DMR Tier-II - Multi site configuration

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qmsarge

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I am trying to understand the DMR Tier-II in more detail. My current understanding is that DMR Tier-II is basically a "repeater based" Digital Mobile Radio (Tier-I being simplex). If my understanding is correct DMR Tier-II also allows a multi-site operation mode. That is multiple repeaters at various locations in a region, but all connected through an IP (Internet) back bone.

In DMR Tier-II multi-site mode of operations:-
1. How are the frequencies assigned? Will each of the repeater in each site have a different frequency?
2. How will a station (especially mobile station) know which repeater (within the multi-site repeater system) is the best to use at any given time?

If there any internet references explaining the DMR Tier-II multi-site installations & workings please do give me a link of the same.

Thanks in advance.
 
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kayn1n32008

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I am trying to understand the DMR Tier-II in more detail. My current understanding is that DMR Tier-II is basically a "repeater based" Digital Mobile Radio (Tier-I being simplex). If my understanding is correct DMR Tier-II also allows a multi-site operation mode. That is multiple repeaters at various locations in a region, but all connected through an IP (Internet) back bone.

More or less correct

1. How are the frequencies assigned? Will each of the repeater in each site have a different frequency?

Frequencies are assigned by repeater coordination bodies. If geographically separated they can be the same, if not separated far enough, they would need to be different.

2. How will a station (especially mobile station) know which repeater (within the multi-site repeater system) is the best to use at any given time?

The same way you would with an analogue linked system. You can tag the frequencies with a call sign, frequency, Mountain name, club name or what ever you want that will give you an indication of where the repeater is, and if you are with in its foot print.

Motorola allows a function called ‘roaming’ where repeaters beacon at set intervals, this allows the subscriber(mobile or portable) to determine which repeater has the strongest signal. Majority of ham based DMR will not do this though.




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popnokick

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More or less correct



Frequencies are assigned by repeater coordination bodies. If geographically separated they can be the same, if not separated far enough, they would need to be different.



The same way you would with an analogue linked system. You can tag the frequencies with a call sign, frequency, Mountain name, club name or what ever you want that will give you an indication of where the repeater is, and if you are with in its foot print.

Motorola allows a function called ‘roaming’ where repeaters beacon at set intervals, this allows the subscriber(mobile or portable) to determine which repeater has the strongest signal. Majority of ham based DMR will not do this though.




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Hytera repeaters support proprietary roaming, as well as Motorola. The AnyTone AT-D878 supports roaming that they say can be used with ANY Tier II DMR repeaters... not just Moto and Hytera. Can anyone reading explain their experience with that?
 

wrath

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More or less correct



Frequencies are assigned by repeater coordination bodies. If geographically separated they can be the same, if not separated far enough, they would need to be different.



The same way you would with an analogue linked system. You can tag the frequencies with a call sign, frequency, Mountain name, club name or what ever you want that will give you an indication of where the repeater is, and if you are with in its foot print.

Motorola allows a function called ‘roaming’ where repeaters beacon at set intervals, this allows the subscriber(mobile or portable) to determine which repeater has the strongest signal. Majority of ham based DMR will not do this though.




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Sure we have it but you have to listen to the analogue repeater I'd every ten minutes.
Repeater coordination requires that in most instances the repeater pair your using is at least 100 miles from another user of that pair and the chances of interfering with each others operation is minimal . We sometimes have band openings that allow freak things in my fire department we would sometimes be in the middle of a drill evolution and our pagers would go off ,there was a fire department in VA testing it equipment but with a band opening we would get there calls .
There is a primary on DMR that you can buy on Amazon, the problem being people short cutting the test by memorizing and moving into digital without a basic knowledge of analogue , It happens more and more these days ,if you know radio and it's limits it helps in the digital realm ,all digital basicly is , narrow banding what being required of business radios, but since there was a glut of Motorturbo equipment being phased out years ago from commecial service hams found a use for it and matter of fact have given DMR a larger exposure ,so much so that the Chinese started dumping cheap DMR radios and making a profit , there are still areas that CCRs are not welcome ,if you dont have a repurposed old part 90 Motorola the "purist" dont play with you. But all there digital modes in radio be it dstar ,fusion,P25 ,DMR, NXDN are all various digital compression narrow band schemes ,dstar and fusion are the earliest examples of systems designed and built for amateur use , Whereas the other are repurposed commercial junk that was cheap and easy to buy , the problem comes in down the road as this stuff reaches critical mass and breaking nobody is really making new DMR equipment on the level of the equipment being used eventually it will end it's usefull life and people will have to move from DMR to a more usable ham format gear ,they don't make gear with the duty cycle stability like the old stuff .

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qmsarge

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Thanks for the detailed responses. Is there a hard & fast rule that a frequency can have only 2 Talk Groups (Time Slot 1 & Time Slot 2) associated to it? Or can I have multiple talk groups added to the Time slots. And the Time slots would get assigned to the Talk groups in a round-robin fashion?

Eg:-
Time slot 1: TG1, TG3, TG5
Time slot 2: TG2, TG4, TG6

And the transmissions (from the repeater on a single frequency) would be like..
Time slot1.TG1
Time slot2.TG2
Time slot1.TG3
Time slot2.TG4
Time slot1.TG5
Time slot2.TG6
Time slot1.TG1
.....
Time slot2.TG6

PS: In many tutorial videos I saw multiple talk groups getting associated with a channel (which I understand to be a repeater frequency).
 

popnokick

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Multiple talkgroups may be assigned / used on any time slot, but only one talkgroup can be in use on a given timeslot at any given time.
 

qmsarge

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Multiple talkgroups may be assigned / used on any time slot, but only one talkgroup can be in use on a given timeslot at any given time.
So is it that the repeater decides which talk group would be active on a Time slot at a given time? I mean if I have 4 talk groups assigned to Time slot 1 the repeater will first give a chance to TG1, and then Time slot 1 to TG2 etc.? That is in a "round robin fashion".
 

kayn1n32008

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So is it that the repeater decides which talk group would be active on a Time slot at a given time? I mean if I have 4 talk groups assigned to Time slot 1 the repeater will first give a chance to TG1, and then Time slot 1 to TG2 etc.? That is in a "round robin fashion".

Not exactly.

The subscriber keys up and tells the repeater what talkgroup and slot it wants to talk on and the repeater rebroadcasts it. With DMR you can have two simultaneous conversations at once. The repeater is actually fairly dumb and just does what it’s told. It does however coordinate the two time slots so that the subscribers are in sync with the proper time slot and does not transmit over the other time slot.


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qmsarge

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Not exactly.
The subscriber keys up and tells the repeater what talkgroup and slot it wants to talk on and the repeater rebroadcasts it.
Thanks. So taking this scenario further:-
Step 1: A user keys up and tells the repeater (A) the talkgroup and the slot. The repeater listens for the Tx from the user (on the Time slot).
Step 2: The repeater (A) then re-broadcasts the message to the talk group which was the intended receipient. The repeater (A) also sends out the message on the IP (internet) network to other repeaters.
Step 3: Other repeaters (B) gets the message and see if it is for a TalkGroup which they have promised to Rx/Tx. If yes, they too broadcast this message on the TalkGroup and on the slot which they have configured for that talk group. Radios listening to the TalkGroup (and on the chosen time slot) on other repeater (B) would also hear the message.

Since all this happen within micro seconds, none of the users actually see any delay. Is my understanding correct? :)
 

kayn1n32008

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Thanks. So taking this scenario further:-
Step 1: A user keys up and tells the repeater (A) the talkgroup and the slot. The repeater listens for the Tx from the user (on the Time slot).
Step 2: The repeater (A) then re-broadcasts the message to the talk group which was the intended receipient. The repeater (A) also sends out the message on the IP (internet) network to other repeaters.
Step 3: Other repeaters (B) gets the message and see if it is for a TalkGroup which they have promised to Rx/Tx. If yes, they too broadcast this message on the TalkGroup and on the slot which they have configured for that talk group. Radios listening to the TalkGroup (and on the chosen time slot) on other repeater (B) would also hear the message.

Since all this happen within micro seconds, none of the users actually see any delay. Is my understanding correct? :)

Yes.


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popnokick

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There is a minor delay.... usually never worse than several seconds and often much less. And the delay will vary depending whether you are monitoring the local or distant repeater in the QSO. Listening to some QSOs may help you understand... and you can do that online at Brandmeister.network via their service called "HoseLine" http://hose.brandmeister.network
 

qmsarge

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Then what happens in this scenario:-
1. Repeater (B) has two talk groups (TG1 and TG2) configured to be used with Time slot 2.
2. Repeater (B) is also connected with Repeater (A) to Rx/Tx on TG1 and connected with Repeater (C) to Rx/Tx on TG2.
3. At the very same time, Repeater (B) gets traffic/messages on TG1 and TG2. How does Repeater (B) decide which message should go out?

popnokick said:
Listening to some QSOs may help you understand... and you can do that online at Brandmeister.network via their service called "HoseLine
Thank you. Would try to listen into, during the week end.
 

popnokick

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Only one TG can be active at a time on any time slot, even if multiple "static" talkgroups are programmed for that time slot. If the repeater is transmitting something from TG2 on TS2... and something from TG1 arrives at the repeater...... it simply is not transmitted if both TG's are assigned to TS2. When a repeater is transmitting or receiving on a timeslot it does so for only one talkgroup at a time. This is why network admins and repeater operators request that statewide talkgroups be used as "calling channels" and QSOs be moved off to "TAC" or local TGs. If a statewide TG is set as static on a repeater's timeslot, every transmission ties up that timeslot from being used by others for calling. If every repeater in the state has the statewide TG set as static, then a user key-up on that TG keys up every repeater in the state. This is also why "static" talkgroups must be chosen ... and used... with care.
 

kayn1n32008

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Then what happens in this scenario:-
1. Repeater (B) has two talk groups (TG1 and TG2) configured to be used with Time slot 2.
2. Repeater (B) is also connected with Repeater (A) to Rx/Tx on TG1 and connected with Repeater (C) to Rx/Tx on TG2.
3. At the very same time, Repeater (B) gets traffic/messages on TG1 and TG2. How does Repeater (B) decide which message should go out?

IP linked repeaters don’t work like that. If they are all linked, what ever is using slot 1 will also be transmitted on the other repeaters slot 1.

So if on repeater (B) S1-TG1 and S2-TG2 are active, they will also be transmitted over (A) and (C), and anyone trying to access the system should get a denial until the slot they want is free.


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qmsarge

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popnokick said:
If every repeater in the state has the statewide TG set as static, then a user key-up on that TG keys up every repeater in the state. This is also why "static" talkgroups must be chosen ... and used... with care.
kayn1n32008 said:
IP linked repeaters don’t work like that. If they are all linked, what ever is using slot 1 will also be transmitted on the other repeaters slot 1.
That clarifies it :). So when repeaters are linked up, it is never in a one-way scheme and every repeater exchanges its traffic both ways to the repeaters connected to it. Which also kind of ensures that only one person can talk to one talk group at a time. From what I understand a "busy channel lock out" feature exists in DMR Tier II systems as well.

And the scenario which @popnokick mentioned also makes repeater interlinking a good system to pass messages all across a state (or a big geographic area). Some thing like a "trunk channel" which can be used for emergency purposes.
 
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Project25_MASTR

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Essentially. The big thing which should be noted, if a TS is busy in a traditional Tier II arrangement, and another group remotely accesses that timeslot on a repeater where it isn't busy, message will never be received on by the users listening to the repeater who's timeslot is busy with another group's activity.

Where this changes is where you begin to get into the proprietary trunking and Tier III trunking formats.
 

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Project25_MASTR said:
The big thing which should be noted, if a TS is busy in a traditional Tier II arrangement, and another group remotely accesses that timeslot on a repeater where it isn't busy, message will never be received on by the users listening to the repeater who's timeslot is busy with another group's activity
Thank you, and this was one big question which I had in my mind. So as per my understanding:-
1. Repeater A has got two TGs on TS2; TG1 (which is also configured on Repeater B) and TG2 (which is also configured on Repeater C).
2. There is traffic on TG1 (as some one using Repeater B started talking). Repeater A, TS2 would now start Tx-ing this message.
3. Within nano-seconds there is traffic on TG2 (as some one starts using Repeater C). But Repeater A would NOT Tx this message, as it is already busy with Tx from TG1. So listeners of TG2 on Repeater A, will miss this message.
4. Repeater D also is a subscriber to TG2 on TS2. But repeater D would Tx this message, as it does not have any other traffic on any other talk groups. Listeners on Repeater D would be able to receive the message.

Where this changes is where you begin to get into the proprietary trunking and Tier III trunking formats.
Got it. So it means that if the requirement is that multiple talk groups need to remain in constant contact, and the geographical area is wide so that multi-site repeaters are required, then Tier III (trunking) is the only way out. But if the requirement is more simpler; just two groups (TG1 and TG2), but it has to reach a wider area then Tier-II multi site option would also work out. The two groups would be configured in the same time slots on each repeater in multi-site configuration, and they all would be connected over IP. The moment there is Tx on one Talk Group all repeaters in multi-site would simultaneously Tx it (in the same Time slots).
 

kayn1n32008

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Thank you, and this was one big question which I had in my mind. So as per my understanding:-
1. Repeater A has got two TGs on TS2; TG1 (which is also configured on Repeater B) and TG2 (which is also configured on Repeater C).
2. There is traffic on TG1 (as some one using Repeater B started talking). Repeater A, TS2 would now start Tx-ing this message.
3. Within nano-seconds there is traffic on TG2 (as some one starts using Repeater C). But Repeater A would NOT Tx this message, as it is already busy with Tx from TG1. So listeners of TG2 on Repeater A, will miss this message.
4. Repeater D also is a subscriber to TG2 on TS2. But repeater D would Tx this message, as it does not have any other traffic on any other talk groups. Listeners on Repeater D would be able to receive the message.

In a multi site Tier 2 system the repeaters all carry the same traffic on both time slots.

If repeaters are transmitting on TS 2, TG 1, no one else can use TS 2. Period. If someone try’s to transmit on ANY TG on slot 2 they *should* receive a denial tone, and not be able to transmit until the slot is clear.



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Project25_MASTR

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In a multi site Tier 2 system the repeaters all carry the same traffic on both time slots.

If repeaters are transmitting on TS 2, TG 1, no one else can use TS 2. Period. If someone try’s to transmit on ANY TG on slot 2 they *should* receive a denial tone, and not be able to transmit until the slot is clear.



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Yes and no, it really depends on the network configuration. Some vendors have repeaters which can have timeouts set to stop passing traffic on a talk group from the network if the repeater hasn't been keyed locally on that talk group since the timeout expired. Sometimes it's an additional network appliance which handles this (such as the C-Bridge) and is commonly used on the DMR-MARC system.

Got it. So it means that if the requirement is that multiple talk groups need to remain in constant contact, and the geographical area is wide so that multi-site repeaters are required, then Tier III (trunking) is the only way out. But if the requirement is more simpler; just two groups (TG1 and TG2), but it has to reach a wider area then Tier-II multi site option would also work out. The two groups would be configured in the same time slots on each repeater in multi-site configuration, and they all would be connected over IP. The moment there is Tx on one Talk Group all repeaters in multi-site would simultaneously Tx it (in the same Time slots).

Yes, if you don't want to miss activity, you need to utilize a trunking setup such as XPT, Linked Capacity Plus, Connect Plus, Capacity Max (or another TIII standard). If one site doesn't have an available resource to pass the TG traffic, it'll busy out the call until a resource is available at all sites the talk group is being used. However, you don't see that in the amateur world.
 
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