RE: decisions on L2 solutions documents

On Mon, 2003-06-02 at 21:30, [email protected] wrote: 
> Hamid Ould-Brahim wrote 02 June 2003 18:35
> 
> Peter, 
> > 
> > 
> > Wouldn't it be kind of cool if we could use the same 
> > addressing format for 
> > what ever MPLS LSP/pseudo wire/tunnel? Is it too simple to 
> > say we always 
> > identify the end-point of an LSP/PW/tunnel with a unique 
> > address (I mean 
> > unique for the LSP/PW/tunnel so no 2 PWs share the same address)? 
> > 
> But it that case how about pw created for l2vpns.
> NH=> Hamid why do you think you need PWs at all?  The only reasons PWs exist
> is as follows:
> -	to fix the problems caused by mp2p LSPs.....if you want any-any
> connectivity use a cnls mode, in a co pkt-sw mode only p2p and p2mp
> constructions make any arch sense....mp2p leads to problems and kludges;
> -	to keep the pretence-up that MPLS =~ IP.....if true why do we need
> MPLS then?  Use the right mode for the right application....both are
> required;
> -	to squeeze a bit of the server-layer BW via client compression (a
> total non-issue IMO when other technolgies squander BW).
[rest snipped] 

Meanwhile, back in the real world, PWs (in the MPLS context) do the
following:

1) add a label to the stack to keep state out of the core (this may also
create a p2p LSP on top of an mp2p LSP, depending on whether you are
using LDP or RSVP-TE for your tunnel LSPs).
2) create a bidirectional p2p construct out of two unidirectional p2p
LSPs.
3) adapt the layer 2 protocol being carried to MPLS.  This involves
three things:
i.   stripping off the layer 2 header (aka "compression") in the cases
such as FR where the header may be different at each end.
ii.  sequence numbering, if required, for the case where the core
network may reorder packets.
iii. length checking, for the case where the core network's minimum PDU
is larger than that of the PW (this is required because MPLS has no
length field).

Giles 
 
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Giles Heron    Principal Network Architect    PacketExchange Ltd.
ph: +44 7880 506185              "if you build it they will yawn"
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