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Glossary
I
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" (for example, "4CF h", read "four charley fox, hex"). The result is that one hex digit represents a 4-bit value.
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 less 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) whose 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
(for example, 129.128.44.227).
Internet Protocol (IP): A protocol used to route data from its source to its destination in an Internet environment. The Internet Protocol was
designed to connect to local area networks. Although there are many protocols that do this, IP refers to the global system of interconnecting
computers. It is a highly distributed protocol (each machine only worries about sending data to the next step in the route).
Internetwork Packet Exchange (IPX): A NetWare communications protocol used to route messages from one node to another. IPX packets
include network addresses and can be routed from one network to another. An IPX packet can occasionally get lost when crossing networks,
thus IPX does not guarantee delivery of a complete message. Either the application has to provide that control, or NetWare's SPX protocol
must be used.
Interoperable: Devices from different vendors that can exchange information using a standard's base protocol.
I/O Addresses: Locations within the I/O address space of your computer used by a device, such as an expansion card, a serial port, or an
internal modem. The address is used for communication between software and a device.
IRQ Level (Interrupt Request Level): The notification a processor receives when another portion of the computer's hardware requires its
attention. IRQs are numbered so that the device issuing the IRQ can be identified, and so IRQs can be prioritized.
ISA (Industry Standards Architecture) (pronounced "ice a"): The classic 8 or 16-bit architecture introduced with IBM's PC-AT computer.
ISDN (Integrated Services Digital Network): An International telecommunications standard for transmitting voice, video and data over a
digital communications line. ISDN is a world-wide telecommunications service that uses digital transmission and switching technology to
support voice and digital data communications. Frame relay was partially based on ISDN's data link layer protocol (LAPD). Frame relay can
be used to transmit across ISDN services offering circuit-switched connection at 64K bps and higher speeds. Contrast Public Switched
Telephone Network (PSTN).
ITU-TSS (formerly CCITT): International Telecommunications Union-Telecommunications Sector; the United Nations organization that
prepares standards ("Recommendations") for resolving communications issues and problems.
K
Key Telephone System (KTS): Phone devices with multiple buttons that let you select incoming or outgoing CO phone lines directly. Similar
in operation to a PBX, except a KTS you don't have to dial a "9" for a call outside the building.
Key Service Unit (KSU): A small device containing the switching electronics for a business key telephone system (KTS).
Key Set: A telephone set with several buttons for call holding, line pickup, intercom, autodialing, and so on. Also called a touchtone phone
(Ericsson) and a KTS (Key Telephone Set).
L
LAPB: Link Access Procedure Balanced; based on the X.25 Layer 2 specification. A full-duplex point-to-point bit-synchronous protocol
commonly used as a data link control protocol to interface X.25 DTEs. LAPB is the link initialization procedure that establishes and maintains
communications between the DTE and the DCE.
LAPD: Link Access Protocol for the D-Channel; based on the ISDN Q.921 specification. A full-duplex point-to-point bit-synchronous link-level
protocol for ISDN connections; different from LAPB in its framing sequence. Transmission is in units called "frames", and a frame may
contain one or more X.25 packets.
Line Coding: The representation of 1s and 0s on a T1 line. The two methods of line coding commonly used, B8ZS and AMI, differ in the
restrictions placed on user data. T1 line coding ensures that sufficient timing information is sent with the digital signal to ensure recovery of
all the bits at the far end. Timing information on the T1 line is included in the form of 1s in the data stream; a long string of 0s in the data
stream could cause problems recovering the data.