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Phase 2 system with Phase 1 revert

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Premium Subscriber
Nov 9, 2002
Asking for a friend...

The answer may be manufacturer specific, or delectable by manager, and I'm interested in all of those variables if you have them to offer.

A multi-site phase-2 system has phase-1 revert. A phase-1 user affiliates to a site and talk group. Does that talk group revert to phase-1 ONLY on the site where it's being affiliated? Or do all sites carrying that talk group revert. I'll take it one step farther -- the system has RF subsystems using two separate bands. Does this affect how the system would handle the revert?


Silent Key
Dec 19, 2002
Supply (Lockwood Inlet area), NC
Not sure if this helps but I found it interesting.

If I recall correctly, the subject of your question came up in any conversation/thread recently (I'd have to dig and find it). To my knowledge, at least for Motorola, when a talkgroup reverts, it reverts on all sites where the traffic is being carried (and/or radios are affiliated with that talkgroup). In that discussion, someone mentioned that Motorola has recently come up with a solution for the double bandwidth for the Phase 1 user(s) to be limited to only the site(s) where a Phase 1 user is affiliated.

I don't know if that's 100% accurate but if it is, it sounds like a Motorola specific thing - at least in the way it was presented.

If it is true, I wonder what this would mean for P25 vendor neutral systems.


There's stuff I can't tell you...
Jun 16, 2013
It depends on the system. Most systems currently will knock down the talk group system wide.

Just to make sure we are all on the same page, a Phase 2 control channel operates at 9600 bps using the same protocol as Phase 1 trunking. Phase 2 on the other hand uses two different modulation schemes for the non-control information. One for downlink and one for uplink. Downlink is at 12000 bps and uplink is 6000 bps IIRC.

So you have to gateway the two phases to convert between the CAI's in order to knock down just a single site in a multi-site arrangement. This takes hardware and/or licensing. Motorola recently announced the feature for Astro25. I believe only 7.17 will support it though but someone more up-to-date on Astro25 system releases will likely be able to confirm whether or not other releases will support it.


5B2_BEE00 Czar
Premium Subscriber
Jul 12, 2008
Cobb County, GA Stadium Crime Zone
7.17 will support transcoding over ISSI as well.

As it stands now, the "least common denominator" on 7.16 and below will dictate the mode of operation on DDM talk groups across multiple affiliated sites. One FDMA radio affiliated to the talk group forces every site with users affiliated to that talk group to downgrade to FDMA. This is true on ISSI.

My system has an ISSI8000 connection to another system within our foot print. Both our cores are 7.14 (at present, ours will be moving to 7.16 by 1st of next year as part of our SUA). and on our DDM talk groups provisioned as foreign groups on each others' core, if an FDMA radio registers on either core, the entire talk group becomes FDMA on both systems.

Really makes one think hard about allowing ISSI with connected systems that have alot of legacy radios. Can cut capacity in half.
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