My local system, a P25 Phase 2, Motorola I believe. It has multiple sites, I noticed that frequently a talkgroup that is based out of one site, makes it to another site. So multiple times a day the same talkgroup is available in multiple sites at the same time. I was wondering why only part time. I heard roaming is a thing on some systems? How does this work? Does a user have the ability to set their radio to a talkgroup from one site while currently using a different site? Will it result in what I described?
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P25 Roaming?
- Thread starter nokoa3116
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All depends on system setup. If its multiple ASR or simulcast cells it can be different. Each talkgroup has a profile assigned. For a talkgroup to get assigned on a site it needs a radio affiliated. There are ways to map it to always TX on a certain site but normally only for certain reasons. Other talkgroups can be set to not roam on other sites. Lots of moving parts.
MTS2000des
5B2_BEE00 Czar
and then there is ISSI...to further add the moving parts equation
Why? System efficiency. Why push audio to a site that does not have a radio/talkgroup affiliated to it? (There are certain operational exceptions, and there is a system admin function to push audio to to sites w/o talkgroup affiliations. But this is used "surgically" as it is a resource/voice path burner)
"Does a user have the ability to set their radio to a talkgroup from one site while currently using a different site?" No. The radio affiliates ("Roams") from site to site. Based upon technical criteria. (Adjacent site signal strength as compared to current site, site preferences, etc) Once affiliated to , the radio is receiving all instructions via that site's control channel. (IE Does not rx adjacent site control channels)
I assume the radios affiliate and that’s when that happens. But from a scanner prospective the control channel I monitor get call grants for that talkgroup from a different site only at certain times. It mostly happens at night, or at times where there aren’t any active calls.
Someone taking their radio home with them at night, and they live in coverage of a different site than where that TG usually covers.
Or it could be related to nighttime dispatch consolidations (e.g. a dispatch center is closed 12am-8am and is covered by another area).
Thunderknight gives a couple of typical example. There are many others.
P25 systems have multiple ways to manage use/footprint. They can be managed via radio site access profiles, talkgroup site access profiles and/or a combination of both. Your system (Mileage) may vary.
Chance
Member
From a user perspective, they are given a radio and usually given an explanation of where it can be expected to work. They turn on the radio, set the knob to their channel and just expect it to work.
Let's say there are 3 traffic signal repair guys that work for Main County which are the only users of Talk Group 123. The P25 system spans the entire state. Main County has 3 sites. The system is configured to only allow Talk Group 123 users to operate in Main County. On Monday all 3 repair guys are working the same job and therefore only the closest site needs to carry their traffic. On Tuesday each of the 3 guys are at the 3 farthest edges of the county, so all 3 sites carry their traffic. On Wednesday, a worker that lives in Hick County calls in sick, but attempts to use his radio from home to get in touch with his colleague. He gets a BONK tone and NO SERVICE when he turns on his radio. This would be a typical configuration. A more critical user such as a Police Officer would likely be able to use their home talkgroup anywhere in the state, due to police chases, prisoner transfers, court, etc.
In another county, 5 volunteers firefighters go home to a different county each night. Instead of being able to take their expensive P25 radio home, they are issued a Unication Pager. Since Unication is receive only, it can't tell the local site which Talk Group it wishes to listen to. So the radio shop has made a special configuration for Fire Dispatch to always be carried on that site, regardless if any actual P25 radios are affiliated with that group on that site.
There are also simulcast sites which carry the exact same transmissions on the same exact set of frequencies simultaneously on all participating sites. It really just comes down to design and various needs. One reason to use a simulcast over multiple locations is maintaining only a single set of frequencies, versus having to maintain frequency allocations for each site. You can maybe get 10 frequencies to support the entire service area, versus 5 frequencies for each site. It all comes to calculating load factors. While towers in the simulcasts sites are geographically distributed, conceptually they are just another site that serves a given area that a user can roam to.
Let's say there are 3 traffic signal repair guys that work for Main County which are the only users of Talk Group 123. The P25 system spans the entire state. Main County has 3 sites. The system is configured to only allow Talk Group 123 users to operate in Main County. On Monday all 3 repair guys are working the same job and therefore only the closest site needs to carry their traffic. On Tuesday each of the 3 guys are at the 3 farthest edges of the county, so all 3 sites carry their traffic. On Wednesday, a worker that lives in Hick County calls in sick, but attempts to use his radio from home to get in touch with his colleague. He gets a BONK tone and NO SERVICE when he turns on his radio. This would be a typical configuration. A more critical user such as a Police Officer would likely be able to use their home talkgroup anywhere in the state, due to police chases, prisoner transfers, court, etc.
In another county, 5 volunteers firefighters go home to a different county each night. Instead of being able to take their expensive P25 radio home, they are issued a Unication Pager. Since Unication is receive only, it can't tell the local site which Talk Group it wishes to listen to. So the radio shop has made a special configuration for Fire Dispatch to always be carried on that site, regardless if any actual P25 radios are affiliated with that group on that site.
There are also simulcast sites which carry the exact same transmissions on the same exact set of frequencies simultaneously on all participating sites. It really just comes down to design and various needs. One reason to use a simulcast over multiple locations is maintaining only a single set of frequencies, versus having to maintain frequency allocations for each site. You can maybe get 10 frequencies to support the entire service area, versus 5 frequencies for each site. It all comes to calculating load factors. While towers in the simulcasts sites are geographically distributed, conceptually they are just another site that serves a given area that a user can roam to.
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hitechRadio
Member
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- Dec 23, 2010
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There are many reasons, as mentioned.
One reason to force a TG out a site with no affiliations for that TG on that site is for priority scanning purposes.
(Side Note: Many people do not realize the Scan Priority is also a function setting on the system side that must be set, for priority scan to work correctly in the radio itself, just setting a talkgroup priority in your radio does not make it priority if not enabled in the system. And you are limited to the number of TG's that can have priority monitor enabled in the system.)
Additionally, you may want to control what talkgroups are allowed at a site based on resources available at a site, example number of voice channels available.
The systems really are very configurable for different situations/needs.
One reason to force a TG out a site with no affiliations for that TG on that site is for priority scanning purposes.
(Side Note: Many people do not realize the Scan Priority is also a function setting on the system side that must be set, for priority scan to work correctly in the radio itself, just setting a talkgroup priority in your radio does not make it priority if not enabled in the system. And you are limited to the number of TG's that can have priority monitor enabled in the system.)
Additionally, you may want to control what talkgroups are allowed at a site based on resources available at a site, example number of voice channels available.
The systems really are very configurable for different situations/needs.
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