HTTPS Disconnect with squid

[Noc Phibee Telecom <noc@xxxxxxxxxxxxxxxxxx>]

Hi

we have a problems with squid. We have a lot of user use squid in proxy 
for access
to a https site.

The problems: We don't know why, but the session close on the https site 
after ~20/30mn.
only on Squid 3;x, on a old squid 2.6 we don't have this problems

Anyone know if they have a timeout or other that can close the https 
connection ?

best regards
jerome