Unresolve problem::network or server?

this problem happen last month..
before this all thing going well..
i'll start with the below network diagram

main office @

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@offshore platform

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@problem area (oil ship)


all server such as notes and dhcp located at main office..
user at op(offshore platform) and os(oil ship) connect to main office using satellite modem..both op and os have their own cisco router that connect derect to satellite modem..
connection at op is ok..all user can use note mail and login to novell client but user at os facing problem to access notes mail...
they can use other application that grab from novell client such as word, exel and lotus application.
for your information, each os and op have their own novell server at their side..
the problem now, user must wait about 20-30 minutes to login through notes mail...
user at main office don't have any problem using notes mail although their using the same server...
i suspect it not a LAN problem at oil ship because user can use other application except notes mail..
i also has change the swith with new one but still facing with the same problem..
i'll try to ping to notes mail at main office and local equipment and the result is like below::

os

---

> main office notes server = 547ms
os

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> os router <1ms
0s

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> os switch =1ms
os

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> os novell server <1ms

the internal diagram at oil ship is like below::


cisco router#

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cisco catalyst swth#

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novell server
| |
client(15 pc's)



do you have any idea what cause the problem?
is it the server or network?
how to troubleshoot it?

actually client pc connect to cisco catalyst not to cisco router...
sory for the mistake..