"Hybrid" phase I or II system

[Technoguy58]

I have been checking some sites in a neighboring state using pro96com an have noticed that some of the rural sites show as being Phase I while most of the other sites and all in metro areas show as Phase II sites. This seems kind of like a "hybrid" type of setup. My question to the professionals, is this normal in a system as it is growing?? Just curious. By the way, this is a statewide P25 system.

 

[IAmSixNine]

It was probably set up as a Phase I system, perhaps a statewide system years ago and now that some of the major metro areas are upgrading their system to Phase II they are linking to the statewide system.
The general answer to your question is Yes, its normal. For systems that take years to implement like P25 Motorola used Phase I for many years, now that Phase II is the go to for public safety the systems coming online are now Phase II, which are backwards compatible with Phase I traffic.

 

[MTS2000des]

Most P25 systems implemented within the last 5 years are designed to be phase 2 capable.

The network I support is a phase 2 design with DDM (Dynamic Dual Mode) capability. DDM is a Motorola term, but other vendors also support this mode of operation. Basically it allows system owners to support both FDMA radios to join TDMA talkgroups. When an FDMA subscriber affiliates on a DDM talkgroup, the talkgroup is downgraded to FDMA so long as that one subscriber remains affiliated.

The downside to this mode is it reduces capacity of the system overall. For instance, my system is a 12 channel design, 1 is always a control channel, so in FDMA mode, that's 11 active talkpaths, TDMA allows for 22.

I am in the process of deploying new TDMA subscribers over the next few months, so while some talkgroups today may be FDMA, tomorrow they may show up as TDMA if only TDMA radios are affiliated with those talkgroups.

In the future when all users have TDMA capable hardware, we will most likely change from DDM to TDMA only. It can be done on a talkgroup by talkgroup basis from the NM client. The decision is one radio managers have to make carefully, as there is much legacy FDMA equipment in use in neighboring areas.

Your statewide system may be setup that way if your system core and sites are capable of TDMA. Today, subscriber radios may be older, but that could change as they are replaced with newer radios that are TDMA capable.

Some of those rural sites may be low capacity sites, and TDMA will enhance capacity and prevent wide area talkgroup busies caused by low density sites filling up with traffic.