NT-4 Server: Is there a setting for network bandwidth "throttling" ???

[Some Guy]

I've got 2 NT-4 Server machines on a mixed network with about a dozen
other machines on a switched hub. All machines can access the
internet via a common gateweh (an ISDN modem) that is connected to the
hub. One of the NT servers (web-server) is running IIS 4 and the
other (pop-server) is running SMTP server software (post.office).

Other machines on the network can access (download) large files from
the web-server via www access and they can pull down e-mail (with
large attachements) from the pop-server with no apparent bandwidth
limiting or throttling.

However, from the internet side, while looking at real-time bandwidth
utilization stats being displayed by the ISDN router, the same pop-3
and www access to the servers appears to be throttled to something
approaching 25% of the full 128 kbs connection speed.

So my question is - Does NT-4 server have some sort of global machine
bandwidth limiting mechanism or setting, and if so where is it, and
can it differentiate between bandwidth restrictions on and off the
local network?