[squid-users] router hangs

Hi ,

i have a Zyxel router to which , my squid machine is connected.
There are around 150 users , whenever these users go through squid (at port
3128) , the speed is good for around 20-30 min. but after that the router
simply freezes.

But , when these users are given direct access there isn't any problem.
I have 1GB of memory, and checked the usage through TOP, the memory is hardly
used when squid is running.

where else can i look into to see what's wrong ?

-- 
Regards,
Boskey Chheda