The MPLS WG Archive

[Yangguang Xu <xuyg@lucent.com>]

Kireeti,

> 
> I don't get it.  Do you mean using LMP or similar mechanism for
> establishing the mapping?
> 

Yes and more. Neighbor discovery only discovery port association. Label
indicates finer granularity of physical resource. It includes both port ID and
channel/sub-channel ID. So it requires neighbor discovery + service negotiation
to form the label mapping between neighbors. The label mapping doesn't need to
be a table. It could be port mapping + some technology dependent rules.

> If a "data LSR" tells its neighbor to use label 272, the neighbor
> knows exactly what is meant.  If a SONET LSR tells its neighbor, use
> label foo, where foo is an encoding of the time slot to use, the
> neighbor knows exactly which time slot to use.  However, if a PXC tells
> its neighbor to use label bar, the mapping between "bar" and port number
> has to first be established.  The distinction is not data and non-data,
> but defined semantics for labels vs. dynamically established semantics.
> 

Sure, yet, there is a subtle difference. Label association in circuit switches
is hard-wired, while in PXC it's dynamic. 

Thanks,

Yangguang