transparent to a server layer.....but does the ECMP hack not violate this then?

> and from the point of view of the CE's
> the PW does not exist other than in terms of delay and error.
NH=> But surely any client->server encapsulation relationship has this property.
> 
> Therefore from the CE point of view, the PW is just a repeater.
NH=> As noted above, I believe we can extend this to any client->server encaps.
> 
> For the PW to be an adaptation function, one would have to assert
> that the contents of the PW had some meaning within the PSN.
NH=> See remark on ECMP above.....my observation however is that there are functions that lie between the client layer network and the server layer network (be this IP or MPLS), and in my mind these are an adapatation function.

regards, Neil

> I don't beleive it has, because we never communicate any context
> information to any object in the PSN (either by signalling or
> self description) which it can use to interpret the contents of
> the PW.
> 
> Stewart
> 
> 
> 

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