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Glossary: CCNA & General Networking Terms 


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A physical layer communications specification for 10Mbps, baseband data transmission over a coaxial cable (Thinnet) with a maximum cable segment length of 200 meters. [Source: RFC1983]
A physical layer communications specification for 10Mbps, baseband data transmission over a coaxial cable (Thicknet) with a maximum cable segment length of 500 meters. [Source: RFC1983]
A physical layer communications specification for 10Mbps, baseband data transmission over a fiber-optic cable. [Source: RFC1983]
A physical layer communications specification for 10Mbps, baseband data transmission over a twisted-pair copper wire. See also: Ethernet, twisted pair. [Source: RFC1983]
The set of IEEE Working Groups and subsequent standards for the definition of wireless LAN protocols. The Physical Layer (air interface) incorporates Spread Spectrum techniques to avoid detection, interception and interference between devices. The results so far are 802.11b, which has a data rate of 11Mbit/s and uses the 2.4GHz radio band, then 802.11a which has a data rate of 54Mbit/s and uses the 5GHz radio band, so it is not inherently interoperable with 802.11b. Subsequently 802.11g has a data rate of greater than 20MBit/s with the 2.4GHz range, so there is scope for interworking with 802.11b devices. Then 802.11h enhances the 802.11a standard to select frequencies and trim power output to avoid interference with HIPERLAN devices in Europe which use the same 5GHz band. The 2.4GHz and 5GHz radio bands are licence exempt so are attractive to general users.

There is a built-in security method, Wired Equivalent Privacy (WEP) within 802.11b standard, but there is an initial move to use 802.1x security mechanisms before 802.11i is fully developed to enhance security and authentication mechanisms (ongoing at March 2003). See also: 802.x, Bluetooth, HIPERLAN, IEEE, Spread Spectrum, Wired Equivalent Privacy, Wireless Local Area Network.

The set of IEEE Working Groups and subsequent standards for the definition of fixed and wireless LAN and MAN protocols. See also: 802.11, Bluetooth, IEEE, Wireless Local Area Network.
See: RFC 822


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Address record for a host of given name in Domain Name Service.
Aberdeen Metropolitan Area Network.
abstract syntax
A description of a data structure that is independent of machine- oriented structures and encodings. [Source: RFC1208]
Abstract Syntax Notation One (ASN.1)
The language used by the OSI protocols for describing abstract syntax. This language is also used to encode SNMP packets. ASN.1 is defined in ISO documents 8824.2 and 8825.2. See also: Basic Encoding Rules. [Source: RFC1392]
Acceptable Use Policy (AUP)
Many transit networks have policies which restrict the use to which the network may be put. For example, some networks may only be used for non-commercial purposes. Some AUPs limit the type of material which can be made available to the public (e.g., pornographic material). Enforcement of AUPs varies with the network. See also: netiquette. [Source: RFC1983]
Access Control List (ACL)
Most network security systems operate by allowing selective use of services. An Access Control List is the usual means by which access to, and denial of, services is controlled. It is simply a list of the services available, each with a list of the hosts permitted to use the service. [Source: RFC1392]
See: Acknowledgment
acknowledgment (ACK)
A type of message sent to indicate that a block of data arrived at its destination without error. See also: Negative Acknowledgement. [Source: NNSC]
See: Access Control List
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. [Source: RFC1208]
See: Administrative Domain
There are four types of addresses in common use within the Internet. They are email address; IP, internet or Internet address; hardware or MAC address; and URL. See also: email address, IP address, internet address, MAC address, Uniform Resource Locator. [Source: RFC1983]
address mask
A bit mask used to identify which bits in an IP address correspond to the network and subnet portions of the address. This mask is often referred to as the subnet mask because the network portion of the address (i.e., the network mask) can be determined by the encoding inherent in an IP address. See also: Classless Inter- domain Routing. [Source: RFC1983]
address resolution
Conversion of a network-layer address (e.g. IP address) into the corresponding physical address (e.g., MAC address). See also: IP address, MAC address. [Source: RFC1983]
Address Resolution Protocol (ARP)
Used to dynamically discover the low level physical network hardware address that corresponds to the high level IP address for a given host. ARP is limited to physical network systems that support broadcast packets that can be heard by all hosts on the network. It is defined in RFC 826. See also: proxy ARP, Reverse Address Resolution Protocol. [Source: RFC1983]
Administration Management Domain. An 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. See PRMD. [Source: RFC1208]
Administrative Domain (AD)
A collection of hosts and routers, and the interconnecting network(s), managed by a single administrative authority. [Source: RFC1392]
Administrative tasks, most often related to the maintenance of mailing lists, digests, news gateways, etc.
Advanced Research Projects Agency (ARPA)
An agency of the U.S. Department of Defense responsible for the development of new technology for use by the military. ARPA (formerly known as DARPA, nee ARPA) was responsible for funding much of the development of the Internet we know today, including the Berkeley version of Unix and TCP/IP. [Source: NNSC]
Advanced Research Projects Agency Network (ARPANET)
A pioneering longhaul network funded by ARPA. It served as the basis for early networking research, as well as a central backbone during the development of the Internet. The ARPANET consisted of individual packet switching computers interconnected by leased lines. See also: Advanced Research Projects Agency. [Source: FYI4]
In the client-server model, the part of the system that performs information preparation and exchange on behalf of a client or server application. [Source: RFC1208]
A name, usually short and easy to remember, that is translated into another name, usually long and difficult to remember. [Source: RFC1392]
American National Standards Institute (ANSI)
This organization is responsible for approving U.S. standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards (e.g., ANSI C is the version of the C language approved by ANSI). ANSI is a member of ISO. See also: International Organization for Standardization. [Source: NNSC]
American Standard Code for Information Interchange (ASCII)
A standard character-to-number encoding widely used in the computer industry. See also: EBCDIC. [Source: RFC1392]
anonymous FTP
Anonymous FTP allows a user to retrieve documents, files, programs, and other archived data from anywhere in the Internet without having to establish a userid and password. By using the special userid of "anonymous" the network user will bypass local security checks and will have access to publicly accessible files on the remote system. See also: archive site, File Transfer Protocol, World Wide Web. [Source: RFC1983]
See: American National Standards Institute
Asia and Oceania Workshop. One of the three regional OSI Implementors Workshops, equivalent to OIW and EWOS.
See: Application Program Interface
A networking protocol developed by Apple Computer for communication between Apple Computer products and other computers. This protocol is independent of the network layer on which it is run. Current implementations exist for Localtalk, a 235Kb/s local area network; and Ethertalk, a 10Mb/s local area network. [Source: NNSC]
A program that performs a function directly for a user. FTP, mail and Telnet clients are examples of network applications. [Source: RFC1392]
application layer
The top layer of the network protocol stack. The application layer is concerned with the semantics of work (e.g., formatting electronic mail messages). How to represent that data and how to reach the foreign node are issues for lower layers of the network. [Source: MALAMUD]
Application Program Interface (API)
A set of calling conventions which define how a service is invoked through a software package. [Source: RFC1208]
A system to automatically gather, index and serve information on the Internet. The initial implementation of archie provided an indexed directory of filenames from all anonymous FTP archives on the Internet. Later versions provide other collections of information. See also: archive site, Gopher, Prospero, Wide Area Information Servers. [Source: RFC1392]
archive site
A machine that provides access to a collection of files across the Internet. For example, an anonymous FTP archive site provides access to arcived material via the FTP protocol. WWW servers can also serve as archive sites. See also: anonymous FTP, archie, Gopher, Prospero, Wide Area Information Servers, World Wide Web. [Source: RFC1392]
See: Address Resolution Protocol
See: Defense Advanced Research Projects Agency
See: Advanced Research Projects Agency Network
See: Autonomous System
See: American Standard Code for Information Interchange
See: Abstract Syntax Notation One
assigned numbers
The RFC [STD2] which documents the currently assigned values from several series of numbers used in network protocol implementations. This RFC is updated periodically and, in any case, current information can be obtained from the Internet Assigned Numbers Authority (IANA). If you are developing a protocol or application that will require the use of a link, socket, port, protocol, etc., please contact the IANA to receive a number assignment. See also: Internet Assigned Numbers Authority, STD. [Source: STD2]
Transmission by individual bytes, not related to specific timing on the transmitting end.
Asynchronous Transfer Mode (ATM)
A standard which defines high-load, high-speed (1.544Mbps through 1.2Gbps), fixed-size packet (cell) switching with dynamic bandwidth allocation. ATM is also known as "fast packet." [Source: RFC1983]
See: Asynchronous Transfer Mode
See: Acceptable Use Policy
The form of information items provided by the X.500 Directory Service. The directory information base consists of entries, each containing one or more attributes. Each attribute consists of a type identifier together with one or more values. Each directory Read operation can retrieve some or all attributes from a designated entry. [Source: RFC1208]
Australian Computer Emergency Response Team.
The verification of the identity of a person or process. [Source: MALAMUD]
Something which happens pseudo-automatically, and is usually too complex to go into any further than to say it happens ``auto-magically.''
Autonomous System (AS)
Internet (TCP/IP) terminology for a collection of routers under a single administrative authority using a common Interior Gateway Protocol (IGP) for routing packets. See subnetwork. [Source: RFC1392]


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