Telnet Timeout issue

Hello,

We have the servers inside our network that the employees can Telnet on. The session never time out.
We have a regional office from where the employees Telnet on the same servers but they have a timeout after 10 minutes idle time.
All the network devices are Cisco. The regional office is connected to headoffice via a VPN connection. The VPN is terminated on my Cisco Firewall.
Would somebody have any idea what the problem can be?

Thanks,
Mehdi