AT&T MERLIN LEGEND Installation & Maintenance Manual page 46

System Description
Tie Trunks
Tie trunks provide private communication between two systems.
Tie trunks "tie" the two systems together, making it seem that all
the telephones are on the same system. (See "Networking
Capabilities" in this chapter for more information on how tie
trunks connect to other systems.)
Tie trunks provide efficient communication between systems at
different locations. These locations can be different floors of the
same building, different buildings in the same campus, or
different cities or states.
Tie trunks can be added to the system via the 400EM module.
The 400EM module has four ports that must be programmed
individually by selecting trunk options and setting the DIP (dual
in-line package) switches, located on the front of the module, for
different signaling modes and types (see Figure 72).
The following tie-trunk options need to be programmed:
Direction
Two-way (factory setting). Calls can be made in either
direction.
Outgoing only. Calls can be dialed but not received (no
ringing).
Incoming only. Calls can be received but not dialed (no
dialing).
Signaling Type can be any of the following types,
programmed via the 400EM module. The type of signal can
be set separately for incoming and outgoing calls; for
example, a tie trunk can be wink-start for incoming calls and
delay-dial-start for outgoing calls.
Control Unit 1-15