Additional SIP channels listed but none in use

Can someone explain what is happening here - it looks like locked up sip channels. How do we stop this from happening?

Connected to Asterisk 1.2.16 currently running on iPBX-JEM (pid = 31250)
Verbosity is at least 10
iPBX-JEM*CLI> sip show channels
Peer             User/ANR    Call ID      Seq (Tx/Rx)  Form  Hold     Last Message   
192.168.1.108    108         196f386da2d  00101/651814663  g729  No       Rx: ACK        
192.168.1.100    100         61f44c3d091  00102/00000  unkn  No       Tx: ACK        
192.168.1.102    102         72e26ca80a9  00102/00000  unkn  No       Tx: ACK        
192.168.1.100    100         7924f00f110  00102/00000  unkn  No       Tx: ACK        
192.168.1.105    105         52fcceae5ac  00102/00000  unkn  No       Tx: ACK        
192.168.1.100    100         2fd07881688  00102/00000  unkn  No       Tx: ACK        
192.168.1.102    102         10e58ad03d6  00102/00000  unkn  No       Tx: ACK        
192.168.1.100    100         19a2d151011  00102/00000  unkn  No       Tx: ACK        
192.168.1.100    100         5b96015f7b8  00102/00000  unkn  No       Tx: ACK        
9 active SIP channels
iPBX-JEM*CLI> show channels
Channel              Location             State   Application(Data)             
IAX2/isphoneiax-3    (None)               Up      Bridged Call(SIP/108-b0231ac0)
SIP/108-b0231ac0     s@macro-sipprovider- Up      Dial(IAX2/isphoneiax/073881088
2 active channels
1 active call
iPBX-JEM*CLI>