ScannerRadio
Trunking is a computerized method of allowing a large number of people/agencies to use a relatively small amount of actual frequencies. This is accomplished by a computer that controls all of the radios on the system, informing them of what frequency to operate on. Radios are programmed with specific talkgroups (channels) that the user can either listen to or talk on. The frequency for each talkgroup changes every time someone keys their radio to speak. The term “trunking” comes from the telephone industry, as the method of selecting the next available ‘circuit’ between exchanges is very similar to what happens in a ‘trunked’ radio system. A TrunkTracking scanner will listen to the system's control channel and follow frequency changes for whatever talkgroup you are listening to.A conventional scanner can monitor a trunked radio system, but it would not be able to track frequency changes. Conversations would make no sense, as you would be be only hearing parts of conversations across the entire system.
Motorola Trunking
Motorola trunking is the most popular trunking system in North America. Motorola trunking systems can be found in the VHF, UHF , 800 and 900 MHz bands (systems in the 700 Mhz band are planned for the future). There are two main types of Motorola trunked radio systems: Type I and Type II. Type I is archaic and is rarely used. Motorola trunked radio systems support both analog and digital voice transmissions.
Type I and Type II
Type I and Type II transmissions both use 16 bits to represent a talkgroup. These bits are sent out with every transmission and are interpreted by your scanner. A Type I system divides up those 16 bits into blocks, fleets, subfleets, and users. Talkgroups in Type I systems are usually displayed as FFF-SS, where FFF is a Fleet ID and SS is a subfleet ID. The trick with Type I systems is determining exactly how a particular system divides up those 16 bits. That information is represented by what’s called a “fleet map”. A Type II system divides the 16 bits differently than a Type I system. The 16 bits in a Type II system are split into 12 bits of talkgroup identifier and 4 status bits. The status bits identify special situations and are usually all zeroes.
As described above, status bits are the four bits transmitted after the talkgroup identifier. Typically, we are only concerned with the last three bits, as the first bit determines encryption. Most trunk tracking scanners after the Uniden BC-235 have a status bit function, which strips the status bits from the TG-ID. Scanner users should typically disregard status bits, as they are of no use to the user and can be confusing.
SmartZone
SmartZone is a type of wide-area Motorola Type II trunked radio network, employing several towers (acting as separate trunked radio systems) connected by a controller. All radios within the network can ‘roam’ across any tower in the network, similar to a cellular phone network. Any radio outside of their ‘home zone’ will cause whatever talkgroup it is monitoring to be simulcast on whatever tower it is closest to (A London OPP cruiser in Toronto will cause the London OPP dispatch to appear on the Toronto tower – but only if it’s radio is tuned to OPP London Dispatch). Fleetnet and the Toronto Trunked Radio system are SmartZone systems. In order to monitor SmartZone radio systems, you must program in each tower of the system into your scanner as a separate radio system. On some newer scanners such as the Uniden BC246T, you can use the Control Channel trunking feature to scan all towers without having to program each tower.
Patches
The dispatcher is able to connect (patch) two or more talkgroups together, so all patched talkgroups function as one (the dispatcher talks to both talkgroups, and all users on all talkgroups can speak to each other).
Usually low-traffic talkgroups are patched together during off-peak hours (Peel Regional Police 21 Division and Pearson Airport Division talkgroups are patched together overnight when the airport talkgroup is less busy, with a single dispatcher operating both). Sometimes talkgroups are patched together on a permanent basis. Toronto Police have several divisional talkgroups patched together, with a single dispatcher operating both. (22/23, 11/12, 51/53, 32/33, 51/53, 54/55, 13/Highway Patrol divisions are permanently patched). Dispatchers can also patch in non-trunked channels, such as the OFM channel, dispatch paging frequencies, I-TAC channels, mutual aid frequencies, etc. Helicopters are often connected to trunked radio systems via a patched simplex frequency, as transmissions from great heights are not authorized on trunked repeater inputs. Transmitting from the height of an operating helicopter enters the risk of interfering with distant systems that might be operating on the same frequencies.
Status Bit
Status bits, on a trunking scanner, typically display as the talkgroup number + a certain number. For example, talkgroup 112 with a radio in emergency will display on your scanner’s display as 114. The STATUS BIT function on your scanner (if so equipped) will strip the status bits from the talkgroup, so you’ll see 112 no matter what status bits are present
A list of status bits are:
ID+0 Normal Talkgroup
ID+1 All call (dispatcher talking to all talkgroups)
ID+2 Emergency
ID+3 Talkgroup patch initiated
ID+4 Talkgroup patch + Emergency
ID+5 MSEL + Emergency
ID+6 Not in use
ID+7 MSEL
ID+8 DES Encryption enabled
ID+9 All call + DES
ID+10 Emergency + DES
ID+11 Talkgroup patch + DES
ID+12 Talkgroup patch + Emergency + DES
ID+13 MSEL + Emergency + DES
ID+14 Not in use
ID+15 MSEL + DES
Fleetnet Trunking
Bell Fleetnet/GMCP/BMR refers to the province-wide Government of Ontario radio system that will eventually span about 80% of the province. Fleetnet is a Motorola SmartZone Type II wide-area mixed-mode trunked radio system. Fleetnet is operated by Bell Mobility Radio (a separate division of Bell Mobility cellular – their networks are NOT related)
The primary user of Fleetnet is the Ontario Provincial Police, who operate on unencrypted IMBE digital talkgroups (you need a digital scanner to monitor them). Current and/or future users of Fleetnet consist of:
- Ontario Provincial Police
- Ministry of Health (Ambulance Dispatch and Hospital Patches)
- Ministry of Natural Resources
- Ministry of Transportation
- Certain Municipal public safety agencies (the City of Guelph)
- Ministry of Corrections
LTR Trunking
Logic Trunked Radio – Developed by EF Johnson/Transcrypt, it’s a somewhat popular trunking format that doesn’t rely on a specific control channel – all channels are used for voice and data transmissions. LTR is not APCO compliant due to lack of an emergency/man down function and no RID (Radio ID) feature (no way to uniquely identify an individual radio), and therefore is not normally used for public safety agencies (there are some exceptions, though).
EDACS Trunking
EDACS (Enhanced Digital Access Communications System) is a type of trunking system developed by GE/Ericson/Tyco-MA/com respectively. Characteristics of EDACS are:
- Every time a radio transmits it is on a different frequency.
- There are typically 3 beeps after each transmission if you listen without a TrunkTracker
- All frequencies must be entered into your scanner in a specific order, called the LCN (logical Channel Numbering)
- There are three types of EDACS systems: Narrow, Wide and SCAT (Single Channel Autonomus Trunking)
- EDACS systems can be found in UHF, 800 and 900 MHz bands
- Data, such as AVL telemetry, can be transmitted along side voice transmissions
iDEN
iDEN is a trunked, digital radio system, most commonly found as the PTT/Direct Connect service of the Telus Mike and Nextel systems. Used mainly by businesses as a hassle-free and low-cost radio dispatch solution, it is used by a handful of police services as their primary radio system (Durham Regional Police, for example use radios on the Telus Mike system). iDEN cannot be monitored with a scanner. A large 900 MHz iDEN system is used by non-public safety workers at Pearson Airport.
Digital Communications
Digital radio is increasingly becoming popular among public safety agencies. Voice radio is modulated into a digital radio signal and is transmitted over the air.Radio spectrum is a natural resource that has become quite clogged as it's so popular. As such, narrowband requirements have been introduced into the commercial spectrum to make more room for others users. Digital radio allows more efficient use of bandwidth of the spectrum. Not to mention, digital radio sounds excellent to the end-users and uses very little bandwidth in comparison to analog to do so.
It is comprised of 2 parts:
- Over the air protocol (i.e. how to shuffle the chunks of digital “voice”)
- The CODEC which is the actual the format of the digitized voice
Motorola currently has two types of digital radio formats: VSELP and IMBE. VSELP is a first generation codec, and is seldom used these days (Peel Regional Police use VSELP for their “encrypted” channels). IMBE is P25 compliant, and is the format that the OPP use on Fleetnet. VSELP is not P25 compliant, and cannot be monitored with a digital scanner.
DIGITAL can be a used on either a single channel (i.e. Niagara Regional Police) or in a trunked system (i.e OPP in southern Ontario). Digital is not Encryption (see below); it is a type of modulation.
All digital scanners are P25 compliant, and can only receive P25 digital transmissions.
Encrypted Communications
Encrypted transmissions, unfortunately, are becoming more popular as privacy and security concerns are entering the forefront. Encryption can range from simple voice inversion (making voices on the system sound like Donald Duck) to more sophisticated encryption algorithms employing encryption keys.
Digital encryption schemes have been around for many years. Motorola’s Securenet system consists of five unique (and non-compatible) protocols: DVP, DVP-XL, DES, DES-XL and DVI-XL.
DVP/DVP-XL: Digital Voice Privacy was developed in the 1970’s by Motorola as a proprietary encryption protocol, meant mainly for non-sensitive non-classified users who wanted to eliminate eavesdropping. DVP-XL was developed to address concerns of decreased range when encryption was in use. 2.36x1021 encryption keys are possible with DVP.
DES/DES-XL: Data Encryption Standard was developed in the mid 1970’s a strictly government-only encryption protocol, used as a common standard among US Government agencies for sensitive (but not classified) communications. DES uses 7.2x 1016 possible encryption key combinations. A P25 compliant digital encoding standard is DES-OFB.
DVI-XL: This format is an export-version of DES.
For top secret communications (such as U.S. Secret Service and Homeland Security operations), an encryption key known as FASCINATOR is used. Details of the FASCINATOR algorithm is highly classified.
Monitoring of voice inversion is easy with the correct equipment. Monitoring of digital encryption is impossible, as it not only requires a radio with the proper encryption module, but it needs to be loaded with the proper key.
Aknowledgements
I would like to thank the boys and girls from ScanOnt list and the creators and contributors of the ScanOnt FAQ. The ScanOnt FAQ is the only document that explained the trunking system so easily.
The ScanOnt FAQ has been designed as a constantly evolving document. If you have any additions, suggestions or corrections, please send them to This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Scanont is Ontario's first and best Scanner resource and mailing list, and they want to make sure that ScanOnt FAQ, is the best FAQ available to it's members.
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