# Loop start transmit signaling

With loop start interfaces, the transmitted signaling A bit in the signaling timeslot causes the interface to seize the line (go off-hook) or release the line (go on-hook).

If the A bit is set to 1, the line goes off-hook. If the A bit is set to 0, the line goes on-hook.

Bits B, C, and D are reserved, and should be set to 0.

The following illustration shows transmit signaling for loop start line interfaces:

Loop start transmit signaling

This table summarizes the transmit signaling for loop start line interfaces:

Bit | Hex bitmask | To take line off-hook | To put line on-hook
A bit | 0x08 | 0x08 | 0

If you reset the switch, all bits are set to 0.