Dissertation Defense - Ming-Chit Tam

[David Farber <farber@central.cis.upenn.edu>]

    CapNet - Using a Gigabit Network as a High Speed Backplane


                        Dissertation Defense


                          Ming-Chit Tam




With their vast amount of bandwidth, Gigabit networks have effec-
tively shrunk communication delays to that of light wave propaga-
tion, opening the long waited opportunity to distribute  applica-
tions  across a wide area network. By connecting a number of high
performance computers together with a gigabit network,  and  pro-
viding hardware and software supports for a virtual memory shared
among these computers, we have effectively created  a  geographi-
cally  dispersed  multiprocessor  with a high speed but also high
latency backplane.


   The key to realize this system is to reduce the effect of  la-
tency  as  much  as  possible. While caching and replications are
well-known techniques to reduce memory access latency,  they  re-
quire mobile data and their copies to be located to maintain data
consistency. CapNet addresses this problem in the  context  of  a
wide  area  network  by embedding a set of intelligent mechanisms
into the network. Our approach is to distribute the location  in-
formation  of  memory  objects  and their copies into the network
switches so that the network can actively support cache coherence
protocols.  In CapNet, a write miss is handled by directly multi-
casting invalidations to the memory object copies which then send
back their acknowledgments. A read miss is handled by replicating
a copy from the copy holder that is geographically closest to the
requesting  host,  thereby reducing the traveling time of the re-
quest and its reply to a  minimal.  Our  approach  reduces  write
fault  delays  by  as much as 30% and read fault delays by 50% in
compare to the more popular directory based approach.






Supervisor: David J. Farber
Committee : Ruzena Bajcsy
            Hiromichi Hashizume  (NACSIS)
            Keith Ross
            Jonathan Smith (Chair)


            DSL Conference Room, Moore School
            9:00 am on 2 May 1994.




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