Cisco Cisco IOS Software Release 12.3(4)T

The following restrictions apply to the Private Line Automatic Ringdown for Trading Turrets:

Before you can run the Private Line Automatic Ringdown for Trading Turrets feature, you must install 
an IP Plus image (minimum) of Cisco IOS Release 12.2(15)ZJ or a later release.

This feature is supported only for FXS loop-start ports and digital ear & mouth (E&M) immediate-start 
ports. When a voice port is configured with an incorrect destination number that may or may not be a 
valid number, the call may not perform as expected. There is no cross-checking for turret PLAR from 
the origination voice port, but there is a check on the terminating voice port to prevent accepting a call 
from a calling party that is not preconfigured.

To work properly, this feature must be configured at both endpoints in the connection (either FXS 
loopstart port or digital E&M immediate-start port).

To use this feature, you should understand the following concepts:

Private-line automatic ringdown (PLAR) circuits have statically configured endpoints and do not require 
dialing to connect calls. The connection plar command provides a mechanism to create a switched 
Voice over IP (VoIP) call without digit dialing. PLAR connections are useful where a telephone (or DS0) 
goes off-hook and a remote telephone rings (or remote DS0 goes off-hook) without digits being dialed. 
This feature is useful for: