This is a read-write setting that tells the router which in-band signaling scheme the two ends of an ATM call are using, so it knows how to interpret the ABCD signaling bits embedded in the voice payload. An admin configures this to match the signaling convention used by the connected telephony equipment, since misinterpreting these bits can break call supervision such as detecting on-hook/off-hook events. For example, if a PBX uses a particular ABCD bit convention for hook-flash detection, the admin sets this object accordingly so the gateway correctly reads those signals.