update of JSA for inter-domain diverse path & some simulation results

[ricciato <ricciato@coritel.it>]

Hi all,

please note that we have have updated the draft on the JSA  method for 
computing diverse paths in inter-domain.
We have also run some initial simulations on realistic topologies, 
comparing the 1) JSA approach (with ARO) with 2) the method based on 
RRO+XRO (called ISPA in the draft), and 3) the global optimum based on 
complete information.
We considered a few realistic topologies (details in the draft)
In summary the results show that :

- if a pair of diverse path exist, the JSA/ARO almost always find them 
at the first shot (it failed in 2-3 cases over thousands of simulation run)
- there are some topologies in which the ISPA/XRO is trapped at the 
first shot (and should therefore revert to cranckback), it happens 
approx. in 10% of cases
- when a pair of path is found by all the three methods, there is no 
substantial difference in the overall cost between JSA/ARO and optimum 
(we used min-hop metric), with a slight worse performance of ISPA/XRO

Please note that the performance of PCE should be the same as the global 
optimum (since it is computed assuming full global information and 
centralized computation).

Based on these preliminary results, we believe that the JSA/ARO approach 
should not be considered a competitor of PCE (which is provenly "the 
optimum"), but rather a secondary solution which achieves the same 
performances of the optimal method  "almost surely" in the practical 
cases  (still, it is possible to draw cases in which it fails, while 
PCE/optimum finds his way, but these cases seem to be not found in the 
realistic topologies we have investigated).
On the other hand the JSA/ARO  involves much  less information and 
signaling overhead...


In addition to the IETF site, the current version of the draft can be 
found at the following url. It includes quick  description of the 
simualtions and summary of preliminary results. It would be nice to have 
a short slot for presenting them at Washington DC, perhaps ....

We wellcome very much any feedback from the community that helps us in 
refining the simulation scenario (new topologies, suggestions for 
setting the scenario, etc.). Please do not hesitate to send you comment 
(particularly the criticisms, which are the most helpful ones for 
improving our work ...)

ciao
fabio

PS
the url for the draft is:

http://www.metanoia-inc.com/Publications/draft-dachille-diverse-inter-region-path-setup-01.txt