AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 232

Data Communications Support
They do not protect against glare, a condition that occurs when
They cannot provide reliable far-end disconnect for toll restriction.
A ground-start (GS) trunk is preferred for communication with outside
analog data stations. Ground-start trunks provide improved signaling
and reliable far-end disconnect for secure toll restriction.
The following kinds of outside ground-start/loop-start trunks can be used
for data communications:
Basic trunks
Wide Area Telecommunications Service (WATS)
800 service (inbound WATS)
Foreign exchange (FX)
Ground-start/loop-start trunks connect to ground-start/loop-start jacks on
the following types of modules in the control unit:
800 GS/LS
400 GS/LS/TTR
408 (LS trunks only)
408 GS/LS
400 (LS trunks only)
800 (LS trunks only)
408 GS/LS-MLX (Release 2.0 only)
2. A tie trunk provides communication between two telephone switching
systems. A tie trunk "ties" the two systems together, providing access to
all telephones or data stations on each system. Tie trunks are usually
used for data communication with analog data stations connected to a
system at a different location, such as a different floor of a building, a
different building, or a different city or state.
A tie trunk connects to a jack on a 400EM module in the control unit.
3. A Direct Inward Dialing (DID) trunk allows incoming calls to reach
specific individuals or facilities in the system without the help of a system
operator. DID trunks are available only in the Hybrid/PBX mode. A DID
trunk is used to receive incoming calls from outside analog data stations;
it is not used for outgoing calls.
A DID trunk connects to a jack on an 800 DID module in the control unit.
4. A DS1 trunk carries digital signals in the Digital Signal 1 (DS1 ) format.
The DS1 format multiplexes 24 Digital Signal 0 (DS0) channels of 64 kbps
each and one 8-kbps framing signal, for a total of 1.5444 Mbps. A DS1
trunk can be used for communication with outside digital or analog data
stations.
Outside Trunks
5-14
an outside call is made at the same time that an incoming call
arrives on the same trunk.