The MPLS WG Archive

[Maarten Vissers <mvissers@lucent.com>]

Juergen,

As indicated in my previous email, LSPs seem to represent 3 items in the
functional domain:
	- end to end trail
	- tandem connection trail
	- tributary slot identifier.

Up to now, tandem connection trails are viewed as being additional
monitoring overhead/OAM within the same layer network as the main
signal.

	E.g. VC-4 and VC-4 Tandem Connection (TC-4), ATM VP end to end
	connection and ATM VP segment, or ODU1 Path and ODU1 Tandem
	Connection.

But within GMPLS with its "generic LSP" concept, we could view a VT1.5
as being a tandem connection LSP of the DS1 LSP for connection setup.
Similarly, we could view MS64, RS64, ODU2, OTU2 and OCh as tandem
connection LSPs of the VC-4-64c LSP for connection setup.

I believe that we are already doing something like this in SDH; e.g. the
set up of a E1 (2 Mbit/s) circuit is realised by means of setup of a
VC-12 trail.

Ofcourse, it is not possible to terminate a ODU2 LSP signal at a RS64
LSP endpoint. And it is also not possible to continue a ODU2 LSP via a
RS64 LSP in general; only if RS64 signal is in payload of ODU2 the ODU2
LSP "can be continued" as a RS64 LSP. Otherwise, e.g. if GFP (with IP or
ethernet) is in the ODU2 payload, RS64 LSP can not be used as
continuation LSP.

Regards,

Maarten

Heiles Juergen wrote:
> 
>         [Heiles Juergen]  Hi Yanguang,
> 
> > Juergen,
> >
> > Agree in concept,
> >
> > LSPs don't have to starts and ends on the same LSR type. A not ugly example is,
> > in circuit switched transport network, a T1 equivalent LSP can go through a TDM
> > mux and then a SONET box capable of low order switch.
> >
> >
>         [Heiles Juergen]  your example raises another question I have in my mind for some time. The T1 and the lower order VT1.5/VC-11 belong to different layer networks. The VC-11 is the server for the T1 signal accoording to the functional architecture. So basically we have two LSPs, a T1 and a VT1.5/VC-11 LSP with the T1 LSP partially transported within the VT1.5/VC-11 LSP. It is a one-to-one client/server relationship as the VT1.5/VC-11 transports only one T1 signal. Due to the one-to-one relationship it is possible to treat the two LSPs as one for the path setup. A more extrem example is a VC-4-64c (STS-192c-SPE) transported via an Optical Channel. The layer structure could be VC-4-64c -> MS64 -> RS64 -> ODU2 -> OCh, all with a one-to-one client/server relationship. Cross-Connections would be possible at the VC-4-64c level (SDH/TDM cross-connect), the RS64/OS64 level (fiber cross-connect), the ODU2 level (ODU/TDM corss-connect) and OCh level (lambda cross-connect). Do w!
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e set up
> !
> !
> one LSP or multiple LSPs, one for each layer and pass the set-up request from the client to the server?
>         If we have a many-to-one client/server relationship (multiplexing) it is clear that we generate a new LSP. Note that a layer network can have both one-to-one and many-to-one relationships, both as a server and as a client (e.g. a STS-1-SPE/VC-3 can transport a single DS3 or multiple VT1.5/VC-11).
>         Any view on that.
> 
>         Juergen
> 
> >
> >
> 
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