User guide

Technician’s Handbook
194
Line protocols
Line protocols have the following behaviors:
Unguarded Clear: Similar to a standard home telephone
where the person handling the call is expected to either
• hang up before the other party does, or
• hang up after hearing dial tone or reorder tone (after
the other party hangs up).
Guarded Clear: Not supported on the current hardware.
CTR.21: Same as Guarded Clear, but allows for spurious
line breaks on initial connection.
North American: Release if a break of at least 500 ms
occurs in the line current.
Disconnect Clear: Release if a line break of at least 455
ms occurs in the line current.
The main difference between the North American line
protocol and the Disconnect Clear line protocol is the
behavior when a line break occurs.
North American protocol does not break the loop and
waits to see if the current returns. Disconnect Clear
protocol waits 60 ms before breaking the outgoing loop to
acknowledge the clear attempt. After a further 395 ms, it
reconnects the loop to check if the current has returned.
If not, it clears the loop.
3100 Hand.bk Page 194 Monday, August 19, 2002 8:49 PM