Understanding IDAS Trunking

EricCottrell

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Hello,

Some useful scribbles as programs decoding IDAS become available.

The Icom IDAS Trunk System is an all digital form of an enhanced LTR system. There is no defined control channel and a slow rate data steam (SACH) is used for control information. Much of the same terminology and trunking techniques of an enhanced LTR system apply to an IDAS system.

IDAS is defined in Parts 1-E and 1-F of the NXDN Technical Specifications. There are some differences between the over-the-air data (CAI) between IDAS defined in Part 1-E and NexEdge/Conventional defined in Part 1-A. Very dry reading.

There are three types of systems possible with IDAS, a single site system, a multisite system linking mutiple sites together, and a intersystem system linking multiple mutisite systems together.

The System ID is split between an Intergrator Code (0 to 15) and System Code (0 to 32767) with 1-1 being a default value.

Site Ids have a range of 1 to 250 with reserved values of 0 and 251 to 255.

A LTR style Area bit is used in place of the Radio Access Number (RAN).

LTR style Repeater numbers are used with a range of 1 to 30. 0 and 31 are used for special purposes, like indicating end of transmission, or all repeaters are busy.

LTR style radio ids are used with the home repeater portion replaced by a subgroup prefix with a range of 1 to 30. This is tied to a home repeater on single site systems. The prefix of 0 is used as a filler or to indicate a user from another system on a intersystem system. The group portion has a range of 1 to 2000 for normal groups with 0 used as a filler. 2047 is used to indicate all groups and 2001 to 2046 are used for special ids and purposes.

A home repeater will send a burst of data every 2 seconds or so. It is quite sparse on a single site system with just an Idle message. A site in a multisite and intersystem system will send the Site Id and Adjacent Site information.

A multisite and intersystem site will also have a collect repeater that will send a burst of data every 2 seconds or so. The main traffic on the collect repeater will be registration of radios as they roam between sites. Voice traffic can be carried on the collect repeater if all the other repeaters at the site are busy.

73 Eric
 

EricCottrell

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Hello,

On IDAS Multi-Site systems, the system sometimes sends Site Channel Information to the radio when it registers on the collect channel. DWR messages are used. The Header message indicates the destination and block count. The Packet Frame (PFr) and Block (Blk) in the data messages decrease together with each data packet with zero indicating the last packet. Up to 15 blocks can be sent. The block can be retransmitted if the radio did not receive it. Here is an example of Site Channel Information.

Code:
Sync:  -NXDN48    mod: GFSK inlvl:  8%  IDAS Ch DATA  DWR (Header) SI:0-0 DI:1-757 BlockCount:3
Sync:  -NXDN48    mod: GFSK inlvl:  9%  IDAS Ch DATA  DWR (Data) PFr:2 Blk:2 00 25 F1 14 1A FC CC 58 1B 49 17 98 16 1B 91 92 48 1B
Sync:  -NXDN48    mod: GFSK inlvl:  9%  IDAS Ch DATA  DWR (Data) PFr:1 Blk:1 DD DD 88 17 1A EE AF 10 1B 3A FA 50 1A 1A F6 B1 D8 1B
Sync:  -NXDN48    mod: GFSK inlvl:  8%  IDAS Ch DATA  DWR (Data) PFr:0 Blk:0 42 FD 18 84 A6 6F 5F 00 00 00 00 00 00 00 00 00 00 00
The calculator program can be used for hex to decimal conversion. There are three blocks in the example and all three blocks were received.

The first two bytes (0025) are the length of the opcode and data, excluding the checksum. The length is 37 bytes. A value of zero means none and a value of one (opcode with no data) is reserved.

The next byte (F1) is the System Data Opcode. The upper four bits (F) is the Integrator Code, in this case 15. The lower four bits (1) is the opcode. 1 indicates Site Channel Information.

The repeater information follows taking up 9 bytes for each repeater. A length of 37 indicates 4 repeaters, 4 = (37 - 1) / 9. The repeaters seem to be always specified in repeater number order.

The next byte (14) is the Repeater number of the first repeater. The upper 3 bits are reserved and set to zero. The first repeater is Repeater Number 20.

The next 4 bytes (1AFCCC58) is the Transmit Frequency of the first repeater in Hertz. The first repeater transmits on 452775000 Hz or 452.775 MHz.

The next 4 bytes (1B491798) is the Receive Frequency of the first repeater in Hertz. The first repeater receives on 457775000 Hz or 457.775 MHz.

This site has the following repeaters:
Repeater 20 Tx 452.775 MHz Rx 457.775 MHz (and going through the rest of the entries gives the other three repeaters)
Repeater 22 Tx 462.525 MHz Rx 467.525 MHz
Repeater 23 Tx 451.850 MHz Rx 456.850 MHz
Repeater 26 Tx 452.375 MHz Rx 457.375 MHz

The 4 bytes that follow the repeater information (84 A6 6F 5F) is the Checksum. Zero bytes are used to pad out the rest of the packet.

73 Eric
 

WayneH

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NOTICE

I've stuck this thread to better aid folks in understanding how this protocol works. Lets keep the help requests to their own threads and leave these for technical discussion of the protocol's operation.
 

jeatock

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FYI: IDAS trunking is available as type 'D' (Distributed) and will have type 'C' (Control Channel) systems available. Both can be 12.5 or 6.25 KHz. Icom and Kenwood are (or will be 1st Qtr of 2015) ready to start shipping cross compatible equipment. Type-C systems are being introduced to the dealers now during I-A's road shows. Get ready - here it comes!
 

bainino

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Hi

Only for information.

I think all the ICOM digital products label it as IDAS systems, but for a time it use different digital protocols.

In US use the NXDN protocol with its proprietary modifications.

In Europe the older equipment uses NXDN protocol, but the newest equipment uses dPMR protocol.
 

Jay911

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Hi folks,

The latest version of DSDPlus FastLane has identified an IDAS system near me, and I'm trying to figure out some things for the benefit of submitting it to the RRDB.

1. No sysid or site ID is shown in DSD. Talkgroups and RIDs however are prefaced with a 2- (TG 2-11, RID 2-66, etc). Looking at the actual log file, the idle bursts show "Area=0". I gather from Eric's original message on this thread, Area is similar to RAN and the '2' is an indication that that fleet/TGID's "home channel" is 2? So I have a single site system, and for my purposes I guess the sysid/site ID doesn't matter?

2. DSD reports two channels, "1" and "2'", on discrete frequencies. Can these be considered LCNs for sake of submitting to RR?

3. The frequencies involved in these channels are quite tight together: 143.115 is channel 2, and is on the owner's license, but I have found channel 1 to be 143.110 (only 5kHz down). This is not typical spacing here in Canada (I think it's 15kHz in that part of the band). I can watch the idle bursts on the spectrum display and know that I am right on the frequencies - nothing else in the band nearby or on/near other licensed freqs for this company decodes as IDAS. Is that typical of the bandwidth employed on such a system?

Thanks as always!
 

EricCottrell

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Hello,

I keep having to remember to search that band when I am up in Canada. Hydro-Quebec has a system on 142 Mhz and I usually search with 5 KHz steps. The FCC emission bandwidth is 4 Khz, so 5 KHz spacing should be doable. I have seen VHF radio specifications that mention 2.5 KHz frequency steps, so there could be 5 KHz spacing with a 2.5 KHz offset. It could be the case if 143.115 is the allocated frequency, that Channel 1 is 143.1125 and Channel 2 is 143.1175.

I am more used to UHF where 6.25 KHz spacing with a 3.125 KHz offset is used. I have seen one 12.5 KHz frequency allocation where two NXDN channels are used, one 3.125 KHz above the allocated frequency, and the other 3.125 KHz below the allocated frequency.

Think of the system as a all digital LTR system. The same repeater numbering scheme is used, so Channel 1 is Repeater 1, and Channel 2 is Repeater 2. The 2- portion of the id is the home repeater and you should see most traffic on Repeater 2.

73 Eric
 

kd7rto

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I'm trying to get my DSDPlus.frequencies file working correctly. When I try the following, I get the 153.05 and 152.36 showing up as channels 1 and 2 on all sites, not just site 2:

IDAS,0,2,1,153.05,153.05,0
IDAS,0,2,2,152.36,152.36,0

When I try this they do not show up at all:

IDAS,2,0,1,153.05,153.05,0
IDAS,2,0,2,152.36,152.36,0

Anyone have any great ideas for resolving this?
 

natedawg1604

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I'm trying to get my DSDPlus.frequencies file working correctly. When I try the following, I get the 153.05 and 152.36 showing up as channels 1 and 2 on all sites, not just site 2:

IDAS,0,2,1,153.05,153.05,0
IDAS,0,2,2,152.36,152.36,0

When I try this they do not show up at all:

IDAS,2,0,1,153.05,153.05,0
IDAS,2,0,2,152.36,152.36,0

Anyone have any great ideas for resolving this?
Just FYI, DSD+ doesn't (yet) support trunk-tracking for IDAS, you can only monitor individual frequencies. So to properly monitor IDAS systems, you have to "manually" monitor each frequency with a separate instance of DSD+. That being said, after commenting out the above-referenced frequency file entries, can you provide a screenshot of the DSD+ event log window associated with each frequency?
 
D

DaveNF2G

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This is what my file looks like for the two nearest sites of a larger system:

IDAS, 000, 12, 11, 462.16250, 467.16250, 0
IDAS, 000, 12, 12, 463.81250, 468.81250, 0
IDAS, 000, 12, 13, 452.80000, 457.80000, 0
IDAS, 000, 12, 14, 464.92500, 469.92500, 0
IDAS, 000, 12, 15, 451.98750, 456.98750, 0
IDAS, 000, 15, 11, 462.53125, 467.53125, 0
IDAS, 000, 15, 12, 451.82500, 456.82500, 0
IDAS, 000, 15, 13, 461.53750, 466.53750, 0
IDAS, 000, 15, 14, 462.13750, 467.13750, 0
IDAS, 000, 15, 15, 464.86250, 469.86250, 0
 

moj

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Re Idas system's

Hi Eric !

I've only just found this post and thankyou for the description for describing how the hex is displayed on the idas system .

If you can remember I sent you a message a while back when I was first learning about the idas that I had found but after a lot of research I can now hear the scrambled audio on the radio that beforehand I was not able to hear until you explained my step size could of been incorrect etc .

I'm based in the uk so I'm not sure if system's are different to your location but while scanning around I found the idas frequency's that are local to me which seem to be as follow's

453.097125 which is CH 2 ,
453.103125 which is CH 1 ,
453.822125 which is CH 4
453.828125 which is CH 3
456.547125 which is CH 6
456.553125 which is CH 5
according to my dsdplus window , do these frequency's sound correct to you because my source I'm using is my funcube dongle pro plus which is usually very accurate also this is the order there appearing in from first to the last on my sdr .

After seeing all the above frequency's in use what kind of idas site would you class this as and any idea how many repeater's are in use etc ?

My other question is due to the frequency's are using the digital 15 bit scrambling code and I'm guessing with the icom UT-126H card seeing as it's idas digital voice that I'm recieving I decided to buy myself a Aor-dv1 base receiver which has the feature to descramble the code on the nxdn 15 bit code's , but sadly it will not sniff the required 5 digit key on the idas system so is there a difference between idas and nxdn 15 bit scrambling setup and as you probably know the uk is more relaxed on the law's of encryption than the usa so any help I'd be really grateful .

Also on your post you can see the hex displayed on your dsd on the right hand side , how is this window enabled so I can try using your method to find out more info regarding the idas system etc ?

as always thanks in advance ;)
 

EricCottrell

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Hello,

The only way I know to check those frequencies is when listening to a multi-site system on the frequency used for registration. I do not know if DSDPlus decodes the Site Channel Information. I am not familiar with UK UHF allocations.

If the system does use the 15 bit scrambling, then the AR-DV1 can search for the code. I tried it and it works. I was also able to use the code in my Icom IC-R8600. Follow the instructions in this link.
http://www.aorja.com/udoc/AR-DV1_undocumented_features.pdf
The click of the main dial brings up the D-CR (NXDN) scramble code. The long press of the mode button starts the search.

The hex is from my version of DSD. Try the DSDPlus command line option for more verbose output. I think it is -v4.

73 Eric
 

moj

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Thanks for the reply eric , and for some strange reason the dv1 descrambler just flashes the question mark's like its not able to sniff the code in use so i have been trying to do it manually from 1 to 32'767 and as you can imagine its a very long and stressful test of the mind having to try each code one by one , also theres only 63 key's that can be entered into the icom cps .

From my research tho there only using the ut-126h due to cost price of each radio with the addon so it's really strange ?

Also the annoying thing in the uk due to idas not being really widely used like dmr its harder finding people who understand the systems working's etc

I have an idea tho are you able to send an idas scrambled cps codeplug and i'll try your's on my side with my dv1 and see if i get the same result's ?

thanks again ;)
 

EricCottrell

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Hello,

The question marks flashing means it is searching for the code. It may take awhile depending on activity. The different users on the system maybe using different codes.

73 Eric
 
D

DaveNF2G

Guest
This is what my file looks like for the two nearest sites of a larger system:

IDAS, 000, 12, 11, 462.16250, 467.16250, 0
IDAS, 000, 12, 12, 463.81250, 468.81250, 0
IDAS, 000, 12, 13, 452.80000, 457.80000, 0
IDAS, 000, 12, 14, 464.92500, 469.92500, 0
IDAS, 000, 12, 15, 451.98750, 456.98750, 0
IDAS, 000, 15, 11, 462.53125, 467.53125, 0
IDAS, 000, 15, 12, 451.82500, 456.82500, 0
IDAS, 000, 15, 13, 461.53750, 466.53750, 0
IDAS, 000, 15, 14, 462.13750, 467.13750, 0
IDAS, 000, 15, 15, 464.86250, 469.86250, 0
When that log was made, evidently the system was not fully configured.

The network number is 1366 and the Area is 1.

So a line should now look like:

IDAS, 1366, 12, 11, 462.16250, 467.16250, 0

Each site identifies as 1.1366-[site#]

DSD+ reports talkgroups in format n-nnn. So far I have seen prefixes 1 through 4.

Radio IDs are reported in the same format.

In RRDB, talkgroups are listed as 00-nnnn, which must be how Uniden scanners require them to be entered. I haven't had a chance to test this yet.
 

rspc

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Hello,
In the next version of dsd + fast lane could ICOM IDAS 6.25mhz decoder be added? it is a system that is increasingly used and it would be interesting to have it in the dsd +.
Thank you.

Hola buenas,
En proxima version de dsd+ fast lane se podria añadir ICOM IDAS 6,25mhz decoder? es un sistema que cada vez se utiliza mas y estaria interesante tenerlo en le dsd+.
Muchas gracias.
 

mtindor

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Hello,
In the next version of dsd + fast lane could ICOM IDAS 6.25mhz decoder be added? it is a system that is increasingly used and it would be interesting to have it in the dsd +.
Thank you.

Hola buenas,
En proxima version de dsd+ fast lane se podria añadir ICOM IDAS 6,25mhz decoder? es un sistema que cada vez se utiliza mas y estaria interesante tenerlo en le dsd+.
Muchas gracias.
IDAS is supported, at least in Fast Lane versions. I don't know about the "free" version. You should set bandwidth to 4.00 khz in FMP24 / FMPA, or to 4000 in SDR#. You should also use the "-fn" switch on the DSDplus commandline if you are having issues.
 

rspc

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Hello,
I use the latest version DSD + fast lane 2.155 along with HDSDR but not decoder IDAS, could you help me?
Thank you.

Hola buenas,
Yo utilizo la ultima version DSD+ fast lane 2.155 junto con HDSDR pero no decoder IDAS, me podria ayudar?
Muchas gracias.
 

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