Hi Seifeddine,

The IP Phone 3911 does not have a local switch for PC Connection. The 3911 is comparable to the EOL 7902 and newer 7906 as far as functionality goes. There is some good info and a diagram in this doc;

Cisco Unified SIP Phone 3911 Administration Guide for Cisco Unified Communications Manager 6.0 and 5.1

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/3911/6_0/english/administration/guide/3911stup.html#wp1062797

Hope this helps!

Rob