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

[mark seery <m_seery@yahoo.com>]

Norman Finn wrote:

> Neil,
>
> I think Pat Thaler's reply helps to straighten out this confusion, but 
> let me
> try, also.
>
> There is a *lot* of confusion about the words "end-to-end", and about 
> "transport layers".
> There are lots of ends in this picture, and there are layers and there 
> are layers.
>
> An 802.1Q VLAN bridge, and by extension, a P802.1ad provider bridge, 
> does NOT supply a
> "transport layer" in the same sense as IP-over-Ethernet or 
> Ethernet-over-IP.  This is
> because, at the data forwarding layers, VLAN tags are best though of 
> as extensions to
> the address space, not as additional protocol layers.  If you want to 
> call it a
> "transport layer", feel free!  But don't assume that VLANs are 
> equivalent to other
> "transport layers". 
Hi Norman, this is a key point and a key area of disconnect (which I 
think we have in IP-MPLS as well, though perhaps slightly less so in 
PW-MPLS). Service Provider's should consider this point carefully and 
decide whether it meets their needs or not.

> Bridges *do* guarantee a level of service.  They manage to do this by 
> guaranteeing the
> quality of each bridge, and by *demanding* the quality of each link. 
Norman, just out of curiousity, how does 802 guarantee the quality of 
bridges, and even if you get the PW requirements you want in terms of PW 
link guarantees, do routers have to be changed, in your opinion, to 
provide the equivalent quality of bridges. Just trying to understand all 
the moving pieces you need to get what you would consider an Ethernet 
grade service.

Thanks,
mark


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