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DCI Talkgroup Control Details
(Talkgroups for Dummies)
KerChunk.net  -  PushToTalk.us

 

PTT is short for "Part Time Talkgroup" or "Push To Talk" and is simply a method to "trigger" a talkgroup active and/or inactive on the timeslot.

 

Talkgroup control or PTT is sometimes a difficult concept to understand.  This page should explain the process so that a DCI repeater user is able to become familiar with the PTT technique as well as to be able to effectively harness the power of PTT.

PTT can enable or disable the linking of talkgroups based a on a brief transmission or kerchunk on a particular talkgroup of interest.  Normally a PTT enables that talkgroup active on the timeslot but more importantly, it disables the other talkgroups that could go active on the network side.  This provides a local repeater user with "exclusive" use of the timeslot for some short period of time without concern of another talkgroup high jacking an active local conversation.  PTT works both on full time or part time talkgroup.

That is it and little more.  But that "little more" part can actually accomplish quite a lot and that is the crux of the benefit as well as the source of some frustration.  What this page will provide the reader, hopefully, is more clarity or a better understanding, on what really is happening under the covers of the DCI c-Bridge.  The Bottom line


Master Control Talkgroups

These talkgroups are special purpose and carry no voice traffic.  They will override the conventional "timer" based programming discussed below.  Newly created c-Bridge managers (IPSC network repeater groups) will be based on this Master Control Talkgroup (MCT) concept while older managers will keep their hold-off timers as the primary method of talkgroup manipulation.  Some managers may have some combination of the two methods implemented for the full time talkgroups to further enhance the repeater user's experience.  Local 1 and Local 2 can also be used to supplement MCT Off's with shorter but automatic hold-off timers typically with 10 minute off cycles.

More info on MCT's and how to code and use them.  The rest of this page discusses the more common method to control talkgroups on DCI and many other c-Bridges.

 

Ground Rules and Assumptions for Hold-off Timer based Talkgroups

  • TRBO allows only a single talkgroup to be active on a timeslot at any one time on any one IPSC network or repeater.  There is no audio "mixing" as in analog remote bases/repeaters.  This means there is only a single voice channel at a time on each timeslot is permitted.

  • TRBO can support many talkgroups for use on a timeslot but only one will pass and that is first-come, first served.

  • Let's begin with 3 Talkgroups in our example.  Let's call them Bridge 2, Comm 2 and TAC 310-2.  Interestingly, these are real life examples on DCI.  (Example Table below)

  • In the following example;

    • Bridge 2  and Comm 2 are full-time talkgroups on timeslot 2 and "always on", by default

    • TAC 310-2 is normally off (unlinked) but enabled part-time via PTT; activated for 15 minutes

Active Mode

  • If you hit the pickle (quick PTT) on TAC 310-2, then TAC 310-2 goes active, is linked or turned on.  An "on timer" begins to run, typically for 15 minutes of listen time.  At the end of the 15 minutes of listening, the TG is turned back off.  If you PTT at any time during the 15 minutes, the timer is renewed for another 15 minute period.  So if you are in an active conversation, the TG stays on or is linked continuously.

  • However, another control is embedded in that same PTT on TAC 310-2.  It is almost as important as the turning on of TAC 310-2.  TAC 310-2 has unlinking controls for the other 2 TG's in this example, Bridge 2 and Comm 2.  Every time you PTT on Midwest 2, you turn off Bridge 2 and Comm 2 for a short period, typically 3 minutes.

  • As long as you are actively talking on TAC 310-2, the off timer renews the 3 minutes of off time on Bridge 2 and Comm 2.  The reason this is important is that only 1 TG may be actively passed into and out of your repeater on timeslot 2.  If Bridge 2 and Comm 2 were not unlinked for this short 3 minute period, then your conversation on TAC 310-2 could be preempted by Bridge 2 or Comm 2.  That would be frustrating for a user in a QSO to have that potential of other TG's going active and hijacking their active QSO.

  • So remember, a PTT typically turns on one TG for 15 minutes while turning off other TG's for 3 minutes to reduce these potential preemptions.  This is the typical functioning of a part time or PTT TG control cycle.  And it applies to most of the talkgroups that may appear on a timeslot, which could be far more than used in this simple example.

  • Not all c-Bridge administrators bother with the hold-off timers as it can involve adding hundreds of timers but DCI does do this for all TG's in most cases, or full-time TG's in most cases, though occasionally no hold-off timers as noted in the talkgroup matrix.

Passive Mode

  • Once you PTT on TAC 310-2 and you choose to listen, you will now be monitoring TAC 310-2 for 15 minutes and Bridge 2 and Comm 2 go off for 3 minutes.  You now will be monitoring all 3 talkgroups for the rest of the 15 minutes or what is now really the last 12 minutes (tolling of the 3 min HO's).  Whichever goes active first will pass to your repeater.  The others, if they also go active will pop up after the one before it goes silent...and on and on.

  • If no one on your local repeater keys up on any timeslot 2 talkgroups, then these 3 talkgroups will have an equal opportunity to go active, whichever one is first to capture the timeslot and only that one TG will be repeated.  Very simple and this is how most c-Bridge tend to handle multiple TG's on the same timeslot.  This is the basic set-up on most c-Bridges and their repeater networks.

Break-in Mode

  • If you wish to turn off an active talkgroup that is currently being used elsewhere on a different network, you can simply PTT on a talkgroup of your choice.  This is typically done when you want to make a call on a different talkgroup.  For examaple, you hear traffic on TAC 310-2 but you now wish to use Comm 2, simply PTT on Comm 2 while there is a transition between talkers on TAC 310-2.  This can be tricky if the talkers are quick keyers as you are likely to get bonked.  Short Group Call Hang Timers programmed at the repeater level helps facilitate this break-in capability (not all repeaters have short GCHP timers).

  • While you must catch a narrow window between talkers, you must also wait for the Group Call Hang Timer to toll.  MotoTRBO default time is 3 seconds.  All DCI repeater owners/admins are instructed to to use 1 second for their repeater's Group Call Hang Timer.  Some do not and that makes it more difficult to break in and you may need to wait for a longer opening or for the conversation to run it's course.  If urgent you could break in on the conversation and ask the current talkers to pause for 5 seconds or so and then you can PTT on your quest for Comm 2.  This is a worst case scenario, but still possible.

Caveats

  • The "on" and "off" timers ONLY affect talkgroups on the same timeslot.  As the bulk of the DCI talkgroups are on timeslot 2, PTT is aggressively implemented.  Timeslot 1 talkgroups are higher priority and so there are fewer on timeslot 1.  PTT use on timeslot 1 are more for priority control rather than timeslot 2's "first-come, first served approach.

  • If you channel hop and use PTT, then remember you are turning off multiple TG's for typically, 3 minutes.  Any activity that may have been active elsewhere will be held off for that 3 minutes unless you PTT your current talkgroup upon your arrival.  This will turn on that talkgroup immediately rather then waiting for the 3 minute timers to turn all the TG's back on.  You will then you will miss little traffic and be back to a "known state".

  • If you are not sure if a talkgroup is on or off, part-time or full-time, then hit the pickle to insure that it's on.

  • The PTT control is implemented at the end of a current active network users talk cycle.  While you can PTT to enable the "on timer", it wont become "linked" until the the current active talker stops his transmission.

  • The 3 minute timers were chosen as best average to minimize the loss of an active talkgroup (frustrating for the active user) but also not keep the other talkgroups unlinked longer than necessary (missing other traffic needlessly).

  • Some talkgroups have different timer periods, both on and off timers for special purposes but unless you know otherwise the specifics, consider the 15 minute On and 3 minute Off timers to be the default on DCI.

  • The repeater owner or administrator has been instructed to set their repeaters for a 1 second "Group Call Hang Timer".  This is important.  The 3 second default time will generally be too long to PTT in except for the most courteous of users.  Long time HF'ers tend to be an issue as quick keying is so common in HF operation.

  • Transmit Interrupt (TXI) is strongly encouraged on the DCI networks.  It enables you to be able to de-key an active talker as well as enabling your radio to also be de-keyed.  This will further enable smoother operation when making use of PTT.  It is not embraced by most other groups and users seldom even bother implementing the feature.  Please program it into all of your DCI channels if your radio supports TXI.

  • Only the local repeater PTT traffic controls the status of off-network or non-local repeater traffic on the local repeater.  If there is no local PTT traffic, then the incoming network traffic is allowed in on a first come (to the timeslot) first served (to you) basis.

  • 15 minute "On Timers" and and 3 minute "Off Timers" are typical on DCI but many other values can be used and that is based on their specific purpose and beyond the scope of this page.

  • It is important to remember that PTT only controls other talkgroups and links outside of your local repeater or IPSC network.  In other words, PTT has no direct affect on what is transmitted over your local repeater/IPSC network.  PTT will control what goes out from your local repeater/IPSC network or what comes into your local repeater/IPSC network.  But everything you do locally always affects the local repeater and network because it is connected before the c-bridge has access and therefore, the ability to control.  But once your PTT reaches the c-Bridge, your PTT can change everything going out from there or downstream of your local repeater or IPSC network.

  • Your local repeater should have its "Group Call Hang Timer" set for 1 second (not the 3 second default) for PTT talkgroup control to work best.  For example, the "Bridge 2" talkgroup is active but you wish to use "Local Net 2"; wait for the transmission to stop, wait for repeater's 1 second "Group Call Hang Timer" to toll, key up on "Local 2", if you get talk permit tones, you have un-linked "Bridge 2" (as well as several other networked talkgroups that are also on the same timeslot 2).  The 3 (actually DCI enables 5 minutes for Local 1 or Local 2) minute activity window renews with every PTT on "Local Net 2" and will continue to keep all talkgroups on timeslot 2, off so that you will not loose the use of Local Net 2.  If your repeater owner has not changed the "Group Call Activity Hang Timer" to 1 second, then it is very hard to break in between and you may need to wait for the conversation to clear or a long pause.

This page has shown a very simple (honest, it is a simple) example of PTT control.  Many variations and more complexity can be added into the controls including additional talkgroups, the weekly scheduler for talkgroup and receive only talkgroups.  If you understand this 3 talkgroup inter-relationship of control, then even with additional complexity, the basic control principals do not change.

NOTE:  TAC 310 operates somewhat differently in that both sides must hit PTT before a connection is created and that is why it is a considered a destination talkgroup and should be prearranged.  This is much like a telephone party line where anyone can join in on the connection, but typically, only the 2 parties are active in the conversation.  Still, it is also a good example (below) as to how a PTT style talkgroup can coexist with 2 full time talkgroups on the same timeslot.  Then just add 20 more possible TG's on timeslot 2 and you can appreciate more how DCI manages many talkgroups on 2 timeslots with, arguably, some finesse.


Example Table:  This table shows the active talkers affect on the other 2 talkgroups.  Bridge 2 and Comm 2 are on full time normally while TAC 310-2 is off unless it's 15 minute on timer has been activated via a PTT.

Active Talker TG Status TG Status Comments
Bridge 2 (fulltime) Comm 2 off TAC 310-2 off Turns off Comm 2 and TAC 310-2 for 3 minutes for each PTT
Comm 2 (fulltime) TAC 310-2 off Bridge 2 off Turns off TAC 310-2 and Bridge 2 for 3 minutes for each PTT
TAC 310-2 (ptt) Bridge 2 off Comm 2 off TAC 310 now on for 15 minutes unless key up on B 2 or C 2

Every time a PTT of TAC 310-2 is done on the local repeater, Bridge 2 and Comm 2 are held off for another 3 minutes.  This provides essentially a clear timeslot for the "active" use of TAC 310-2 without interruption by Bridge 2 and Comm 2 traffic.  TAC 310-2 will remain on for 13 more minutes after the last local traffic ceases allowing the "passive" use (listening to) of Midwest 2.  So even a PTT talkgroup is able to coexist with full-time talkgroups with a minimum of user frustration.  This approach enables many more talkgroups to coexist as well on the same timeslot.


Congratulations if you have read this far!

The Bottom Line

If your remember nothing else about talkgroup controls, then remember to simply switch to your talkgroup of choice, hit PTT to trigger that talkgroup active and you will then know you are listening to that talkgroup for 15 minutes minimum.  If you don't hear anything then announce your presence in a way that will compel a response and remember to say which TG you you are calling on as many users scan multiple talkgroups and may not see the active talkgroup on their displays. 

TRBO hams are like FM'ers, tend to listen but not necessarily respond to a kerchunk or simply to a tossing out your call.  Sometimes you may need to say that "the sky is falling" or that you just won the "Publisher's Clearinghouse $7,000 a Week for Life promotion" and does anyone out there want some of your winnings.

CLOSING THOUGHTS:  Some may feel that this PTT approach is needlessly complicating HAM DMR.  Others may feel that having only 2 or 3 talkgroups active 7/24 is a complete experience.  DCI's approach is to try to provide to each repeater owner or repeater manager an individual or custom set of talkgroups that fit the mold of the repeater owner or their group of repeaters.  No "one size fits all" is mandated.  It is up to the repeater owners or IPSC network admins to decide if they want 2, 15 or over 60 talkgroups that are available on the DCI c-Bridge.  Assuming one has a good understanding of MCT, PTT, On/Off timers and the scheduling of talkgroups, then good choices can be made so that the repeater owner can provide the best services for his users.

 

Revised: 02/17/2016 07:37

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