Need help with performance on long-delay paths!

Need help with performance on long-delay paths!

Post by Doug A. Ch » Sun, 31 May 1992 04:47:52



I'm currently taking care of a WAN which includes a link between the US
and Japan.  The link currently has 256K bandwidth with approx. 128ms
round trip delay.  However, recently, our carrier had a undersea fiber
repeater failure and our link was routed over satellite.  Our 128ms
round trip delay became 600ms after the re-route.

Using rcp to copy files between the US and Japan nodes, our average
thruput on that 256kbps link w/128ms delay was about 120kbps.
That's about 50% utilization!  Not very impressive at all.

Now, when that link was routed over satellite, the thruput dropped to
33kbps (13% utilization).

FYI, here's our test setup:

            USA node                                    Japan node

   [PC]-----[ROUTER]-----[BWM]==================[BWM]-----[ROUTER]-----[PC]

PC: 386/33 SCO Unix machines
ROUTER: Cisco MGS
BWM: Network Express NE3000 Bandwidth Managers (additional bandwidth
        disabled)
-----: Ethernet
=====: 256kpbs link

1- What can be done to improve thruput under normal circumstances?
   (that is, over fiber with 128ms round-trip delays)
2- Is 'rcp' just not very good at handling long delay paths?
   (as far as I know, rcp is UDP based, so all flow control/error
    checking handled in rcp...)
3- What can be done to handle the really large delay situations?

4- Can anyone point out some other WAN test results/papers?

Thanks!
-Doug

 
 
 

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