The differences between Privacy Plus, SmartNet, SmartZone, SmartZone OmniLink, and networks in general

My knowledge of the early history of Motorola trunking isn't terrific but I believe the first systems were marketed as Privacy Plus. This was meant to mean that now two-way radio users had their own specific channels, or fleets, and made there conversations private from everyone else on the network. With conventional radio and community repeaters you simply could go into monitor mode and hear all other traffic on the network compromising privacy. The system was not necessarily secure or meant to be, but now conversations were private. You didn't have to contend with the talkative taxi company or the foul mouthed truck drivers. When you wanted to talk you picked up the microphone and talked, this is permitting someone else on your sub-fleet wasn't talking. Privacy Plus didn't really add advanced features other than basic trunking. Later enhancements were developed such as Privacy Plus-enhanced, Privacy Plus-SE, ShareNet, and Coverage Plus. These networks were more geared toward the SMR operator.

Considering Privacy Plus was one of the first networks and Type I was the first protocol to be used a majority of Privacy Plus systems were Type I. As Type II evolved it was added to the capabilities of Privacy Plus but never truly became widespread. Type I radios were simple to use and cheap.

Later, another the entry level trunking solution was introduced called StartSite. StartSite offered basic trunking, telephone interconnect, and a maximum of 5 channels. This was great for a large office, warehouse, or shipyard.

With the creation of the APCO-16 standard Motorola now needed to add support to their systems in order to be compliant with the standard. The standard was strictly aimed toward Public Safety. Motorola's answer was SmartNet. It added the features of PTT-ID, prioritizing radio ids and talkgroups, dynamic regrouping, emergency alarm/call, automatic channel assignment/updating, busy queuing/call back, selective radio inhibit, subscriber access control (SAC), digital voice encryption, redundancy of AMSS remote sites, telephone interconnect, and SMR backup/roaming. Here are the details of the most used features below.

PTT-ID: Every call would require the radio id to be sent to the system for authorization. That way all radios on the network were always properly identified.
Assignable priority levels: There are a total of 8 priority levels though only 7 are assignable. The highest priority is reserved for emergencies. This feature allowed priority access to the system for Public Safety over say, trash collection or a school district.
Dynamic Regrouping: Dynamic regrouping allows a Dispatcher or trunked terminal to send a dynamically assigned talkgroup to a radio. A specific mode is programmed for Dynamic Regrouping. In the event of an emergency where a talkgroup is created ad hoc for the incident, the talkgroup can be sent to the radio so that all radios would have access to this talkgroup. The use of the feature is endless.
Emergency alarm/call: In the event of an emergency the subscriber could push a button on their radio, alert the dispatcher, and have highest priority access to the system. There are two ways for this to work when the system is full. One of them is called ruthless preemption, which will interrupt the lowest priority user and gives the higher priority emergency access to the channel. The lower priority subscriber is basically bumped off the system. The other alternative is to queue the emergency yet put it at the top most level of the queue if other subscribers have been queued.
Channel assignment/updating: When a call is placed it will be reflected over the control channel and a continuous message will be sent out informing late entry subscribers of the call in progress.
Busy queuing/call back: If all channels within the system are in use a queue is created for any subscriber which is unable to place a call. Once they are given access to the system, they are called back. This is typically announced by the radio emitting the talk-permit tone.
Selective radio inhibit: If a radio is lost or stolen it can be sent a command which places it into a dormant state. The radio will operate as normal but will give no sign to the subscriber it is operating or allow the subscriber any access to the radio whatsoever. The radio basically becomes dead, though not deaf to the system it was inhibited on. That way the radio can be restored (Xinhibited) by a Dispatcher or trunked terminal.
Subscriber Access Control: This is a database which is commonly referred to as the SAC. It is a database of radios and talkgroups which are allowed to access the system, or are not allowed to access the system. Earlier versions of the SAC database had two options; the first was to allow all access to the system except for specific radios or groups, and the second was to only permit groups and radios which were entered into the database. Newer SAC databases, used by SmartZone for example, allow radio ids and talk groups to be created and then individually enabled or disabled on an as-needed basis.
Digital voice encryption: All or specific transmissions on the network can be encrypted or sent in the clear. Radios to be encrypted are loaded with a key (As DES requires a key to operate) and then can select whether they want to transmit in the clear or coded. Specific groups, or activities can be slaved for coded or clear. Often, encryption is referred to as coded communications.
Telephone interconnect: Subscriber radios, which when properly programmed, may initiate a half-duplex phone call. A button is pressed on the radio and a dial tone will appear. That is unless the feature has been disabled or allotted time has been exceeded.

Motorola's answer for APCO-16 support was the marketing name SmartNet. SmartNet was first introduced when Type I was the only protocol available. SmartNet was then referred to as SmartNet I. When Type II was introduced SmartNet II was created. Later on an improved version was created called SmartNet II+. I do not have any details as to the specific differences or if there was really an improvement. Typically you can never tell the difference between II and II+.

With the need for Wide Area Coverage Simulcast was introduced permitting multiple trunked sites within a network. As the same as conventional simulcast, one site is the prime site (Containing the voting comparator) and the rest are remote sites. The prime site contains the primary site controller with each remote site having a remote site controller (ReSC). Currently you are limited to 10 sites in a trunked Simulcast network. With Simulcast all sites use the same frequencies, because of this, all sites must have one form of synchronization, which is predominately done with GPS these days, but a clock sync can still be sent along a leased line.

In addition, a trunked network can use Receiver Voting, which is basically half of what Simulcast does. There are multiple sites strictly for receiving which send the audio to the prime site which then compares them and then votes which is the best source. That audio path is then sent to the transmitter sites. Sites can typically have both transmitters and receivers but there will still be a few which will be strictly for receive only.

Motorola uses three types of voting systems for Simulcast and Receiver Voting. The first and oldest is SpectraTAC. [The TAC stands for Total Area Coverage.] Next in line was DigiTAC. DigiTAC added the support for voting of 12kbit encryption and data. The last, and current, is ASTROTAC, which performs all the previous forms of voice and data plus ASTRO modulation. All these systems are used on both conventional and trunked networks. In some cases if you pay attention to the sound at the end of the transmission you'll hear a pop-click type sound which varies per TAC type but can be used to determine what type of voter is being used.

SmartNet systems in the beginning were limited to a maximum of 21 channels per network. Later the hardware was modified for a maximum of 28, which is still the current maximum. But say a customer didn't need such large capabilities such as 28 channels or 60,000 radio ids? They wanted something smaller and they were given SmartWorks. SmartWorks gave the customer full APCO-16 support but gave them a smaller database and a limited amount of channels (8). At a later date the customer could upgrade to a SmartNet II network if needed. I believe the University of California supplies all its campuses with SmartWorks networks.

An alternative to Simulcast technology when Wide Area Coverage is needed is AMSS. AMSS stands for automatic multiple site selection. Each individual site in the network is not restricted by frequency or number of channels. One site can have 20 channels, one can have 4, and another can have 12. The restriction here is that each site has different frequencies.

Each site in an AMSS network will have an individual site number assigned to it and has it broadcasted over the control channel. When a subscriber is granted a call at one site his or her talkgroup will be broadcasted at every site on the first available channel. In certain configurations the call may not be permitted if a site has all channels in use.

AMSS added flexibility but did not truly give the network efficiency for assignment of resources. Today there are a small few of AMSS networks in use. I can recall one in Texas operated by the Military and one in the San Francisco Bay Area operated by the Department of the Interior for the Golden Gate National Park. Each one operates on UHF.

Enter SmartZone. SmartZone allows multiple trunked networks, be they single or multiple site, to be interconnected and communicate in a wide-area fashion. Besides being interconnected they are all controlled by a master controller called the Zone Controller (ZC). The ZC has the master database and is the primary point for control of audio paths within the network. Though each individual site has a controller it basically goes into a passive mode while connected to the ZC. The ZC chassis permits a total of 64 connections via RS-232. Below I've listed possible equipment which can take up a port on the ZC.

Trunked site: This is basically a communications path to the site controller. It can either be a 6809 site or an IntelliRepeater.
CIU Distribution Panel Link (CDL): Console Interface Units (CIU) connect through here. A CIU is responsible for encryption and decryption of traffic for a recording device or dispatcher console.
Data Broadcast Link (DBL): Digital Interface Units (DIU) connect through here. A DIU is similar to a CIU yet it is for demodulating ASTRO traffic.
Business Exchange: The Business Exchange is responsible for handling telephone interconnect.

As you can see the ZC supports a total of 64 sites per zone network, but that is if telephone interconnect and/or consoles are not used. A majority of agencies or organizations in charge of a SmartZone network will have consoles so the number of sites will be reduced.

Another important part of a SmartZone network is the Ambassador Electronics Bank (AEB). The AEB's primary responsibility is to switch audio. It takes audio paths from an input source and then, based on the ZC's decision, routes them to specific output ports. Every channel, or station, within the zone network is connected to the AEB.

Why is this important? SmartZone systems use what is called Dynamic Site Assignment for efficient allocation of resources. DSA is a feature which AMSS didn't have. An AMSS network could not control which sites broadcasted which talkgroups. The feature of DSA is it assigns only the sites which need to the audio for an affiliated subscriber. For example, we have a SmartZone network with 5 sites. One of these sites is our main traffic site with a majority of our subscribers affiliated to this site, the other four sites are strictly for fill-in. Once a subscriber leaves the main site he or she will affiliate at one of our fill-in sites. Lets say this subscriber is on "Metro Dispatch." The affiliation to Metro Dispatch is sent to the ZC which in turn updates its table as to which sites get Metro Dispatch broadcasted to it. The ZC when then tell the AEB to create an audio path between our main site and that specific fill-in site. Before this subscriber roamed to this site there was no one there affiliated to Metro Dispatch. Metro may have been really busy at our main site but there was no traffic whatsoever at our fill-in site. This is why affiliations are important in a SmartZone network.

Another important feature of SmartZone is an added level of redundancy. If a normal trunked system has a fault occur with the central controller it would go into Failsoft. With SmartZone there is one level added in-between. This is called Site Trunking. When a SmartZone network is operating normally it is referred to as Wide Area trunking. If a site somehow loses its link to the ZC it will revert to Site Trunking. In this mode the site continues to operate normally but without rebroadcast of audio to other sites. Being we lost our link we can't pass the audio. With a 6809 controller you can have a local backup SAC database but in most cases this isn't done. We don't want sites to go into Site Trunking. Now if the individual site has a problem with its controller the site will go into Failsoft. Even though the site is connected to the ZC with it in control, the ZC tells the local site controller what to do.

Considering SmartZone systems are highly configurable they permit the administrator the option to restrict radios or talkgroups to specific sites. If you setup a site strictly for the northern part of the county and have talkgroups for that specific area you can restrict them to that site. In addition if you have a subscriber who only needs coverage for one or two sites you can select which sites they can use. If the radio tries to affiliate to another site, which it received from an adjacent site announcement, it will receive a rejection and leave the site. Since we use affiliations for basic control on the network, the transition is quick and painless.

One piece of equipment strictly for use on a SmartZone network is the IntelliRepeater (IR). An IR site does not need a separate controller. Each station at the site is an IR and can perform the function of a control channel if needed.

What happens when we need more than 64 sites? Motorola created an enhancement to SmartZone called OmniLink. OmniLink is basically software driven and is primarily interconnection and communication between different SmartZone networks. Each SmartZone network in an OmniLink network is called a Zone. Basically each SmartZone network is identified by a system id for every site. So each Zone in an OmniLink network would have a different system id. You're then allowed up to three zones, or a total of 192 sites.

Being there's not a lot more to OmniLink there isn't much more to say. Each Zone in the OmniLink network still has its own ZC, with its own database, but each ZC is now interconnected. When a radio roams to another Zone it first must get permission to trespass into this new Zone. This radio found out about this other Zone through the adjacent site announcement. Sites can actually be configured to not allow trespass and will indicate so in the site background word.

SmartZone systems have a million and one different ways to be configured and support a wide variety of features. These are best left for another discussion. I may further include more information at a later time. If you feel I missed something please email me and let me know.

05/12/2007

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