How many talk groups in P25?

novascotian · Apr 7, 2015

I don't know much about P25 and am just getting used to our brand new 700 MHz system covering Nova Scotia. As far as I know this is a Phase 2 capable system operating in Phase 1. My question has to do with the number of talk groups there can be in the system. When I have looked this up the only answer I saw was 65536 talk groups, and 256 x 65536 UID's. There is an organized system here for giving out TGID numbers, i.e. agencies have a block to work within, and they are up in the mid 40000's so far, which is fine, but there is a chance, more than a chance really, that two other provinces will come in on this. I had expressed concern that with expansion the upper limit of 65536 will be quickly reached and will have to revisit the big blocks of numbers the existing users have. I was told in reply that there can be many more talk groups than 65536 in the system... So what is the actual limit?

Voyager · Apr 7, 2015

There is no template for TGIDs - they can be anything in the valid range. I've never heard of a P25 system running out of TGIDs yet. I've only heard of one Motorola system (OH MARCS) running out of them, and they only had 4096 TGIDs for the entire state.

W8RMH · Apr 7, 2015

Voyager said:
There is no template for TGIDs - they can be anything in the valid range. I've never heard of a P25 system running out of TGIDs yet. I've only heard of one Motorola system (OH MARCS) running out of them, and they only had 4096 TGIDs for the entire state.

Ohio MARCS is not a P25 system. Their highest TG is 65488 and used for radio maintenance if this gives any light.

I noticed on the NS system page they seem to be skipping a lot unless the OP has a more accurate list. To max out at 6XXXX is a lot of talk groups even on a large system.

KE5TLF · Apr 7, 2015

TGIDs = 16 bits
RIDs = 24 bits

Voyager · Apr 7, 2015

W8RMH said:
Ohio MARCS is not a P25 system.

That's why I said it's a Motorola system.

Also as I said, they only have 4096 TGIDs avaialble. They 'jump' since Motorola Type II systems use the lowest 4 bits as Status Bits, so TGs jump in steps of 16 (16, 32, 48, 64, 80, 96, etc)

(posting the second line more as a general reference, as I'm sure you know that fact, Rich.)

novascotian · Apr 7, 2015

Yes in the NS system they are skipping a tremendous number of TGID's For example the Halifax Fire Dept has ALL of the 30000's which of course is 10000 TGID's! They actually only have around 11 or 12 talk groups so that means 9990 or so that are skipped. You might say why... well what they have done here is give each agency the same range of numbers for TGID's and UID's (RID's) for neatness I guess. So for sure they have lots more radios than talk groups but still nowhere near 10000! They have given out subranges to the different stations... so the radios on the engine at Station 4 are numbered 30411 to however many there are on the truck... maybe like 5 or 6... and if there is no other truck at that station, that means that ALL the other 304xx numbers are unused... so yes there is a tremendous amount of skipping..

This is why I am asking,... as it seems like the system is going to run out of TGID;s unless they go back and fill in the gaps, which of course negates their neat and tidy system...

The answer re 16 bits for TG's.... I think that means 65536 maximum number of tg's..... just looking for clarification..

Voyager · Apr 7, 2015

It's called planning, and it sounds like they could use some of it.

WA0CBW · Apr 7, 2015

Don't confuse talk group ID's with subscriber ID's.
BB

16b · Apr 7, 2015

The Daniels Electronics P25 training guide (a long standing/well respected reference for P25) says the talkgroup ID range is $0000 to $FFFF hex (16 bits; 0 to 65535 decimal), just like KE5TLF said. The maximum number of talkgroups would be 65534 because TGID 0 isn't used and TGID 65535 is reserved for "all call" according to the document.

See http://www.dvsinc.com/papers/p25_training_guide.pdf

RKG · Apr 7, 2015

Just to add one more datum: in a SmartZone system (a/k/a "Type 2"), number of TGIDs available if priority is employed is 2047. When priority is used, least significant bit of TGID is dropped forced to 1, so only values ending in 1, 3, 5, 7, 9, B, D, or F (hex) are permitted.

INDY72 · Apr 11, 2015

And now with Smart Net and Smart Zones being discontinued the information is just for historical purposes anyway. Ohio MARCS is the original Smart Zone system now being fully upgraded to P25 the MARCS IP. As for other systems running out of TG/RID room... VIPER before the P25 upgrade, SAFE-T (now being upgraded to P25) just to name 2. With true P25 systems, it will be hard to overkill it with RID's or TG's, especially bigger systems with multiple cores/zones.

How many talk groups in P25?

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