rescuecomm
Member
If data is coming from broadband, could P25 be configured for two voice channels?
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Why the rush to Phase 2 P25 when the D block is coming on line?
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mmckenna
I ♥ Ø
Not sure I understand the question.
P25 Phase 2 is two slot TDMA in one 12.5KHz channel. Like DMR, cram two voice paths into the same space as one.
As for using it for data, you can only fit 4.8KB/s in a 6.25KHz equivalent channel. Not very useful for anything serious. And as you suggested, 700MHz D block, aka FirstNet, was intended to be broadband data for first responders. It can also carry phone calls and PTT traffic.
P25 Phase 2 is two slot TDMA in one 12.5KHz channel. Like DMR, cram two voice paths into the same space as one.
As for using it for data, you can only fit 4.8KB/s in a 6.25KHz equivalent channel. Not very useful for anything serious. And as you suggested, 700MHz D block, aka FirstNet, was intended to be broadband data for first responders. It can also carry phone calls and PTT traffic.
And to add to that. . . there seems to be a dramatic lack of enthusiasm around the idea of using FirstNet as a primary, mission critical radio system for both data and voice; putting all one's eggs in one basket is just asking for trouble, especially when a for-profit enterprise is responsible for the system. There's more enthusiasm for having one's own voice system with FirstNet as data system.
rescuecomm
Member
Wasn't aware that slot 2 can carry voice. Any agencies doing this? I understand the importance of having dedicated dispatch and operation channels. How important is slow data?
RS
RS
It's unclear how familiar you are with P25 Phase I and Phase II trunking, vs P25 conventional
- P25 Conventional is FDMA, and therefore is only capable of one voice transmission per frequency
- P25 Phase I trunking is also FDMA, and also one voice transmission per frequency
- P25 Phase II trunking is TDMA, which means that all traffic channels are capable of carrying two voice transmission per frequency, divided into two alternating time slots
mmckenna
I ♥ Ø
Depends on what it's used for. In todays world, there's not a lot you can do with 4.8Kb. Good for AVL (Automatic Vehicle Location), some very simple uses, like OTAR, Over The Air Rekeying, where encryption keys are uploaded to radios, OTAP, Over the air programming, where radios can be programmed remotely. There's been a few other things done, but that's pretty much it.
Public Safety has much higher demands on their data systems now. The old days of running license plates over a slow terminal are long gone. Now they are uploading reports, running license plate readers, scanning the mag stripe on the back of the drivers license, uploading/downloading photos, fire agencies can pull up building plans, maps, etc. Not to mention computer aided dispatch, where dang near everything can be done over a computer and not so much reliance on voice traffic.
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A small agency I do two way radio work for has asked me about migrating to FNET for primary coms. I was not completely opposed to the idea except for the obvious question of reliability. My biggest issue is I would like to see a purpose built device for PTT if this is the case. They make the gateway (pricey), but to issue officers cell phones and expect them to use them as radios is not practical.
I've had good luck with Inrico radios and am half tempted to load the ATT PTT software on it and see how it works.
APXNext is used on FNET as a PTT only devise. I use my LEX11, however a you said it is also a cell. I rarely use the cell feature...mostly cause FNET has no coverage at my house.
mmckenna
I ♥ Ø
Yeah, a lot of the newer high tier public safety market radios are coming with LTE capability.
Project25_MASTR
Millennial Graying OBT Guy
P25 and data.
Originally there were three phases to P25.
Phase 1 (conventional and trunked voice/data via FDMA)
Phase 2 (trunked voice/data via TDMA)
Phase 3 (trunked data)
You can actually reference Codan's P25 User Manual from 2004 and see the original progression and keep in mind, Phase 1 trunking was just beginning to get off the ground in 2004. When you look at the fact that P25 was designed back in 1990's, the 4.4 kbps voice encoder that could be subbed for raw data was a decent amount of data. Especially when the traditional alternatives were 1200 bps to 9600 bps packet terminals. Motorola built a system to add onto their P25 systems called High Performance Data (HPD) as a predecessor and it allowed up to 32k of on dedicated trunking resources (all controlled from the site control channel). However, cellular quickly surpassed what we now refer to as "Narrowband IP solutions" and is why Phase III is now defunct.
That being said, there are a lot of things you can do with P25 when it comes to data...but the systems are most efficient when using pre-canned statuses and call alerts and paging. You see it used some, but not often (for example, call alerts are used to open some gated community gates on GATRRS).
Originally there were three phases to P25.
Phase 1 (conventional and trunked voice/data via FDMA)
Phase 2 (trunked voice/data via TDMA)
Phase 3 (trunked data)
You can actually reference Codan's P25 User Manual from 2004 and see the original progression and keep in mind, Phase 1 trunking was just beginning to get off the ground in 2004. When you look at the fact that P25 was designed back in 1990's, the 4.4 kbps voice encoder that could be subbed for raw data was a decent amount of data. Especially when the traditional alternatives were 1200 bps to 9600 bps packet terminals. Motorola built a system to add onto their P25 systems called High Performance Data (HPD) as a predecessor and it allowed up to 32k of on dedicated trunking resources (all controlled from the site control channel). However, cellular quickly surpassed what we now refer to as "Narrowband IP solutions" and is why Phase III is now defunct.
That being said, there are a lot of things you can do with P25 when it comes to data...but the systems are most efficient when using pre-canned statuses and call alerts and paging. You see it used some, but not often (for example, call alerts are used to open some gated community gates on GATRRS).
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