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MERLIN LEGEND Communications System Release 6.1
Network Reference
555-661-150
Issue 1
August 1998
Introduction
Page 1-12Tandem Trunking and Tandem Switching
1
The advantages of tandem PRI facilities are illustrated in practical terms in
Chapter 2, “Call-Handling Scenarios.” However, tandem PRI trunks do present the
following challenges that affect your configuration planning.
■ Each PRI facility connected to a system, whether it is a tandem trunk or an
outside facility and whether or not drop-and-insert equipment is used
between systems, takes up 24 of the 80-line capacity of a MERLIN
LEGEND Communications System.
■ Each 800 NI-1BRI module takes up to 16 of the 80-line capacity.
■ Each 400EM tie module takes up to 4 of the 80-line capacity.
In view of this fact and the differences noted in Table 1–1
, we will briefly revisit the
private network configurations we looked at earlier.
The next three figures show basically the same configurations that you saw
before, slightly modified to emphasize the differences among them. The figures
shown are only a few examples for illustration, and do not represent all possible
configurations. In these figures, the lines and trunks literally represent the number
of facilities connected to each system in a given configuration. The PSTN facilities
shown here are only examples. You can connect the same types of loop-start,
ground-start, T1 Switched 56, DID (Direct Inward Dialing), and T1-emulated
analog lines/trunks to a private network system that you can to a non-networked
system.
SECURITYlALERT:
!
Do not connect T1-emulated loop-start lines or analog loop-start lines
without reliable disconnect to any switch that is part of a private network.
Touch Tone Receivers None
✔
Required for all calls routed across the
private network on tie trunks. (Voice
messaging increases traffic in both
directions.) Not required on PRI trunks.
Centralized Voice Messaging
■ Call information indicating
inside call
■ Message Waiting light updates
✔
✔✔
With PRI, the call information signals
sent by the remote system to the
centralized VMS indicates inside calls.
With tie trunks, the call information
signals for all calls indicates an outside
call.
With PRI, the Message Waiting lights are
updated on the signalling D-channel.
With tie trunks, Message Waiting lights
updates are sent as separate voice calls
and must compete with other voice and
data calls for an available tie trunk and
touch tone receiver. As a result, the
Message Waiting light updates may be
delayed on tie trunks.