Neil, you wrote
- LDP induced LSPs do not really create a layer network.....since they
allow merging, and this in itself causes some hard QoS problems....like how
does one define availability in a mpt-pt tree? [Its the old issue of 'no
free lunch'...if you push down a problem in 1 dimension (eg scalability), it
creates a problem somewhere else (eg measuing availability in VPNs say)];
- Explicitly routed LSPs on the other hand do form true layer
networks....since they need to be signalled they exist as true trail objects
in their own right.
I'm not sure the existence of merging or QoS is necessarily a criteria for excluding LDP "induced" LSPs as a layer. Intuitively it strikes me that for the purposes of MPLS a layer can exist independently of which subset of topological constructs in the architecture toolkit it subscribes to. ER-LSPs overlaid on an LDP infrastructre using integrated routing to me would constitute a useful definition of a "layer". It is only when I ruthlessly exclude absolutely everything but the elemental p2p undirectional trail from the discussion that such a hard definition applies, unfortunatley much of the value statements around MPLS disappear at roughly the same time.