Subject: RE: Ethernet Circuit Types

From: "Vach Kompella" <[email-masked]>
Date: Thu, 25 Jul 2002 16:10:04 -0700

Putting Eric's and Stewart's replies together, I get the following reasoning:

A PW carries ethernet packets.  It doesn't and shouldn't care whether there are
VLAN tags in the packets or not.  So there should be only one such.

The NSP at each end does care about whether there are tags and what to do about
them.  Getting the NSP functions mismatched is a bad thing.

The signaling of which VC type to use may have an additional "which NSP should
we use" option.  This would allow one to signal the match or mismatch of NSPs
(not unlike whether or not one end supports the control word, or the MTU).  The
VC is operationally down until these things are fixed because we can catch them
at setup time rather than have them blow up in our faces at run time.

Signaling stuff like NSPs is an L2VPN function.  Signaling stuff like MTUs is an
L2VPN function.  Etc.  Therefore, draft-martini-trans should move to the ppvpn
WG, and include the NSP as an interface parameter.

-Vach

---

From: Luca Martini <[email-masked]>
Date: Fri, 26 Jul 2002 17:19:43 -0600

Shahram Davari wrote:

> Luca,
> 
> One needs different encapsulation modes, when:
> 
> 1) they can't be differentiated from each other, such as ATM cell mode and Frame mode. While the Ethernet VLAN tag can be parsed

> using the octet after the MAC addresses (If it is x8100, then there is a VLAN tag). or
> 
> 2) when they may be multiplexed in the same VC-LSP and therefore one can't
> use signaling to convey the treatment information for all PWs.
> 
> Which one is the case here?
> 
> -Shahram
> 

how about a 3rd option: principle of minimum intervention, and no insertion 
operation should be required.

1) above is not true for atm cell and atm frame , as one can always add a 
protocol field in the packet. this would mean an extra lookup ( parsing ) at 
the egress router. Ethernet has a protocol field , it's set to 0x8100 for Vlan 
tag. That does not mean that it's the same kind of transport. Of course it can 
be parsed , but that means extra work at the egress router for every packet 
received.
Converting every packet to non-tagged format means we loose information, namely 
802.1p bits.
So then are you suggesting we should only have a tag format ?

we could have only one ethernet format , which ingnores the 0x8100 flag.
Then we could signal the presence of the vlan tag.
then we are back to the original draft-martini design.
I don't care what you call the PW , the matter remains that the vlan tag 
presence needs to be signaled for MPLS PWs.
Doing extra lookup at the egress router is superflous and should be avoided.

Luca