AT&T MERLIN LEGEND Installation & Maintenance Manual page 74

System Description
With the OPT/LS connection, glare is more frequent as the
volume of calls increases. (Glare occurs when a user tries to
make an outside call on a line/trunk at the same time an
incoming call is being received on that line/trunk.) In addition, if
system B (the LS interface) does not have Remote Access, only
the station(s) assigned to the LS facility on system B can be
accessed by system A.
Analog Tie-Trunk Connection
In an analog tie-trunk connection, the system A's 400EM module
is connected to system B's CU. On premises, this module can be
connected directly to system B if system B has similar tie-trunk
facilities.
For off-premises connection, the 400EM module can be
connected via the telephone company's facilities to system B.
The analog tie-trunk connection can be programmed for two-way
traffic or for one-way traffic (incoming or outgoing). The one-way
mode prevents blocked calls caused by glare.
Digital Tie-Trunk Connection
The digital tie-trunk connection joins the DS1 facility (the 100D
module) on system A to system B's DS1 facility. If system B is on
premises, the connection is back-to-back. To reach a remote
system, the DS1 facility connects via a channel service unit
(CSU) to the telephone company's facilities.
Networking Capabilities 1-43