I suspect what we are seeing here is the patching of old and new radio
systems. For example - Boston FD Channel 1 (483.1625R) is being
patched to 800 Mhz Ch 81 and to 700 mhz Ch 71. Channel 71 is
provisioned (set up / configured) to operate in P25 mode on the new
Boston area 700 Mhz TRS. Channel 81 is set up to operate in analog
mode on the MSP TRS primarily using Zone 1. The various channels
(communications paths) are patched together via the fixed
infrastructure (computer gear at the dispatch center or master
controller).

The 800 Mhz channel can probably be set up to operate in either
digital or analog mode. The same holds for 483.1625R. I suspect that
the 700 Mhz talk groups can only operate in P25 mode.

It might be useful to remember how a TRS operates. You hit the PTT on
a portable radio. A data packet is sent to the master controller. The
master controller assigns a channel pair to use. The master controller
doesnt really care if traffic is analog or digital. And the master
controller doesnt really care how many other comms paths are tied to
any other comm paths. The master controller only cares that a channel
pair is assigned when a PTT request is received.

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