asterisk users - Jun 2007 - Zombie SIP channels

on sip show channels I do get a lot of entrys like

192.168.1.47     11          07ba5a490b3  00102/00000  unkn  No
Init: INVITE
192.168.1.47     11          19090f115b8  00102/00000  unkn  No
Init: INVITE
192.168.1.47     11          7d8b8fde46f  00102/00000  unkn  No
Init: INVITE


How do they appear?

How can they be removed? "core show channels" does not list them.

Elmar