talkgroup id spacing

[novascotian]

Pardon me if this is answered somewhere already. I monitor the Nova Scotia Trunked Mobile Radio System (TMR) which is a Motorola Smartzone system consisting of two zones and a total of 69 sites.

My question may be more general than for this system. My understanding is that Motorola tg id's are spaced 16 apart but with each tg id also made up of status bits [which I am not talking about in my questions today]. Here on the TMR the overwhelming majority of tg id's are spaced 32 apart based on a starting id of 00016 and going in the sequence 00016, 00048, 00080, etc.

But there are occasional tg id's that are the intervening ones, spaced only 16 from the others. In addition there is a relatively large block up in the 55000 to 58000 range that are in this in-between series... which one could say originate back in the series 00000, 00032, 00064, etc.

My first small question is really a side one.... is the first possible Motorola id 00000 or is it 00016? I suspect it is the latter.

My main question is regarding spacing. Am I right in assuming that any one system can have tg id's spaced 16 apart so that in theory there could be tg's from 00000 (or is it 00016 hopefully will be answered) all the way to the highest possible up in the 65000 range? Or is normal for a system to be like the TMR where the spacing is mostly 32 apart? but even if 32 spacing is the norm, why are there a few odd ones in between plus this large block mentioned above...?

 

[Jay911]

Others will have more complete answers, but yes, 16 is the lowest decimal TG you can see. The reason some agencies space their TGs further apart is usually for expansion purposes. i.e. if Fire, EMS, and Police all get talkgroups on the system, you might give Fire talkgroups under 20480, EMS from 20480 to 40960, and Police from 40960 to the end. That way, if Fire decides 2 years from now they need another talkgroup, they still have "room" to add it.

I believe the upper numerical limit in Type II systems is 4095*16, or 65520. That is, there can be slightly over four thousand talkgroups on a given Type II system.

For what it's worth, Uniden and perhaps RS/GRE are the only ones who use the decimal numbers (i.e. 65520 in the above example). Motorola numbers their talkgroups from 800001 to 804095 (sometimes with the leading 8 removed - don't ask why they use an 8). You can multiply the number after the 8 by 16 to get the "Uniden decimal" talkgroup. So 800004 is Uniden tg 64.

You might also see people represent a TG in hex values, where a "number" can be anything from 0-9 and A-F (base 16). So TGID 3CD = 800973 = 15568, for example.

 

[novascotian]

Thanks Jay.... for several answers in your reply! Still, I have to wonder why in this Nova Scotia system there are the few odd in between ones that do not relate to the ones around them. In fact I dont think there is a case where there are adjacent tg's only 16 apart. And the larger block I spoke of has only the in between series tg's in it and no "regular" ones. Why would the administrators do that.... It is as if they decided at the outset to go with 32 spacing beginning with 00016, but then someone forgot when giving out a few tg's or blocks of tg's. Thanks for clearing up that all could in theory be used in any one system... and that it starts with 00016 in a possible continuous series spaced 16 apart to 65520.

I was thinking also that maybe the Scanner manufacturers use the numbering system they do so that each status bit variation can have its own 5 digit number. So in your example 800973 comes out as 15568 but also with status bits the varieties 15569 to 15583. I cant think of any other reason, but I suppose there could be!

 

[RKG]

Let me expand a bit, referring to SmartNet II and SmartZone systems:

And, for convenience, let us limit ourselves to the hexadecimal system, which is what Motorola uses:

1) Talkgroup IDs are entered into subscriber radios (and zone and system controllers) as 3-digit hex numbers.

2) Talkgroup IDs are grouped into 7 "blocks":

Block 0 - 000h through 1FFh
Block 1 - 200h through 3FFh
Block 2 - 400h through 5FFh
Block 3 - 600h through 7FFh
Block 4 - 800h through 9FFh
Block 5 - A00h through BFFh
Block 6 - C00h through DFFh
Block 7 - E00h through FFFh

3) For SmartNet II and SmartZone, the hex "odd" TGIDs (i.e., ending in 0, 2, 4, 6, 8, A, C or E) are not used; this space is reserved for function of the "Priority Monitor" scan function. As a result, only 256 TGIDs are usable in each block, ending in 1, 3, 5, 7, 9, B, D or F.

4) When planning a system, it is not unusual to group a bunch of TGIDs together, leaving empty space between logical groups. For instance, the MassPort system, which uses primarily Block 0 TGIDs, starts at 001h for operations (7 TGIDs assigned followed by 9 TGIDs blank), then 021h for fire (5 TGIDs assigned followed by 11 TGIDs blank), and so forth. This is simply to leave room for future expansion or manipulation without going nuts trying to keep like things together (and to minimize the number of subscriber radios you have to touch for reprogramming). There are no hard rules on this and no real conventions; each system designer does things a bit differently.

5) Some radios display some hex values (such as UserIDs) as decimals, and generally add to the resulting decimal a value such as 800000. This is done (a) because the display will not show the alpha components of a hex number and (b) to pad out the field. For example, this is how MCS2000 mobiles show UserIDs. I've never encountered a Motorola radio that does this for TG IDs, though some older GTX radios actually program using decimal values (of the 3-digit TGID only, not the 4-digit TGID+SB format). For example, TGID 819h ("A PTL 1") on the Massachusetts state system would be entered into a GTX as "2073".

 

[RKG]

Others will have more complete answers, but yes, 16 is the lowest decimal TG you can see. The reason some agencies space their TGs further apart is usually for expansion purposes. i.e. if Fire, EMS, and Police all get talkgroups on the system, you might give Fire talkgroups under 20480, EMS from 20480 to 40960, and Police from 40960 to the end. That way, if Fire decides 2 years from now they need another talkgroup, they still have "room" to add it.

I believe the upper numerical limit in Type II systems is 4095*16, or 65520. That is, there can be slightly over four thousand talkgroups on a given Type II system.

For what it's worth, Uniden and perhaps RS/GRE are the only ones who use the decimal numbers (i.e. 65520 in the above example). Motorola numbers their talkgroups from 800001 to 804095 (sometimes with the leading 8 removed - don't ask why they use an 8). You can multiply the number after the 8 by 16 to get the "Uniden decimal" talkgroup. So 800004 is Uniden tg 64.

You might also see people represent a TG in hex values, where a "number" can be anything from 0-9 and A-F (base 16). So TGID 3CD = 800973 = 15568, for example.

Actually, the maximum number of usable TGIDs in a SmartNet II or SmartZone system is 256 * 8 = 2048.

 

[Jay911]

Actually, the maximum number of usable TGIDs in a SmartNet II or SmartZone system is 256 * 8 = 2048.

I did not know about the priority monitoring allocation part of things. That accounts for that.

Radio (user) IDs actually start with 7, i.e. 712345; radios can be any number from 700001 to 765534 in my experience. It's talkgroup IDs that start with 8, i.e. 800013 (for "decimal" tg 208 or "hex" tg D). I work with Centracom dispatcher consoles daily (the computer-based so-called "CRT" version), and it requires the 800000-series values when referring to TGIDs. RIDs (radio IDs) are referred to with the 7's.

 

[RKG]

I did not know about the priority monitoring allocation part of things. That accounts for that.

Radio (user) IDs actually start with 7, i.e. 712345; radios can be any number from 700001 to 765534 in my experience. It's talkgroup IDs that start with 8, i.e. 800013 (for "decimal" tg 208 or "hex" tg D). I work with Centracom dispatcher consoles daily (the computer-based so-called "CRT" version), and it requires the 800000-series values when referring to TGIDs. RIDs (radio IDs) are referred to with the 7's.

Again, this is the CentraCom translation of the hex values, and the 700000 or 800000 is added to pad the field. The trunked system itself uses the hex values.

 

[WayneH]

Actually, the maximum number of usable TGIDs in a SmartNet II or SmartZone system is 256 * 8 = 2048.

And if you aren't using Priority Monitor my understanding is you can use the full range. I seem to recall there being memory limitations that would keep you from actually assigning every single one in the SAC database.

 

[DonS]

And if you aren't using Priority Monitor my understanding is you can use the full range. I seem to recall there being memory limitations that would keep you from actually assigning every single one in the SAC database.

Where "full range" gives you one more bit (the lsb that's always 'high' in the lowspeed data), increasing the TG count to 4096.

 

[novascotian]

Regarding the 8 blocks as mentioned by RKG, is this blocking a convenience only or does it have some technical significance? I checked in the Nova Scotia system as I expected to see users or agencies confined within blocks but it turned out that series of TGID's in a couple of cases just went right on through the "boundaries" of blocks....

 

[RKG]

For the system designer and programmer, it is a matter of convenience. As a result, what you have reported is unusual.

For the system software, it is a matter of how the databases are structured.

For operations (both the zone/system controller and subscriber equipment) it is essentially irrelevant.

 

[WayneH]

Regarding the 8 blocks as mentioned by RKG, is this blocking a convenience only or does it have some technical significance?

I've never seen the standard 8 block partition table used for users; it's too wide in scope. When I do see it used is in assigning analog and digital talkgroups.

 

[slicerwizard]

The trunked system itself uses the hex values.

The controller, consoles, radios, everything, just use numbers. Hexadecimal is simply a display / entry format. The control channel, for example, doesn't send data in hex. Nor are radio IDs hex values, SmartZone systems aren't limited to the even talkgroup numbers, 700000 and 800000 aren't added to pad fields (they're used to disambiguate talkgroup IDs and radio IDs).