An electrical signal that varies constantly in voltage, unlike a digital signal which varies between two constant values (typically denoted as 0 and 1). The value of the analog signal varies all the time during transmission, whereas a digital signal changes only between two set values without intermediate variations.
Asymmetrical Digital Subscriber Line (ADSL)
ADSL refers to a pair of modems connected by a copper line that yields asymmetrical transmission of data.
Asynchronous Transfer Mode (ATM)
A way of transmission where a start signal precedes individual characters and one or more stop signals follow it. Due to this start/stop system, delays may occur between characters. Also denotes the complete system of protocols and equipment associated with cell-based communications networks. These networks have the ability to transmit voice, data, and video traffic simultaneously using a statistical multiplexing scheme. This type of switching is expected to bridge the gap between packet and circuit switching. ATM uses packets referred to as cells that are designed to switch cells so rapidly that there is no perceptible delay.
Two-way electronic voice communication between two or more people at separate locations.
The high-traffic density connectivity portion of any communications network. In packet-switched networks, a primary forward-direction path traced sequentially through two or more major relay or switching stations. Note: In packet-switched networks, a backbone consists primarily of switches and interswitch trunks.
Measures the ability of a communications channel to carry information. The capacity of information increases relative to a higher megahertz (cycles per second) in an analog transmission, and in megabits/second (Mbps) for digital transmission.
Basic Rate Interface (BRI)
An ITU-T Integrated Services Digital Network (ISDN) multipurpose user interface standard that denotes the capability of simultaneous voice and data services provided over two clear 64 kilobits/second (Kbps) channels and one clear 16 kbps channel (2B+D) access arrangement to each user location.
Binary digit, the smallest possible unit of information making up a character or a word in digital code processed by computers.
Device connecting two separate networks at the OSI Data Link Layer (Level Two Media Access Control Layer). Once bridging is accomplished, the bridge makes interconnected LANs look like a single LAN, passing data between the networks and filtering local traffic. There are two key classifications of bridge: those supporting Spanning Tree and, for Token Ring networks, those supporting Source Routing. Bridges connect networks using dissimilar protocols and do not interpret the data they carry. They control network traffic and security, filtering where necessary to boost network, performance and contain sensitive data to particular LAN areas.
A general term for a telecommunications medium of sufficient capacity to transmit high quality voice, data, and video transmissions. Broadband has been defined in many ways; e.g., a Wide Area Network (WAN) providing bandwidth greater than 45 Megbits/sec (T3); voice, data, and/or video communications at rates greater than 1.544 Megabits/sec (T-1), but has been Federally defined as data transmission each way, of 200 kilobits/second or more.
A group of optical fibers or electrical conductors, such as wires and coaxial cables, usually in a single jacket. Note: Multiple bundles of optical fibers or electrical conductors may be placed in the same cable.
A string or cluster of eight bits to represent a character.
An assembly of one or more insulated conductors, or optical fibers, or a combination of both, within an enveloping jacket. Note 1: A cable is constructed so that the conductors or fibers may be used singly or in groups. Note 2: Certain types of communications cables, especially long submarine cables but also terrestrial cables, whether the communications media are metallic or optical fiber, may contain metallic conductors that supply power to repeaters (amplifiers).
In CATV systems, a bidirectional high-speed digital communications interface located on a subscriber's or user's premises and used, for example, for Internet access or other digital communications.
Cable television (CATV)
A transmission system that distributes broadcast television signals and other services by means of a coaxial cable.
A "code/decode" electrical device that converts an analog electrical signal into a digital form for transmission purposes and then converts it back at the other end.
A permanent telephone line reserved exclusively for one patient, accessible during all hours of the day. These lines usually offer better quality than standard telephone lines, but may not significantly augment the performance of data communications. May also be known as "leased," or "private" lines.
Defense Data Network (DDN)
Used generally to refer to Milnet, Arpanet and the TCP/IP protocols those networks use. More specifically refers to Milnet and associated parts of the connected Internet that link military installations.
Dental Health Professional(s) Shortage Area (Dental HPSA)
An area is so designated if the following three criteria are met: 1. The area is a rational area for the delivery of dental services. 2. One of the following conditions prevails in the area:(a) The area has a population to full-time-equivalent dentist ratio of at least 5,000:1, or(b) The area has a population to full-time-equivalent dentist ratio of less than 5,000:1 but greater than 4,000:1 and has unusually high needs for dental services or insufficient capacity of existing dental providers. 3. Dental professionals in contiguous areas are over-utilized, excessively distant, or inaccessible to the population of the area under consideration
Digital Subscriber Line (DSL)
In Integrated Services Digital Networks (ISDN), equipment that provides full-duplex service on a single twisted metallic pair at a rate sufficient to support ISDN basic access and additional framing, timing recovery, and operational functions. Note: The physical termination of the DSL at the network end is the line termination; the physical termination at the customer end is the network termination.
Digital telecommunications channels (DS)
These channels are capable of transmitting high volume voice, data or compressed video signals. DS1 and DS3 are also known as T1 and T3 carriers. Transmission rates are 64 Kbps for DS0, 1.544 Mbps for DS1, and 45 Mbps for DS3.
A device that converts an analog signal into a digital representation of the analog signal. A digitizer usually samples the analog signal at a constant sampling rate and encodes each sample into a numeric representation of the amplitude value of the sample.
Direct Digital Imaging
Involves the capture of digital images so that they can be electronically transmitted.
A digital carrier capable of transmitting 1.544 Mbps of electronic information; the general term for a digital carrier available for high-value voice, data, or compressed video traffic.
A carrier of 45 Mbps bandwidth. One DS3 channel can carry 28 DS1 channels.
A transmission system allowing data to be transmitted in both directions simultaneously.
A system of encoding data on a Web page or email where the information can only be retrieved and decoded by the person or computer system authorized to access it. Often used on the web to protect financial data.
A communications protocol that utilizes various types of cable at a rate of 10 Mbps.
Hair-thin, flexible glass rods encased in cables that use light to transmit audio, video, and data signals.
A device that allows scanning of existing static images so that the images can be stored, manipulated, or transmitted in digital form.
A portion of the 1.544 Mbps (T1-aggregate) bit stream; the available fractions being determined by the type of multiplexer used to achieve the T1 aggregate bit stream.
Created to improve the rate of data transfer compared to previous transmission protocols, frame relay is a streamlined process of sending and acknowledging transmitted packets of data.
A communication channel over which both transmission and reception are possible at the same time.
Gigabits per second (Gbps)
A measure of bandwidth and rate of data flow in digital transmission.
Health Professional(s) Shortage Area (HPSA)
Means any of the following which the Secretary determines has a shortage of health professional(s): (1) An urban or rural area (which need not conform to the geographic boundaries of a political subdivision and which is a rational area for the delivery of health services); (2) a population group; or (3) a public or nonprofit private medical facility
A communication channel over which both transmission and reception are possible, but only in one direction at a time.
The ISDN packet switched channel on Basic Rate Interface, designed to carry user information streams at different speeds, depending on type: H11=1536Kbit/s, H0=384Kbit/s and H12= 1920Kbit/s.
A measure of radio frequency. One Hz = one cycle per second.
High frequency (HF)
Frequencies from 3 MHz to 30 MHz.
Use of algorithms to modify data representing an image, usually to improve diagnostic interpretation.
The deployment of systems that collect, organize, and report health data to improve the quality and cost-effectiveness of health care, public health, and providers and consumers decision-making about health care management (e.g., electronic medical record, integrated health care management systems, disease tracking systems).
Integrated Services Digital Network (ISDN)
A completely digital telephone system that is slowly enjoying more popularity throughout the United States which permits the integrated transmission of voice, video, and data to users at a higher speed than would be possible over typical telephone lines. It also provides connections to a universal network. It currently requires special installation and equipment.
A group of networks that are interconnected so that they appear to be one continuous network, and can be addressed seamlessly at the Network Layer Three of the OSI model. Typical internets are built using routers, either to form a backbone network comprised of routers, or to link together LANs at the Network Layer.
A collection of networks and gateways, including the Milnet and NSFNET, all using the TCP/IP protocol suite. It functions as a single, cooperative virtual network. The Internet provides universal connectivity and three levels of network services: connectionless packet delivery; full duplex stream delivery, and application level services, including electronic mail and EDI.
Internet Protocol (IP)
The messenger protocol of the TCP/IP (Transmission Control Protocol/Internet Protocol), describing software that tracks the Internet address of nodes, routes outgoing messages, and recognizes incoming messages. It facilitates the identification of the Internet Protocol Address (IP Address) of a computer or other device on the Internet (normally printed in dotted decimal form, such as 220.127.116.11).
The condition achieved among communications and electronics systems or equipment when information or services can be exchanged directly between them, their users, or both.
1,000 = 103
Kilobits per second (Kbps)
A measure of bandwidth and rate of data flow in digital transmission. One Kbps is 1,024 kilobits per second.
Local Area Network (LAN)
A network of computers, generally small in number, whose reach is limited, typically within a building or campus, linked to allow access and sharing of data and computer resources by users. Differentiated from MAN and WAN by the size of the area, LAN is the smallest.
Medically Underserved Areas (MUA)
May be a whole county or a group of contiguous counties, a group of county or civil divisions or a group of urban census tracts in which residents have a shortage of personal health services.
Megabits per second (Mbps)
A measure of bandwidth and rate of data flow in digital transmission. One Mbps is equivalent to one million bits per second.
Mental Health Professional(s) Shortage Area (MHPSA)
An area is so designated if the following criteria are met:
The area is a rational area for delivery of mental health services;
One of the following conditions exists within the area:
The area has unusually high needs for mental health services, and has:
An area will be considered to have unusually high needs for mental health services if one of the following criteria is met:
Metropolitan Area Network (MAN)
A network of computers whose reach extends to a metropolitan area. MANs may be used to link telemedicine applications at a data rate similar to DS1. In some cases, MANs may be used by cable companies to offer links to off-network services such as the Internet, airline reservation systems, and commercial information services, in addition to data exchange abilities. Compared to LAN and WAN, MAN is in between the two.
A measure of computer storage and memory capacity. One Mb is equivalent to 1.024 million bytes, 1,024 thousand bytes, or 1.024 Kbs. However, this term is also applied to the more rounded term of 1 million bytes.
A measure of bandwidth and rate of information flow for analog transmission. One Mhz equals 10 to the sixth power cycles per second.
Loosely, an electromagnetic wave having a wavelength from 300 mm to 10 mm (1 GHz to 30 GHz). Note: Microwaves exhibit many of the properties usually associated with waves in the optical regime, e.g., they are easily concentrated into a beam.
AA device that translates digital signals to pulse tone (analog) signals to enable transmission over telephone lines and reconverts them to digital form at the point of reception, thus permitting a computer to communicate with another computer over a regular telephone line. These devices are usually identified by the speed (in bits per second, or bps) of communication they permit. The higher the bps, the faster the modem.
Multipoint Control Unit (MCU)
A multiport device, by means of which two or more audiovisual terminals may intercommunicate in a conference call. Note: A "principal MCU" has been assigned a superior controlling function in a call where two or more MCUs in that call are termed "satellite MCUs". The physical realization of an MCU may be such that two or more independent conferences may be set up within the same unit; logically, however, there is no relationship between these conferences; the text of this definition refers to an MCU only as a logical entity pertinent to the particular call of concern.
A set of nodes, points or locations which are connected via data, voice, and video communications for the purpose of exchanging information. Interconnected telecommunications equipment used for data and information exchange. Consists of different types, LAN, MAN, and, WAN being examples.
Open Systems Architecture
A design that permits the interconnection of system elements provided by many vendors. The system elements must conform to interface standards.
Optical Carrier (OC)
The nomenclature for the line rate of the optical transmission signal.
Optical Ring (Disk)
A computer storage disk used solely for large quantities (Gbs) of data.
Any device that is attached to a computer externally. Scanners, mouse pointers, printers, keyboards, and monitors are all examples of peripherals. Scales, blood pressure cuffs, spyrometers, and glucometers are also examples.
Picture Archiving and Communications System (PACS)
A system capable of acquiring, transmitting, storing, retrieving, and displaying digital images and relevant patient data from various imaging sources, and communicating the information over a network.
The type of computer on which a given operating system or application runs; the operating system in use on a given computer; or the application program in use on a given computer and operating system. The term cross-platform may be used to characterize an application program or operating system that may be run on more than one platform.
Primary Rate Interface (PRI)
An integrated services digital network (ISDN) interface standard that is designated in North America as having a 23B+D channels, in which all circuit-switched B channels operate at 64 kb/s, and in which the D channel also operates at 64 kb/s. Note: The PRI combination of channels results in a digital signal 1 (T1) interface at the network boundary.
In networking, to send data from a server to a client in compliance with a previous request from (via) the client, as soon as the data are available.
The capture, processing, and presentation of data, audio, and/or video signals at the time the data is originated on one end and received at the other end. When signals are received at rates of 30 frames per second, real time is achieved.
Redundant or Redundancy
Known as fault-tolerance, in data transmission, refers to characters and bits that can be removed from a transmission without affecting the message. In data processing and data communications, it means providing backup for components: should one of them fail, the system continues to run without operation. Total redundancy is usually impractical, but organizations with mission-critical applications attempt to install a high level of redundancy on the basis that downtime loses money, or possibly lives, depending on the business.
In data communications, a functional unit used to interconnect two or more networks. Routers operate at the network layer (layer 3) of the ISO Open Systems Interconnection Reference Model. The router reads the network layer address of all packets transmitted by a network, and forwards only those addressed to another network.
An electronic retransmission instrument serving as a repeater, which is a bi-directional device used to amplify or regenerate signals, placed in orbit around the earth in geostationary orbit for the purpose of receiving and retransmitting electromagnetic signals. It typically receives signals from a single source and retransmits them over a wide geographic area, known as the satellite's "footprint."
A network device that provides service to the network users by managing shared resources. The term is often used in the context of a client-server architecture for a local area network (LAN).
Slow scan video
A device that transmits and receives still video pictures over a narrow telecommunications channel.
Transmission of static images or audio-video clips to a remote data storage device, from which they can be retrieved by a medical practitioner for review and consultation at any time, obviating the need for the simultaneous availability of the consulting parties and reducing transmission costs due to low bandwidth requirements.
A technique for transferring data (usually over the Internet) in a continuous flow to allow large multimedia files to be viewed before the entire file has been downloaded to a client's computer.
In communications systems, a mechanical, electro-mechanical, or electronic device for making, breaking, or changing the connections in or among circuits. Also known as the process by which one transfers a connection from one circuit to another. In a computer program, a conditional instruction and a flag that is interrogated by the instruction or a parameter that controls branching and that is bound, prior to the branch point being reached.
The process by which bits are transmitted at a fixed rate with the transmitter and receiver synchronized, eliminating the need for start/stop elements, thus providing greater efficiency.
A type of telephone line service offering high-speed data or voice access, with a transmission rate of 1.544 Mbps. It is also known as D1.
A digital transmission system for high volume voice, data, or compressed video traffic, with a transmission rate of 44.736 Mbps. It is also known as D3.
The use of wire, radio, visual, or other electromagnetic channels to transmit or receive signals for voice, data, and video communications.
Interactive electronic communication between multiple users at two or more sites which facilitates voice, video, and/or data transmission systems: audio, audiographics, computer, and video systems.
The physical separation between multiple providers during a consultation.
The detection of a disease as a result of evaluating data transmitted to a receiving station from instruments monitoring a remote patient.
The use of electronic information and telecommunications technologies to support and promote long-distance clinical health care, patient and professional health-related education, public health, and health administration.
The use of information processing based on a computer in telecommunications, and the use of telecommunications to permit computers to transfer programs and data to one another.
The use of electronic communication and information technologies to provide or support clinical care at a distance. Included in this definition are patient counseling, case management, and supervision/preceptorship of rural medical residents and health professions students when such supervising/precepting involves direct patient care.
The use of audio, video, and other telecommunications and electronic information processing technologies to provide individual guidance or direction. An example of this help may involve a consultant aiding a distant clinician in a new medical procedure.
The process of using audio, video, and other telecommunications and electronic information processing technologies to monitor the health status of a patient from a distance.
The method of using robotic and other instruments that permit a clinician to perform a procedure at a remote location, by manipulating devices and receiving feedback or sensory information, that contributes to a sense of being present at the remote site and allows a satisfactory degree of technical achievement. For example, this term could be applied to a surgeon using lasers or dental handpieces and receiving pressure similar to that created by touching a patient so that it seems as though s/he is actually present, permitting a satisfactory degree of dexterity.
Transmission Control Protocol/Internet Protocol (TCP/IP)
The underlying communications rules and procedures that allow computers to interact with each other on the Internet.
The speed at which information passes over a communications channel, generally given in either bits per second (bps) or baud.
Actual-time, generally two way transmission of digitized video images between multiple locations; uses telecommunications to bring people at physically remote locations together for meetings. Each individual location in a videoconferencing system requires a room equipped to send and receive video.
A telephone that is coupled to an imaging device that enables the call receiver or the call originator, or both, to view one another as on television, if they so desire; a military communications terminal that has video teleconference capability, is usually configured as a small desktop unit, designed for one operator, and is a single, integrated unit.
Video teleconference (ing) (VTC)
A teleconference that includes video communications, specifically pertaining to a two-way electronic communications system that permits two or more persons in different locations to engage in the equivalent of face-to-face audio and video communications. Note: Video teleconferences may be conducted as if all of the participants were in the same room.
Virtual Private Network (VPN)
The provision of private voice and data networking from the public switched network through advanced public switches. The network connection appears to the user as an end-to-end, nailed-up circuit without actually involving a permanent physical connection, as in the case of a leased line. VPNs retain the advantages of private networks but add benefits like capacity on demand.
Virtual Local Area Network (VLAN)
A computer network using inter-networks as data links that are transparent for users and that do not have restrictions on protocols, so that the network has the characteristics of a local area network.
A computer-based technology for simulating visual, auditory, and other sensory aspects of complex environments to create an illusion of being a three-dimensional world. The world is designed by the computer and viewed through a special headset that responds to head movements while a glove responds to hand movements. For example, while in a virtual room a person may move their hand up in order to fly or tap to change the color of a wall.
Wide Area-Network (WAN)
Data communication networks that links together distant networks and their computers to provide long-haul connectivity between separate networks located in different geographic areas.
Descriptive of a network or terminal that uses electromagnetic waves (including rf, infrared, laser, visible light-and acoustic energy) rather than wire conductors for telecommunications.
World-Wide Web (WWW)
The universe of accessible information, including graphics, sound, text and video accessible through the Internet. The Web has a body of software, a set of protocols and defined conventions for accessing such information, including HTML (HyperText Markup Language), the Web's software language, and TCP/IP, a family of networking protocols providing communication across interconnected networks.
ADSL Asymmetrical Digital Subscriber Line
ATM Asynchronous Transfer Mode
BRI Basic Rate Interface
CATV Cable television
Dental HPSA Dental Health Professional(s) Shortage Area
DSL Digital Subscriber Line
DDN Defense Data Network
DS Digital telecommunications channels
Gbps Gigabits per second
HF High frequency
HPSA Health Professional(s) Shortage Area
IP Internet Protocol
ISDN Integrated Services Digital Network
Kbps Kilobits per second
LAN Local Area Network
MAN Metropolitan Area Network
Mbps Megabits per second
MCU Multipoint control unit
MHPSA Mental Health Professional(s) Shortage Area
MUA Medically Underserved Areas
OC Optical Carrier
PACS Picture Archiving and Communications System
POTS Plain Old Telephone Service
PRI Primary Rate Interface
TCP/IP Transmission Control Protocol/Internet Protocol
VLAN Virtual local area network
VPN Virtual Private Network
VTC Video teleconference (ing)
WAN Wide Area Network
WWW World Wide Web
Universal Service for Rural Health Care Providers Federal Communications Commission
Distance Learning & Telemedicine Program U.S. Department of Agriculture