Glossary
2 Wire Telephone
This is the standard subscriber dial up type line. Send and receive data pass over the same pair of wires.
4 Wire Telephone
Dedicated voice and data lines are often 4-wire circuits. One pair is used for transmit and the other pair for receive, allowing simultaneous two-way transmission.
AMI
Alternate Mark Inversion, a data format where successive 1’s in data are represented by alternating plus & minus pulses on the line. This allows transformer coupling of the data lines. This signal format is used in T-1 and E-1 systems.
ASI
Alternate Space Inversion, a data format where successive 1’s in data are represented by alternating plus & minus pulses on the line. This allows for transformer coupling of the data lines. This signal format is used in ISDN systems.
Asynchronous
A communications mode where data signals occur at random intervals unregulated by clock pulses. Each character is bracketed with a start and stop pulse to assure recognition by the communications terminal.
Balanced mode
A transmission mode where each signal path uses two wires and both wires of the pair are at a potential other than ground, e.g. RS-422, MIL-188-144.
Composite video
A television video format where the color information is included in the video signal and not sent separately as it is in the red, green, blue (RGB) system.
Contact format
Contact forms describe the number of circuits they switch and their normal, inactivated state. FORM A – Single pole, single throw, normally open. FORM B – Single pole, single throw, normally closed. FORM C – Single pole, double throw, break before make. FORM D – Single pole, double throw, make before break. FORM K – single pole, double throw, normally open, (center off).
DCE
Data Communications Equipment, transmission equipment which interfaces with the communications line, e.g. a multiplexer unit or a modem
DTE
Data Terminal Equipment, the source device from which data transmission originates, e.g. a computer terminal.
Duplex
A communications mode where data may be simultaneously passed in both directions. Known also as full duplex. This mode uses two transmission paths to send and receive. EIA-530 Defines a physical data interface using the DB-25 connector to carry balanced RS-422 signal circuits.
Elastic Buffer
An electronic system which takes data in from one source and clock rate and puts it out to a different source at a slightly different clock rate. The buffer is used for instance, to match speeds between satellite and earth station communications circuits to compensate for Doppler shift.
E-1 (CEPT)
E-1 is a data communications specification which defines both an electrical and physical interface. The system uses balanced lines and a signal level that is ± 3 volts around 0 volts. The data rate is 2.048 Mbps.
E & M Control Leads
E & M leads (originally ear and mouth) are signaling lines which are used on telephone circuits for control purposes. There are 5 standard signaling configurations using the E, M, ground, and -48 volt battery lines. See page 1-16-2 of this catalog for schematic diagrams of the configurations.
Interface Conversion
Changing signals from one set of levels to another, e.g. RS-232 TO MIL-188-C, or one protocol to another, e.g. balanced to unbalanced.
ISDN
The Integrated Services Digital Network (ISDN) data communication specification defines both an electrical interface, and a physical configuration protocol. The system uses balanced lines and a signal level of ± .75 volts around 0 volts. The Basic Rate Interface (BRI) consists of 2 data channels of 64 Kbps each and one control channel of 16 Kbps known also as 2B+D.
MIL-188-C
A data communication electrical interface protocol which uses unbalanced lines, and signal levels which vary ± 6 volts, ± 1 volt around 0 volts.
MIL-188-114
A data communication electrical interface protocol which, most often, uses balanced lines and signal levels varying between ± 3 volts around 0 volts. There is also an unbalanced version of the spec.
Multi-mode fiber
Fiber optic cable with a large light conducting core, most commonly 62.5 microns in diameter.
Null modem
A method for connecting terminal devices (DTE) so that they can communicate with each other directly as if there were communications devices (DCE) in line.
RS-170 video
The video specification (timing, format, impedance, etc.) which defines the NTSC broadcast video standard that is used in the United States.
RS-232
A data communications electrical interface protocol which defines unbalanced lines, and signal levels which can vary between ± 3 to ±25 volts.
RS-422
A data communications electrical interface protocol which uses balanced lines, and signal levels which vary between ± 3 volts offset ± 6 volts.
RS-423
A data communication electrical interface protocol which uses unbalanced lines, and signal levels that vary between ± 6 volts around 0 volts.
SCIF
Sensitive Compartmented Information Facility
Simplex
A communications mode where data passes in one direction.
Single-mode fiber
Fiber optic cable with a small light conducting core, most commonly 9 microns in diameter. Used when signal paths extend beyond several miles.
Synchronous
A communications mode where data signals are sent at precise intervals that are regulated by a system clock. Additional start and stop pulses are not required.
Tail circuit
That portion of a communications circuit that falls between the terminal device, (DTE, e.g. data source or destination) and the first communication device (DCE, e.g., modem or multiplexer.
Telephone Trunk Circuit
Circuits between the telephone companies central offices or to major users having multiple lines.
Timing Distribution System
An electronic system which distributes either RF clock frequencies (e.g. 5 MHz) from a reference standard such as a Cesium clock or one which creates DATA rate clocks from such an RF input. These clock rates are used to synchronize communications circuits to assure compatible clock rates.
T-1
T-1 is a data communications specification which defines both an electrical and physical interface. The system uses balanced lines and a signal level that is ± 3 volts around 0 volts. The data rate 1.544 Mbps. The system provides 24 channels of 64 Kbps data.
TEMPEST
Telecommunications Electronics Material Protected from Emanating Spurious Transmissions
Unbalanced
A transmission mode where each data path uses a single wire and a common signal ground return, e.g. RS-232, MIL-188-C.
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