What is format (nothing) in sip show channels

when I run sip show channels, sometimes I get something like this:

192.168.1.116 101 YTc4ZmM3NjV 00101/00006 0x0 (nothing) No Rx: ACK

what is codec format (nothing)? Is this an active or inactive call? Is it a call/connection about to be closed?

Thanx,

Michel.