The MPLS WG Archive

["mark seery" <mseery@ix.netcom.com>]

----- Original Message -----
From: "Vishal M" <vishal_study@yahoo.com>
To: <mpls@UU.NET>
Sent: Friday, October 18, 2002 7:02 PM
Subject: DiffServ MPLS over Ethernet (L-LSP vs E-LSP)


> The reason for the doubt is:
> The Ethernet header (like ATM) doesn't have any QoS
> information field (unless 802.1q is supported). So
> does that imply that E-LSP can't be used when ethernet
> is the underlying media (and 802.1q is not supported).
>
> Is L-LSP the only choice then?

Vishal, the option to use E-LSP or L-LSP comes down to whether the MPLS
"shim" is used on the interface in question - or not. For FR/ATM it was
decided not to use the shim, and reuse the existing headers.

I can't see any standard covering Ethernet per se, but always assumed when
MPLS runs over Ethernet it uses the shim (which is different than mapping a
native Ethernet interface to a MPLS service), and
http://www.ietf.org/internet-drafts/draft-martini-ethernet-encap-mpls-01.txt
seems to infer MPLS shim can be used over Ethernet.

At any rate, unless there is a draft/standard which specifies reuse of
Ethernet headers for L-LSP in the same fashions as FR/ATM, then perhaps the
question you ask should be the other way around ;-)

Seriously, shim or no-shim is the crux of the issue - I haven't followed it
close enough recently to give u a definitive answer.

-mark

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