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SEE Common Carrier.

Case-Based Reasoning (CBR)
A physician, diagnosing the illness of a new patient, is reminded of a past patient and checks a computerized database to see if the former diagnosis is relevant. This is an example of Case-Based Reasoning (CBR), a form of problem solving in which the problem solver reuses a past case to solve a new problem. The CBR-MED mailing list provides a forum for the discussion of CBR methods in Medicine. The list brings together medical practitioners, health informaticians, and CBR researchers to spur the development of CBR methods

Camera control
May be near end (local control of local pan/ tilt/ zoom/ iris/ focus) or far end (local control of p-t-z at the remote site). May be quite useful in consultations if the examiner wants to control the remote camera's view without having to provide verbal directions to the assistant at the remote site.

Center for Advanced Medical Informatics at Stanford (CAMIS)

A radio frequency assignment made according to the frequency band being used and the geographic location of the send/receive sites. A communication path established between two or more institutions.

Channel Service Unit / Data Service Unit (CSU/DSU)
A hardware device that is needed to terminate a high speed telecommunications connection. It is inserted between the telemedicine system (i.e., CODEC) and the communications line. It conditions and strengthens the signal, and supports the necessary link protocols, for transmission of data from LANs, video systems, and other applications over leased or switched communications lines (T1, fractional T1, leased or switched 56, ISDN). Some models allow the allocation and sharing of bandwidth with other traffic, such as digitized voice from a PBX, and act as a multiplexer.

Charge coupled device (CCD)
Charge coupled device = "chip". A 1-CCD ("1-chip") camera contains a single charge coupled device with specialized semiconductors. These contain photosensitive cells that generate voltage when struck by photons of light. One photosensitive cell equates to one pixel in the displayed image. The number of cells on a chip determines the number of pixels of resolution the camera can display. The larger the chip the greater the image resolution. Increased resolution is accomplished either by using larger chips or by using more of them. Single chip cameras do a good job. 2-CCD cameras use one chip for chrominance and one for luminence. Three chip cameras do an even better job because they have more total cells and because they use one chip each to capture red, green and blue light. Three chip cameras provide images with higher resolution and better color representation, and can cost 10 times as much as 1-CCD cameras. A 1-CCD camera can support 640 pixels x 480 lines and 24 bit color. A 3-CCD camera may cost $10,000 (for 1,524 x 1,012 x 36 bit) up to $30,000 (for 3,060 x 2,036 x 14 bit). CCD scanners for teleradiology are less expensive than laser scanners, and may not have the same ability to detect contrast. This may or may not affect their ability to transmit diagnostic quality images.

Hue and saturation (color) on a video monitor

Cine loop
Also called 'paging.' The rapid, repeating display of sequential images in movie fashion. This display method plays a limited number of frames, at a limited frame rate, but gives the impression of dynamic motion. Often used in telecardiology applications

Circuit Switched Network
A network that temporarily connects two or more channels between two or more points to provide the user with exclusive use of an open channel to exchange information, also called line switching and dial-up service.

Civilian Health and Medicine Program of the Uniformed Services (CHAMPUS )

Clinical Information System (CIS )
An integrated system for the processing of data related to clinical events. Components of a clinical information system would include traditional areas like lab, x-ray, pharmacy, billing and more innovative areas, such as expert systems, medical records, and patient care at the bedside. The focus of a CIS is on clinical decision-making, whereas a Hospital Information System provide support for all information processing within the organization. The Texas Medical Center has begun a major CIS project.

See universal C-mount

Coder-Decoder (CODEC)
COder/DECoder (also COmpression/DECompression) hardware and/or software used with interactive video systems that converts an analog signal to digital, then compresses it so that lower bandwidth telecommunications lines can be used. The signal is decompressed and converted back to analog output by a compatible CODEC at the receiving end. The compression method (algorithm) may be proprietary or (much preferred) standards - based.

Color Balance
The process of matching the amplitudes of red, green and blue signals so the resulting mixture makes an accurate white color.

Color Burst
The part of an NTSC or PAL composite video signal which provides a reference for the demodulation of the color information in codecs and video monitors.

Color Cycling
A means of simulating motion in a video by changing colors.

Color Keying
To superimpose one image over another for special effects.

Carrier, Common Carrier
A telecommunications company regulated by government agencies that offers communications relay services to the general public via shared circuits, charging published and non- discriminatory rates. Any supplier of transmission facilities or services to the general public authorized by the appropriate regulatory authority and bound to adhere to the applicable operating rules.

Terrestrial Carrier
--A telecommunications transmission system using land-based facilities.

InterExchange Carrier
-- a telephone company such as AT&T, Sprint, or MCI that carries long distance calls. The ICs are authorized by the FCC to carry inter-LATA, interstate traffic and can be authorized by state PUCs to carry inter- LATA, intrastate traffic. Also known as Long Distance Carriers

Long Distance Carrier
(LDC) --
common carriers offering telephone services between local access and transport areas (LATAs).

Long Distance
-- calls between two LATAs.

Bypass Technology
- Communication services that completely the need for any services from the local telephone company (i.e., microwave and satellite).

Point of Presence
-- the point at which an interexchange carrier's circuits connect with local circuits for transmission and reception of long distance phone calls. A switching site maintained by a long distance carrier in a LATA. Local exchange carriers will route long distance calls from their central office to the POP of the appropriate long distance carrier.

Local Exchange Carrier
-- Local Exchange Company. The local telephone office that bridges between the long-distance carrier and the customer site. May be part of an RBOC or an independent telephone company. See LATA, IEC.

Local Access Transport Area
-- the area that includes either one large city and its suburbs or a certain number of people. Calls made within LATAs are serviced by the local exchange carriers while calls made between LATAs are serviced by long distance carriers. Area defined for a company to give local phone service. Outside the LATA is long distance. These are local telephone service areas created by the divestiture of the Regional Bell Operating Companies (RBOCs) formerly associated with AT&T.

Central or Switching Office
-- a local telephone company facility that houses the switching system and related equipment needed to interconnect telephone calls for customers in the immediate geographic area. Every LATA must have at least one central office.

Regional Bell Operating Company
-- One of the seven regional companies formed by the AT&T (American Telephone and Telegraph) divestiture. The RBOCs (Regional Bell Operating Companies) are grouped under the seven regional holding companies.

Independent Telephone Company
-- a local exchange carrier that is not part of the Regional Bell System of Operating Companies (RBOCs).

Metropolitan Area Network
(MAN) --
A geographically extended high-speed LAN designed to interconnect users within a city or metropolitan area.

Asymmetric Digital Subscriber Line
-- currently under trial in several metropolitan areas. Uses existing copper phone lines. With proper retooling by phone companies, these can supply 6 Mbps downstream delivery of data.

Public Switched Telephone Network
-- A network established and operated by communication common carriers or telecommunication administrators for provision of circuit switched, packet switched and leased line circuits to the public.

Plain Old Telephone System (POTS)
The analog, public switched telephone network in common use throughout the world. Also known as Public Switched Telephone Network (PSTN). Enables voice phone calls and data transmission of up to 33.6 Kbps, as well as limited videoconferencing.

Public Data Network
-- Public services whereby companies or governmental agencies supply communication channels for data transmission that technically allow the interconncction of computers of an entire region or country.

Private Network
-- a direct channel created between two institutions.

Private Voice Circuits
-- a non-switched line with a usable bandwidth sufficient for voice communication. The basic elements of a traditional, telephone system.

Private Branch eXchange
-- a telephone switch, typically located at the customer site, connected to the public telephone network but operated by the customer. PBXs may be digital rather than analog.

Direct Inward Dialing
-- a service allowing an outside caller to call directly to an extension within a PBX, eliminating switchboard traffic. While the telephone company provides the service, the customer's PBX must be able to handle the calls.

Telephone System
-- a communications system consisting of lines, switches and customer premises equipment (CPE), e.g., amplifiers, bridges, computer networks, faxes, PBXs, modems, telephones, video, etc. At the smallest level, a telephone system might consist of a telephone and a voice grade circuit connected to a local service. At the global level, a telephone system encompasses transmission of voice, data, and video via satellite, fiber optic lines, and packet switched networks (PSNs).

Key System
A telephone system in which multiple phones share a set number of outside lines and a currently open line must be selected by pushing the corresponding button on the phone.

-- a part of an telephone system composed of one central office, the subscribers whom it serves and the interconnecting lines or wires.

Direct Dial Central Office
-- Local telephone trunks connecting a telephone system to a central office. These provide regular local dial-up service.

Value Added Service
-- utilizing common carrier networks for transmissions and providing additional data services with separate equipment.

-- the physical medium that connects individual extensions and stations to a PBX within a building.

Switched line or network
-- a telecommunications option that operates like a dial-up phone line (which is, in fact, a switched line-as are ISDN, ATM, switched 56). There is often a usage charge for switched services, particularly for long distance connections such as phone lines. Compare to leased line, where the connection is continuously open and charges are usually on a flat, monthly rate.

Leased Lines
-- lines rented from a telephone company for the exclusive use of a customer, may also be called dedicated lines. A method of acquiring telecommunications where a defined level of service is paid for, based on a fixed price.

-- a large capacity, long distance channel used by common carriers to transfer information between its customers. The physical medium that connects the major components of a telecommunication system, both of which are switching centers or individual distribution points (the private branch exchange, central office, points of presence, etc.)

Dedicated (Leased,Private) Line
-- permanent connections between two telephones or PBXs. The route and circuit are always available to the person who leases or owns the lines and the signal does not need to be switched.

-- the process of or the facilities involved in establishing a temporary connection via the switched telephone network.

(PPP )
-- internal telephone systems located on the premises of many large offices. The switch located on the customer's premises primarily establishes voice graded circuits over tie lines between individual users and the switched telephone network (PSTN).

Tie Line
(Tie Trunk)
-- a leased or dedicated telephone circuit provided by common carriers that links two points together without using the switched telephone network.

Switched 56
-- a
dial-up 56 Kbps digital line, billed at a monthly rate + cost/minute, as with a regular POTS phone line.

Leased 56
-- a leased line providing a transmission rate of 56 Kbps.
Common Intermediate Format (CIF)
an international standard for video display formats developed by the TSS (see ITU-T). See FCIF, QCIF.

Communication Multiplexer
A device that allows data from multiple, lower speed, communication lines to share a single higher speed communication path.

Communications Frame Structure (CFS)

Community Health Information Network (CHIN)
A CHIN provides a common communications system for health professionals, patients and the community. It integrates the Hospital Information System with medical databases, community health information, and on-line services. It is a central resource for hospital information, e.g., policies and procedures, scheduling, etc.

Compander COMPresser/expANDER
Both A-law and Mu-law companders are used in telephony to improve the subjective signal-to-(quantizing) noise ratio for audio communications and telephony.

The ability for computer programs and computer readable data to be transferred from one hardware system to another without losses, changes or extra programming.

Comparison Category Rating (CCR).
An ITU-T P.800 subjective test where the signal from the device under test is compared to a known quality signal and may be rated from beeter to worse. This is a test performed by HEI.

Comparison Mean Opinion Score (CMOS)
Subjective testing case: Comparison Mean Opinion Score, ITU-T P.800 subjective listening tests where the test subject compares samples of signals passing through the device under test with a know reference signal, testing carried out by HEI.

Component video
Compared to composite video, keeps the chrominance and luminance parts of the video signal separate, yielding better image quality, higher lines of resolution, and better color.

Composite Health Care System (CHCS)

Composite video
Color TV evolved from black/white systems that were developed over 50 years ago. A separated red, green, and blue color broadcast used in RGB would have taken three times the bandwidth of existing black/white approaches. An ingenious solution to conserve bandwidth was to create a separate chrominance signal for color that could be overlaid onto the existing luminance signal, without increasing bandwidth. The result: composite video. Because of potential interference between the chrominance and luminence, composite video requires periodic adjustment to assure 'true' color. Used with NTSC and PAL systems.

Compressed Video
Video images that have been processed to remove redundant information, reducing the amount of bandwidth needed to capture the necessary information so that the information can be sent over narrowband carriers such as a T1 telephone line.

Compression, data
The process of reducing the quantity of data necessary to transmit or store. See also below.

Compression, adaptive
Data compression software that continually analyzes and compensates its algorithm, depending on the type and content of the data and the storage medium.

Compression, asymmetrical
A system which requires more processing capability to compress an image than to decompress an image. It is typically used for the mass distribution of programs on media such as CD-ROM, where significant expense can be incurred for the production and compression of the program but the playback system must be low in cost.

Compression, symmetrical
A compression system which requires equal processing capability for Compression and decompression of an image. This form of compression is used in applications where both compression and decompression will be utilized frequently. Examples include: still-image databasing, still-image transmission (color fax), video production, video mail, videophones, and videoconferencing.

Compression, lossless
A process which allows data compression and its expansion to its original form without any loss of information. PKZip, ZOO and ARC are common examples. See also Huffman Coding.

Compression, lossy
A process which compresses data in such a manner as to make complete recovery of the original data impossible. This process is commonly used for still or motion images where the recovered image only needs to be subjectively acceptable. Examples include JPEG, MPEG, H.261. Note that lossy compression provides significantly greater possible compression than lossless compression. See also Cosine Transform.

Compression ratio
The amount that an image is "compressed" using mathematical algorithms to decrease the amount of data that needs to be stored or transmitted. An uncompressed NTSC (broadband, broadcast quality) signal transmits at about 90 Mbps; this can be compressed using a CODEC to 384 Kbps (more than 200:1 compression); the resulting image is adequate for most clinical applications. "Lossless compression" loses no data; generally data compressed more than three times (3:1) is considered "lossy." This is true of the JPEG compression algorithm. Some compression algorithms (wavelets) support a higher compression ratio (10:1 or higher) before becoming "lossy." See also MPEG.

Computed-based Patient Record (CPR)
A term for a paperless, (electronic) medical record. Such development has occured in the ancillary services, e.g. lab and x-ray. A completely computer-based patient record remains part of the future of Medical Informatics. There are issues of storage and accessibility plus security and confidentiality.

Computed Tomography (CT)

Computer Conferencing
Group communications through computers, or the use of shared computer files, remote terminal equipment and telecommunications channels for two-way, real time, group communication.

Conditional Replenishmen
In motion video compression, the conditional transmission of information from blocks of pixels in adjacent video frames only if the content has changed materially.

Conference Call
A telephone call that uses a bridge to connect more than two individuals at geographically distant locations for simultaneous conversation.

The ability of disparate devices to be connected into a single system.

Consultative Committee for International Telegraphy and Telephony (CCITT)
The forerunner of the ITU's Telecommunications Standardization Sector (TSS). An international standards organization dedicated to creating communications protocols that will enable global compatibility for the transmission of voice, data, and video across all computing and telecommunications equipment.

Continuous Presence
A video processing, transmission and display technique which electronically combines parts of two separate video images for transmission in a single data stream. At the receive location, the images may be displayed on a single monitor or alternatively on two side-by-side monitors. In practice, continuous presence is generally implemented by extracting the horizontal center half of the video image from two cameras and electronically stacking the two halves into a single video signal for transmission. At the receive location, both images may be viewed stacked on a single video monitor, one above the other, or separated for viewing on side-by-side monitors.

Cosine Transform (DCT)
The two-dimensional discrete cosine transform (DCT) developed in 1981 by Wen-hsiung Chen (Chief Scientist, Compression Labs, Inc., San Jose, CA) serves as the basis of most lossy still-image and motion video compression in standards including JPEG, MPEG and H.261. The DCT converts blocks of picture elements from the vertical and horizontal spatial domains to the transform domain (or put another way, pixels from rows and columns are converted to the frequency domain). Depending on a number of factors, the coefficients produced may be truncated by varying degrees prior to storage or transmission without subjectively affecting the recovered images.


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