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Glossary
Foreign Exchange Office (FXO): provides local telephone service from a CO outside of ("foreign" to) the subscriber's
exchange area. In simple form, a user can pick up the phone in one city and receive a tone in the foreign city. Connecting a
POTS telephone to a computer telephony system via a T1 link requires a channel bank configured for the FX connection. To
generate a call from the POTS set to the computer telephony system, a FXO connection must be configured.
Foreign Exchange Station (FXS): See FX, FXO. To generate a call from the computer telephony system to the POTS set,
an FXS connection must be configured.
Forward Explicit Congestion Notification (FECN): A bit that tells you that a certain frame on a particular logical
connection has encountered heavy traffic. The bit provides notification that congestion-avoidance procedures should be
initiatedin the same direction of the received frame. See also BECN (Backward Explicit Congestion Notification).
Frame: A group of data bits in a specific format to help network equipment recognize what the bits mean and how to
process them. The bits are sent serially, with a flag at each end signifying the start and end of the frame.
Frame Relay: A form of packet switching that uses small packets and that requires less error checking than other forms of
packet switching. Frame relay is effective for sending "bursty" data at high speeds (56/64K, 256K, and 1024 Kbps) over
wide area networks. Frame Relay specifications are defined by ANSI documents ANSI T1.602, T1.606, T1S1/90-175, T1S1/
90-213, and T1S1/90-214. In using frame relay, blocks of information (frames) are passed across a digital network interface
using a "connection number" that is applied to each frame to distinguish between individual frames.
Frame Relay Forum: A non-profit organization of 300+ vendors and service providers, based in Foster City, CA, that are
developing and deploying frame relay equipment.
Frame Relay Implementors Forum: A group of companies supporting a common specification for frame relay connection
to link customer premises equipment to telco network equipment. Their specification supports ANSI frame relay specs and
defines extensions such as local management.
Frame Relay Access Device (FRAD): A piece of equipment that acts as a concentrator or frame assembler/dissassember
that can support multiple protocols and provide basic "routing" functions.
G
Gateway: 1. A functional unit that interconnects two computer networks with different network architectures. A gateway
connects networks or systems of different architectures. A bridge interconnects networks or systems with the same or
similar architectures. 2. A network that connects hosts.
Graphical User Interface (GUI): A type of computer interface consisting of a visual metaphor of a real-world scene, often
of a desktop. Within that scene are icons, representing actual objects, that the user can access and manipulate with a
pointing device.
H
Handshaking: A process that two modems go through at the time of call setup to establish synchronization over the data
communications link. It is a synchronization and negotiation process accomplished by the exchange of predefined, mutually
recognized control codes.
Hexadecimal: A base 16 numbering system used to represent binary values. Hex uses the numbers 0-9 and the letters A-F:
usually notated by an "h" (e.g., "4CF h", read "four charley fox, hex"). The result is that one hex digit represents a 4-bit
value.
High-level Data Link Control (HDLC): An ISO standard, bit-oriented data communications protocol that provides nearly
error-free data transfers.
I
Implicit congestion management: A method of informing the terminal that the network is busy. This method relies on the
end-system protocol to detect and fix the congestion problem. (TCP/IP is an example of a protocol using only implicit
congestion management.) See also "explicit congestion management".
In-band: Refers to the type of signalling over the conversion path on an ISDN call. Contrast "out-of-band".
Insufficient Ones: A T1 error condition that is logged when fewer than one 1 in 16 0s or less than 12.5 % average 1s
density is received.
Inter Exchange Carrier (IEC): The long distance company (LE) who's central office provides the point of reference for T1
access. Any common carrier authorized by the FCC to carry customer transmissions between LATAs.
Internet: Refers to the computer network of many millions of university, government and private users around the world.
Each user has a unique Internet Address.
Internet Address (IP Address): A unique 32-bit address for a specific TCP/IP host on a network. Normally printed in dotted
decimal format (e.g., 129.128.44.227).
MTPSR3-200
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