Subject: RE: Why MPLS is called so

From: "Peter Tam" <[email-masked]>
Date: Thu, 4 Nov 1999 09:34:38 -0600

Hi,

At the end of tunnel (based on the Stack bit), MPLS control is turned back
to the L.3 network protocol as per the SHIM header. Currently it can only be
an IP SHIM. Ideally,  MPLS should be multi-protocol supporting any network
protocols not just IP. This area is not addressed and the mechanism to
identify which SHIM type is not yet standardized. IMHO, there are 2 possible
ways to define a SHIM type for a tunnel: use the 3 Unused bits in the MPLS
header. The cons are that everybody wants to get the hand on these bits. The
pros are that, on a single LSP, applications can multiplex and switch to
different network layer protocols (e.g. between IPX and IP) as they wish.
The other method is to create a SHIM TLV in the LDP/CR-LDP/RSVP+ label
signaling protocols to bind labels to network layer protocols at LSP setup
time. This TLV object should be optional defaulting to IP for backward
compatibility.

But, for now, who cares about multiprotocol apart from IP.

Regards...Peter Tam,
Nortel Networks, Canada

	-----Original Message-----
	From:	[email-masked] [SMTP:[email-masked]]
	Sent:	Wednesday, November 03, 1999 2:19 AM
	To:	[email-masked]
	Cc:	[email-masked]
	Subject:	Re: Why MPLS is called so

	Because the label switching can be done using any L2 protocol such
as ATM,
	Frame Relay, Etehrnet, FDDI and Point-to-Point links.

	corrections if any please...

	regards
	-- [email-masked]

	On Wed, 3 Nov 1999 [email-masked] wrote:

	> 
	> 
	> Hi all,
	> A very basic doubt...
	> Why is MPLS called multiprotocol?
	> 
	> regs,
	> Ravi.
	> 
	>

---

From: Eric Rosen <[email-masked]>
Date: Thu, 04 Nov 1999 10:45:20 -0500

Peter> At the end of tunnel (based on the Stack bit), MPLS control is turned
Peter> back to the L.3 network protocol as per the SHIM header. Currently it
Peter> can  only be  an  IP  SHIM. Ideally,  MPLS  should be  multi-protocol
Peter> supporting  any network  protocols  not  just IP.  This  area is  not
Peter> addressed and  the mechanism to identify  which SHIM type  is not yet
Peter> standardized. IMHO, there  are 2 possible ways to  define a SHIM type
Peter> for a tunnel: use the 3 Unused  bits in the MPLS header. The cons are
Peter> that everybody  wants to  get the  hand on these  bits. The  pros are
Peter> that,  on a  single LSP,  applications  can multiplex  and switch  to
Peter> different network layer  protocols (e.g. between IPX and  IP) as they
Peter> wish.   The   other  method   is  to  create   a  SHIM  TLV   in  the
Peter> LDP/CR-LDP/RSVP+ label signaling protocols  to bind labels to network
Peter> layer protocols at LSP setup time. This TLV object should be optional
Peter> defaulting to IP for backward compatibility. 

Actually, section 2.2. of  draft-ietf-mpls-label-encaps makes it quite clear
that the L3 protocol is to be inferred from the label value. 

I  believe that  draft-ietf-mpls-rsvp-lsp-tunnel  does have  an L3PID  field
which is used as part of the label request.

Peter> But, for now, who cares about multiprotocol apart from IP.

Indeed.