This document describes one reason why the analog phones attached to
the VG224 Voice Gateway, which registers to Cisco CallManager as the Skinny
Client Control Protocol (SCCP) gateway, receive no dial tone from the VG224
Voice Gateway when they are off-hook and provides a solution.
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The analog telephone attached to the VG224 Voice Gateway receives no
dial tone when the phone goes off-hook.
Figure 1 shows the topology of this
This problem is a configuration issue. It is related to idle battery
voltage. Foreign Exchange Stations (FXS) need to supply DC battery and AC
ringing to enable the connected telephone equipment to transmit speech energy
and to power the ringing device of the telephone equipment.
The show tech-support command output shows
that the FXS idle voltage is set to low (see the arrow A in Figure 2). This is the root cause of the
Figure 2—Partial Output of the show tech-support
The solution is to set the FXS idle voltage to high (see arrow A in
Figure 3) when you configure each individual voice
port on the VG224. This changes the idle voltage from -24 volts (low) to -48
Figure 3—VG224 Sample Voice Port