[squid-users] outside squid link overload.

Hello Squid users.
 Long time had been spent looking for the solution. Still i have
nothing.
 We are mobile operator. I have many GPRS subscribers that are NATed
by cisco to one public IP address prior to go to squid-2.5.STABLE6-3.4E.5. The problem is that GRPS users start 2-3 downloads and Squid loads it very fast and put it to cache but user can load the objects from Squid only at 30-180kbit/s. So when I divert all GPRS users thru Squid, my internet link becomes stuck because Squid loads many files at all available bandwidth and then give it to customers at GPRS speed.
 Restriction by delay pool doesn't suit - users have different speeds (up to 230kbit/s), so if I restrict each to 230kbit/s - it won't help because 40kbit user will cause Squid to download at 230kbit/s. If I restrict to 40kbit/s, then 230kbit user will complain that speed is very low.

 Question: How to make Squid not to download a new part of file unless the old part is already loaded by the user?
 Tried cisco WAE612 as Content Engine - the same issue.

Here is a picture of Squid interface:

Sometimes traffic is equal. But some moments Squid loads from Internet (blue) more then gives to network (green). So network cannot timely consume the loaded traffic.
Please help.

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Alexey Kovrizhnykh