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A
A
and B Bit Signaling
These
are the bits used in T1 transmission links that convey signaling
information. These bits are used to carry dialing and control information
such as off hook and dial tone for each voice conversation that is
carried across a T1 link.
A to D Conversion
Analog
to digital conversion is also called A to D conversion or ADC. It is the
process of converting an analog waveform into binary format. The most
common example of this is found in the codec (coder/decoder). This device
takes the analog voice signal and converts it to digital (binary) format
for transmission over a digital path such a T1.
AAL
The ATM
adaption layer is an end-to-end process used only by the two
communicating entities to insert and remove data from the ATM layer. At
every point in the network, processing is done only on each ATM cell in
isolation. At no point is it necessary to gather more information than is
contained in a single cell header to complete the process. The network is
not concerned with arrivals of groups of cells, sequencing or
acknowledgment. The AAL enhances the service provided by the ATM layer to
a level required by the next highest layer.
AARP
When using
other Data Link Layer protocols below DDP, a fundamental problem exists
of address matching. This problem arises because of the two different
types of addresses (Link Layer and Network Layer) which must be resolved.
The matching the Link Layer address to the Network Layer address is
resolved by using the AppleTalk Address Resolution Protocol (AARP), which
is similar to the Address Resolution Protocol (ARP) used in the TCP/IP
protocol stack. AARP is used to resolve (or bind) Ethernet addresses to
DDP. When Ethernet sends frames containing DDP, the DDP packet is
encapsulated by the Ethernet frame. These services, together with the
mechanisms used by the Ethernet data link, are referred to as ELAP.
AUI
AUI stands for
Attachment Unit Interface. It is a connector that attaches Ethernet
equipment such as a workstation or fan-out box to a transceiver. AAUI is
the AppleTalk Attachment Unit Interface.
ABM
ABM stands for
Asynchronous Balanced Mode. ABM is one of three types of data transfer
modes in the HDLC family of protocols:
- Normal Response
Mode (NRM). Used in the unbalanced configuration, secondary may only
respond to a poll from the primary station.
- Asynchronous
Balanced Mode (ABM). Either station may initiate transmission (balanced
configuration).
- Asynchronous
Response Mode (ARM). Either station may initiate transmission but
one station has responsibility for line maintenance such as error
recovery.
Abbreviated Dialing
Abbreviated
dialing enables a caller to dial a frequently used number by using only a
few of the digits instead of the entire telephone number. Abbreviated
dialing is also referred to as speed dialing and short-code dialing.
Abstract Syntax Notation
ASN.1
stands for Abstract Syntax Notation One. It provides a standardized
format for data transfer between nodes. Each node is only concerned with
translating to and from ASN.1 and doesn't need to know anything about the
format in which data are stored elsewhere on the network.
ACK
ACK is short
for acknowledgment. In data communications a node will send an ACK to
another node to indicate a transmitted frame or packet has been received.
Connection-oriented protocols use acknowledgments.
Access Charge
An access
charge is the cost assessed to telecommunications users for access to the
local or regional exchange to send or receive calls. It also refers to
access of specialized telecom services to originate and receive
interstate toll calls, as well as access to the customer's local access
and transport area (LATA).
Access Method
An
Access Method is a software component in a processor for controlling the
flow of information through a network. Typically this term is used in an
IBM SNA environment for products such as VTAM (Virtual Telecommunications
Access Method). In local area networks, the access method is the
technique and/or program code used to arbitrate the use of the
communications medium by granting access selectively to individual
stations. Examples of LAN access methods are CSMA/CD (Ethernet) and token
passing (Token Ring).
Access Router
An access
router is a router designed for connecting a remote site to a wide area
network or network backbone.
ACD
An Automatic
Call Distributor (ACD) is a specialized telephone system used to
distribute a large volume of incoming calls uniformly to a number of
telephone operators or agents. Common reasons for implementing ACD is for
help desks or order processing.
ACSE
ACSE stands for
the Association Control Service Element. The method used in OSI for establishing
a call between two applications. Checks the identities and contexts of
the application entities, and could apply an authentication security
check.
Adapter Card
An
adapter card is a printed circuit card that fits inside a computer and
communicates information from the computer to another computer or
printer. It takes data from the computer's memory and transfers the data
via a coax cable, RS232 cable or similar connection. An example would be
a 3278 adapter card that fits inside a PC and emulates a 3278 terminal.
Network Interface Cards are examples of specialized adapter cards.
Adaptive Routing
A
method of routing packets (datagrams or messages) in which the computers
along the communications path select the best route for the packet to
take. When network congestion or link failures occur, the path the packet
takes changes or adapts.
Adaptive Bridges
These
are bridges that have the intelligence to route frames with only the
information available in the frame itself (MAC address). Adaptive bridges
broadcast messages across the network when they are first turned on to
gain access to addresses within the network. Adaptive bridging takes
place when the sending and receiving nodes are not even aware that a
bridge exists between them. Adaptive bridges are also called learning
bridges and transparent bridges.
ADC
ADC stands for
Analog to Digital Conversion. It is the process of converting an analog
waveform into binary format. The most common example of this is found in
the Codec (Coder/Decoder). This device takes the analog voice signal and
converts it to digital (binary) format for transmission over a digital
path such a T1.
Address
An address is a
unique identifier that determines the originating location of data or the
destination of data being transmitted across a communications link. There
is a distinction between a station's link address, a station's network
address and an individual process running on a station.
Address Mapping
Two
of the addresses found in networks are physical addresses (NIC addresses)
and logical (or software) addresses. Logical addresses are translated or
"mapped" to physical addresses. Two protocols used by IP to
accomplish this mapping (or discovery) are ARP (Address Resolution
Protocol) and RARP (Reverse Address Resolution Protocol).
Address Mask
Address
mask is a bit mask used to select bits from an Internet address for
subnet addressing. The mask is 32 bits long and selects the network
portion of the Internet address and one or more bits of the local
portion. It is also called a subnet mask.
Address Resolution Protocol
Also
referred to as ARP. It is the Data Link Layer protocol used by IP (as in
TCP/IP) for address resolution. Address resolution refers to the ability
of a machine to resolve another station's MAC (hardware) address given
its IP address.
ADMD
ADMD stands for
Administration Management Domain. It is a X.400 Message Handling System
public service carrier. Examples: MCImail and ATTmail in the U.S., British Telecom Gold400mail in
the U.K. The ADMDs in all countries
worldwide together provide the X.400 backbone.
ADPCM
ADPCM stands
for Adaptive Differential Pulse Code Modulation. ADPCM is a speech
encoding technique allowing analog voice conversations to be carried
within a 32Kbps channel (as opposed to the standard 64Kbps channel).
ADSL
ADSL stands for
Asymmetrical Digital Subscriber Line. It is the Bellcore standard for
one-way T1 transmission to the home over the local loop. It is designed
to carry video to the home.
ADSP
ADSP stands for
AppleTalk Data Stream Protocol (ADSP). ADSP ensures reliable service
between sockets.
Agent
In the
client/server model, an agent is the part of the system that performs
information preparation and exchange on behalf of a client or server
application.
AFP
AFP stands for
AppleTalk File Protocol. This is Apple's network protocol used to provide
file access between servers and clients in an AppleShare network
configuration.
Aggregate Bandwidth
Aggregate
bandwidth is the total bandwidth of a channel that carries multiple bit
streams. For example, the aggregate bandwidth of a T1 channel is 1.544
Mbps consisting of 24 64Kbps channels including 8k of signaling
information.
AIX
AIX is IBM's
version of the UNIX operating system. It stands for Advanced Interactive
eXecutive. The Open Software Foundation (OSF) based its first operating
system on AIX. AIX runs on System 370/390 mainframe CPUs as well as the
RS/6000 and PS/2 desktop platforms. It supports TCP/IP and the OSI
communications protocol standards.
ALM
ALM stands for
AppWare Loadable Module. It is a computer telephony application generator
that is used in conjunction with Novell's NetWare.
ALOHA
ALOHA refers to
two protocols developed in the early 1970s at the University of Hawaii. The first ALOHA protocol
developed (pure ALOHA) was a packet-switching system which used radio
frequencies. Stations could transmit data at any given time. Collisions
were reduced by resending packets when a response was not received after
a given time period. Slotted ALOHA is different from pure ALOHA. With
slotted ALOHA each station must wait for certain time slot before
transmission can take place. Using time boundaries or slots, collisions
are reduced.
AMI
AMI stands for
Alternate Mark Inversion. It is the line-coding format in T1 transmission
systems.
Anonymous FTP
Anonymous
FTP allows users who don't have a password or login ID to access certain
files on remote machines. Users can get public domain software from
Internet sites using "anonymous" as the user ID and their
userid@hostname.domain as their password. A database called
"ARCHIE" details the software that is available using the
anonymous FTP method.
ANSI
The American
National Standards Institute (ANSI) is a national voluntary organization
that develops and publishes standards. It develops standards for data
communications, programming languages, magnetic storage media, the OSI
model, office systems and encryption. It is a member of the International
Organization for Standardization (ISO). For the most part ANSI standards
are similar to ISO standards, differing only when unique aspects of North
American systems need to be considered.
ANSI Character Set
ANSI
published two primary character sets. The 7-bit version is identical to
the ASCII code and is in conformance with IA5 (International Alphabet 5).
The American National Standards Institute also publishes an 8-bit
character set definition.
APAD
APAD stands for
Asynchronous Packet Assembler/Disassembler. PAD (Packet Assembler/Disassembler)
is usually used instead of APAD.
ITU-T
developed a set of standards, informally called the Interactive Terminal
Interface (ITI) standards, meant to provide access for terminals and DTEs
that cannot execute the layers of X.25. The standards are X.3, X.28, and
X.29.
The
ITI standards collectively define a "black box" called a packet
assembler/disassembler, or PAD. A PAD "assembles" a stream of
bytes originating from an asynchronous DTE (for example, from a personal
computer) into X.25 packets and transmits them on the X.25 network. Of
course, it performs the reverse operations for data sent back to the DTE.
To
the DTE, the PAD looks like a modem. This means no special software or
hardware must be added to the DTE beyond that needed for ordinary
asynchronous communications. It is also possible to attach the DTE to the
PAD with a point-to-point link using modems.
A
PAD can attach several DTEs, performing a concentrator function by
placing data from more than one DTE into a packet when possible.
API
API stands for
Application Programming Interface. An API is a formally defined
programming language interface. It is software that allows application
programs to interface to lower level services performed by a computer's
operating system. Application programs make function calls that perform
these lower level functions such as transferring files. Programmers can
use these function calls to gain access to services provided by an
operating system. NetBIOS can serve as an API for data exchange.
APPC
APPC stands for
Advanced Peer-to-Peer Communications. It is an IBM protocol allowing IBM
network nodes to communicate in a "peer" arrangement as opposed
to the typical SNA hierarchical arrangement. APPC consists, essentially,
of two "new" Network Addressable Units:
- LU 6.2. A LU
type that supports program-to-program communication, including
communication between programs in peripheral nodes, for example,
file transfers between workstation database programs.
- PU 2.1. A PU
type that supports peer-to-peer communication between peripheral
nodes, such as a PC emulating a 3174 cluster controller.
AppleTalk
AppleTalk is
Apple Computer's LAN for connecting Macintosh computers, printers and
other resources together.
AppleTalk Session Protocol
The
AppleTalk Session Protocol (ASP) opens, maintains, and closes sessions
between sockets.
AppleTalk Transaction Protocol
The
key protocol based on a data transaction model of end-to-end interaction
is the AppleTalk Transaction Protocol (ATP). ATP provides the request-response
transaction paradigm on which the session-oriented services of the
AppleTalk Session Protocol (ASP) and the Printer Access Protocol (PAP)
are based. While ATP is concerned with independent transactions, ASP
provides a sequence of transactions guaranteed to be delivered and
executed in the order in which the transaction requests are sent. PAP
provides a data read/write type of service built with underlying ATP
transactions. PAP is the transport/session protocol used by printers of
the ImageWriter and LaserWriter families working in an AppleTalk
environment.
AppleTalk Remote Access
AppleTalk
Remote Access is a remote asynchronous AppleTalk connection to another
Macintosh and its network via a modem.
Application Programming Interface
(API)
An
API is a formally defined programming language interface. It is software
that allows application programs to interface to lower level services
performed by a computer's operating system. Application programs make
function calls which perform these lower level functions such as
transferring files. Programmers can use these function calls to gain
access to services provided by an operating system. NetBIOS can serve as
an API for data exchange.
APPN
APPN stands for
Advanced Peer-to-Peer Networking. It is an SNA feature offered by IBM
that allows more efficient routing of data between nodes in an SNA
network. It allows remote workstations to communicate in a peer-to-peer
fashion as opposed to a hierarchical arrangement where communication is
controlled via a host computer. APPN was introduced by IBM in 1985 as an
alternative to the growing popularity of client/server computing
technologies.
ARA
ARA stands for
AppleTalk Remote Access. It is a remote asynchronous AppleTalk connection
to another Macintosh and its network via a modem.
ARPANET
ARPANET stands
for Advanced Research Projects Agency Network. It is a DOD (Department of
Defense) network developed by ARPA that is the Advanced Research Projects
Agency of the U.S. Department of Defense. The ARPANET tied business,
government agencies and universities together through its packet network.
It then became the backbone of the Internet in the early 1990's.
ARQ
ARQ stands for
Automatic Retransmission Request. It also stands for Automatic Request
for Repeat. In the event of an error, data communications protocols deal
with retransmission of data using the ARQ method. Essentially when a
receiving station receives a message (frame) containing corrupted data,
it responds with an ARQ which requests the retransmission of the errored
frame.
ASCII
ASCII stands
for American Standards Committee for Information Interchange. ASCII is
one of the two (EBCDIC is the other) most widely used codes. Codes, such
as ASCII codes represent characters, such as keyboard characters. ASCII
uses 7 bits for the 128 elements it represents. For example, when the
character "A" is pressed on the keyboard, the ASCII binary
representation is 100 0001 (hexadecimal 41).
ASN.1
ASN.1 stands
for Abstract Syntax Notation One. It provides a standardized format for
data transfer between nodes. Each node is only concerned with translating
to and from ASN. 1 and doesn't need to know anything about the format in
which data are stored elsewhere on the network.
(ASP)
opens, maintains, and closes sessions between sockets.
Asynchronous Transfer Mode
Three
transfer modes were considered as possible candidates for B-ISDN. These
three transfer modes are:
- Synchronous
Transfer Mode (STM)
- Packet Transfer
Mode (PTM)
- Asynchronous
Transfer Mode (ATM)
Asynchronous Transfer Mode, or ATM, is a cell relay
technology based on small (53 byte) cells. An ATM network consists of
multiple ATM switches which forward each individual cell to its final
destination. ATM can provide transport services for audio, data and video.
Asynchronous Transmission
Asynchronous
operation means simply that bits are not transmitted on any strict
timetable. Transmitting a start bit indicates the start of each
character. After the final bit of the character is transmitted, a stop
bit is sent, indicating the end of the character. The modems must stay in
synchronization only for the length of time that it takes to transmit the
eight bits. If their clocks are slightly out of synch, data transfer will
still be successful.
AUI
AUI stands for
Attachment Unit Interface. It is a connector that attaches Ethernet
equipment such as a workstation or fan-out box to a transceiver.
Autobaud
The ability of
a device such as a modem to automatically change baud rates to match the
baud rate of the companion device at the other end.
Automatic Call Distribution
An
Automatic Call Distributor (ACD) is a specialized telephone system used
to distribute a large volume of incoming calls uniformly to a number of
telephone operators or agents. Common reasons for implementing ACD is for
help desks or order processing.
Automatic Retransmission Request
(ARQ)
ARQ
stands for Automatic Retransmission Request. It also stands for Automatic
Request for Repeat. In the event of an error, data communications
protocols deal with retransmission of data using the ARQ method.
Essentially when a receiving station receives a message (frame)
containing corrupted data, it responds with an ARQ which requests the retransmission
of the errored frame.
Autonomous System
An
autonomous system is an Internet (TCP/IP) term for a collection of
gateways (routers) that fall under one administrative entity and
cooperate using a common Interior Gateway Protocol (IGP).
AWG
AWG stands for
American Wire Gauge. It is a numbering system that specifies the
thickness of the wire. As the thickness of the wire increases, the number
referring to the wire decreases. Examples of common AWG gauges are listed
below.
- RS-232: 22 AWG
- Ethernet
Thinnet (10 Base2): 20 AWG
Ethernet Thicknet (10 Base5): 12 AWG
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