Communication problems and successes played an important role in the September 11, 2001, attacks and their aftermath. Systems were variously destroyed or overwhelmed by loads greater than they were designed to carry, or failed to operate as intended or desired.
Most public switched telephone networks have a single emergency telephone number that allows a caller to contact local emergency services for assistance. The emergency number differs from country to country; it is typically a three-digit number so that it can be easily remembered and dialed quickly. Some countries have a different emergency number for each of the different emergency services; these often differ only by the last digit.
Terrestrial Trunked Radio, a European standard for a trunked radio system, is a professional mobile radio and two-way transceiver specification. TETRA was specifically designed for use by government agencies, emergency services, for public safety networks, rail transport staff for train radios, transport services and the military. TETRA is the European version of trunked radio, similar to Project 25.
Computer-aided dispatch (CAD), also called computer-assisted dispatch, is a method of dispatching taxicabs, couriers, field service technicians, mass transit vehicles or emergency services assisted by computer. It can either be used to send messages to the dispatchee via a mobile data terminal (MDT) and/or used to store and retrieve data. A dispatcher may announce the call details to field units over a two-way radio. Some systems communicate using a two-way radio system's selective calling features. CAD systems may send text messages with call-for-service details to alphanumeric pagers or wireless telephony text services like SMS. The central idea is that persons in a dispatch center are able to easily view and understand the status of all units being dispatched. CAD provides displays and tools so that the dispatcher has an opportunity to handle calls-for-service as efficiently as possible.
A call box or callbox is a box containing a special-purpose direct line telephone or other telecommunications device, which has been used by various industries and institutions as a way for employees or clients at a remote location to contact a central dispatch office.
Base station is – according to the International Telecommunication Union's (ITU) Radio Regulations (RR) – a "land station in the land mobile service."
The Government Radio Network (GRN) is a network of various systems in place across Australia that enable statewide trunked radio communication. The network operates through inter-linked sites for government and public services such as police, ambulance, fire, or roads authorities which require such a system to function properly. The main aim of the GRN is to consolidate all resources into one network, ensuring greater coverage and reliability than if each department had its own independent communication system. The existence of the GRN also reduces the amount of government money and resources needed to maintain communication between units of emergency and public service branches. Last, it allows effective intercommunication among these services in times of national or state emergency for coordination of wide-scale actions.
Professional mobile radio are person-to-person two-way radio voice communications systems which use portable, mobile, base station, and dispatch console radios. PMR radio systems are based on such standards as MPT-1327, TETRA, APCO 25, and DMR which are designed for dedicated use by specific organizations, or standards such as NXDN intended for general commercial use. These systems are used by police, fire, ambulance, and emergency services, and by commercial firms such as taxis and delivery services. Most systems are half-duplex, in which multiple radios share a common radio channel, and only one can transmit at a time. Transceivers are normally in receive mode, the user presses a push-to-talk button on his microphone when he wants to talk, which turns on his transmitter and turns off his receiver. They use channels in the VHF and UHF bands, giving them a limited range, usually 3 to 20 miles depending on terrain. Output power is typically limited to 4 watts. Repeaters installed on tall buildings, hills or mountain peaks are used to increase the range of systems.
A two-way radio is a radio that can both transmit and receive radio waves, unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, used for bidirectional person-to-person voice communication with other users with similar radios. Two-way radios are available in stationary, mobile, and hand-held portable models. Hand-held two-way radios are often called walkie-talkies, handie-talkies or hand-helds. Two-way radios are used by groups of geographically separated people who need to keep in continuous voice communication, such as aircraft pilots and air traffic controllers, ship captains and harbormasters, emergency services personnel like firemen, policemen, and ambulance paramedics, taxi and delivery services, soldiers and military units, fast food and warehouse employees, and radio amateurs.
Project 25 is a suite of standards for interoperable digital two-way radio products. P25 was developed by public safety professionals in North America and has gained acceptance for public safety, security, public service, and commercial applications worldwide. P25 radios are a direct replacement for analog UHF radios, but add the ability to transfer data as well as voice, allowing for more natural implementations of encryption and text messaging. P25 radios are commonly implemented by dispatch organizations, such as police, fire, ambulance and emergency rescue service, using vehicle-mounted radios combined with handheld walkie-talkie use.
A trunked radio system is a digital two-way radio system that uses a digital control channel to automatically assign frequency channels to groups of users. In a traditional half-duplex land mobile radio system a group of users with portable two-way radios communicate over a single shared radio channel, with one user at a time talking. These systems typically have access to multiple channels, up to 40 - 60, so multiple groups in the same area can communicate. In a conventional (nontrunked) system, channel selection is done manually; before use the group must decide on which channel to use, and manually switch all the radios to that channel. This is an inefficient use of scarce radio channel resources, because the user group must have exclusive use of their channel regardless of how little transmission they are doing. There is also nothing to prevent multiple groups in the same area from choosing the same channel, causing conflicts. A trunked radio system is an advanced alternative in which the channel selection process is done automatically.
Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal.
Dispatch is a procedure for assigning employees (workers) or vehicles to customers. Industries that dispatch include taxicabs, couriers, emergency services, as well as home and commercial services such as maid services, plumbing, HVAC, pest control and electricians.
Motorola Type II refers to the second generation Motorola trunked radio systems that replaced fleets and subfleets with the concept of talkgroups and individual radio IDs. There are no dependencies on fleetmaps, therefore there are no limitations on how many radio IDs can participate on a talkgroup. This allows for greater flexibility for the agency. When scanning Motorola IDs, each Type II user ID appears as an even 4- or 5-digit number without a dash.
Mobile radio or mobiles refer to wireless communications systems and devices which are based on radio frequencies(using commonly UHF or VHF frequencies), and where the path of communications is movable on either end. There are a variety of views about what constitutes mobile equipment. For US licensing purposes, mobiles may include hand-carried,, equipment. An obsolete term is radiophone.
MPT 1327 is an industry standard for trunked radio communications networks.
In a conventional, analog two-way radio system, a standard radio has noise squelch or carrier squelch, which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel, selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—individual calling and group calling. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios.
MDC, also known as Stat-Alert, MDC-1200 and MDC-600, is a Motorola two-way radio low-speed data system using audio frequency shift keying, (AFSK). MDC-600 uses a 600 baud data rate. MDC-1200 uses a 1,200 baud data rate. Systems employ either one of the two baud rates. Mark and space tones are 1,200 Hz and 1,800 Hz. The data are sent in bursts over the radio system's voice channel.
Remote controls are used any time a two-way radio base station is located away from the desk or office where communication originates. For example, a dispatch center for taxicabs may have an office downtown but have a base station on a distant mountain top. A Tone remote, also known as an EIA Tone remote, is a signaling system used to operate a two-way radio base station by some form of remote control.
Specialized Mobile Radio (SMR) may be an analog or digital trunked two-way radio system, operated by a service in the VHF, 220, UHF, 700, 800 or 900 MHz bands. Some systems with advanced features are referred to as an Enhanced Specialized Mobile Radio (ESMR). Specialized Mobile Radio is a term defined in US Federal Communications Commission (FCC) regulations. The term is of US regulatory origin but may be used in other regions to describe similar commercial systems which offer a radio communications service to businesses.