Subject: Limitations overcomed by ARO

From: Cheng-Yin Lee <[email-masked]>
Date: Thu, 29 Apr 2004 12:18:09 -0400

Alessio, Marco, Ugo, Fabio, Vishal,

As I understand this draft overcomes the following
limitations:           
                  ".... we propose an alternative approach, based on the
joint
                  computation of the two paths in a distributed manner, 
                  which overcomes ..."
                 "... two main limitations:
                    - Trapping
                    - Sub-optimal route selection "

Could you please confirm if the following can be overcomed using the 
scheme described (quoted below) in the draft :
                  
* Can the path setup for the first LSP (computed by the head-end) lead
to trapping in the 
second area or sub-optimal route selection if the head-end node only has 
link state information of the first  areas
* Can an ABR in Area 1 & 2 compute paths to avoid  trapping in Area 3 if 
the ABR in Area 1 & 2 only has link states of these 2 areas?

                 "While the
                  path of the first LSP - that is, the one being
installed during the
                  first phase - is included in the ERO, the route of the
second LSP -
                  which will be installed in the second phase û will be
collected in
                  the ARO during the first phase itself. At the end of
the first phase,
                  the ARO collecting the e2e route of the second LSP is
returned to the
                  head-end node, which can then install it as an
ER-LSP." ?

* Can a head-end node in AS1 avoid trapping in the network if the
head-end node only knows 
about link states in AS1 and the virtual links to other ASes?

                 "... can model a multi-AS network.  
                 ... JSA minimizes the number of areas that 
                  the two LSPs share, and if two area-disjoint paths are
present in the 
                  network, JSA can compute them;"

                 "Node A computes two disjoint paths between itself and
B, 
                               within area 1, with a inter-area
topological view as 
                               shown in Fig. 5b; in this case, node A
MUST prune all 
                               the border nodes, except one for every
area connected to 
                               area 1, before the disjoint route
selection algorithm is 
                               performed; as a result, the two LSPs will
not cross the 
                               same next area, and will follow the
computed inter-area 
                               path.

Thanks
Cheng-Yin