The MPLS WG Archive

[Chrysostomos Tziouvaras <tziou@ics.forth.gr>]

Mr Ashwood-Smith,
in your answer, cited below, you claim that a signal can be mapped from
one type of LSP to another type of LSP. I am using this in order to make
packet LSPs that traverse the optical network. 
But, is the mapping of LSPs a local decision for the ingress router of the
optical network? If it is, can he change this mapping dynamically without
notifying the initiator of the packet LSP?

Thanks in advance

Tziouvaras Chrysostomos
ICS-FORTH Researcher 

On Wed, 6 Dec 2000, Peter Ashwood-Smith wrote:

> 
>   Correct,
> 
>   One could take a signal and instead of using hierarchy, simply map it from one type to another of LSP.
> There is nothing in the generalized draft that precludes such translations. Actually if you go back a year
> and look at a draft that was presented we had something called a composite label that could change from
> type to type as it propogated. This work was subsumed by the generalized draft. While it is generally
> recognized that LSPs form a natural hierarchy, it is perfectly feasable to map from one type to another
> where the bandwidths are a close match, given that the hardware is capable of doing it. Such hardware
> is a hybrid LSR (we produce ATM/PPP examples of them today), which may change the label type as the 
> requests/path messages flow.
> 
>   This is most likely to occur with TDM and OXC equipement at the OC-192 and OC-48 rates where there is a
> close mapping between the OXC lambda and the TDM signal bandwidth. It won't work sell so well at lower rates
> because you waste too much bandwidth and are forced into a heirarchy whether you want one or not.
> 
>   Cheers,
> 
>   Peter Ashwood-Smith
> 
> 
>  
> > draft-ietf-mpls-generalized-signaling-01 mentions in the introduction a hierachy with fiber switching at the top followed by lambda, time-slot and packet switching and clearly distinguish between these levels. I don't agree with this view that a LSP starts and ends on the same LSR type and onyl nesting of LSPs of different LSR types is possible.
> > Take for example an optical cross-connect that switches fiber between its ports (=> fiber switch capable). The single or multiple lambdas on this fiber might be directly after the cross-connect or later combined with other signals from other fibers in a WDM system => (lambda switch capable) or a TDM technique is used to combine several of these signals to a higher bandwidth signal (e.g. going from 2.5 to 10 Gbit/s) (=> time switch capable). So a LSP that starts at LSC device ends up at a TSC device and might have a LSC device in between. Even an interchange of LSPs between packet and circuit switch capable devices is possible, take for a example circuit emulation via ATM. With circuit emulation you can also have a LSP that starts on a TSC device nested into a LSP that starts on a PSC device.
> > A LSP represents a connection through the network/sub-network for a certain signal. This is independent of the switching technologies along the route and at the end as long as the specific signal is supported. At both ends access to the specific signal has to be provided, but it doesn't matter if e.g. a 1.5 Mbit/s signal is transported on a time-slot of a TDM system, on a single wavelength of a WDM system (not economic), over a CDMA radio system or with circuit emulation over an ATM network.
> > The Hierarchy is defined by different signals nested into each other (client/server relationship), but not by the switching types.
> > 
> > Regards
> > 
> > Juergen Heiles
> 
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