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76 Handbook of Intercom Systems Engineering
exists for the trunk master to route a signal from A to C and from C to B, thereby
bypassing the bottleneck.
Figure 5.8
Cascaded Trunking
Another advantage of trunking is that there is no requirement for the individual matrices
involved to be in close proximity. Systems, which are hundreds or even thousands of miles
away, have been successfully trunked using techniques described earlier with respect to
remote keypanels. Trunking is nearly identical to those situations, requiring the
transmission of a single data signal and the appropriate number of audio signals.
Note
A series of articles written by Andy Morris and Ralph Strader, on trunking at NBC,
appeared in Broadcast Engineering magazine in 1996. These articles, as well as an article
on Trunking Supervisory Systems by Robert Streeter and Thom Drewke of NBC, in PDF
format, are included on the CD.
A final methodology for distributing large matrices is a function of the manner in which
multiple ADAM™ frames are interconnected. When two ADAM™ frames, each 128
ports, are connected together, they become a single 256-port intercom system. The
interconnect between the two frames is through a Bus Expander, which transports all 128
ports between the two frames without rendering any of them unusable for keypanels.
The physical interconnect between the frames with bus expanders can either be via a pair
of coaxial cables, which can be used for distances up to 1,000 feet, or via a pair of fiber
optic cables, which can run for over 1,000 meters. The signal sent over the fiber or coax is
a multiplexed data stream, running at approximately 220 megabits/second. Since this data
rate is lower than the 270 megabit CCIR-601 serial digital video standard, many of the
asynchronous devices that can transport serial digital video can be used for this signal to
achieve even greater distances.