sjg - glossary of terms for telecommunications & data

glossary of terms
	sjg provides you here with a basic guide to some of the terminology & abbreviations used in the field of GSM, data, ip & telecomms
	if a term or abbr needs adding: let us know

Term	Explanation
10base2	Ethernet &IEEE 802.3 standard for baseband LANs using thin coaxial cable & BNC connectors up to 200 meters: data speed = 10 Mbps
10baseT	Ethernet standard for LANs using twisted-pair CAT5/6 cable. data speed = 10 Mbps
100baseT	Ethernet standard for LANs using twisted-pair CAT5/6 cable. data speed = 100 Mbps
802.1D	An IEEE standard for interLAN bridges (specifically between 802.3, 802.4 and 802.5 networks). 802.1D operates at the MAC layer
802.3	An IEEE standard for accessing a LAN using CSMA/CD. Ethernet follows this standard
802.5	An IEEE physical layer standard for a token-ring LAN access method at 4 or 16 Mbps over unshielded twisted-pair cable
A
AAL	ATM adaptation layer - The layer of the ATM protocol stack that parses data into the payload portion of the ATM cell for transport across an ATM network
access control	A security mechanism that determines which operations a user, group, service, or computer is authorized to perform on a computer or on a particular object [eg a file]
ACE	access control entry - An entry in an object's discretionary access control list (DACL) that grants permissions to a user or group. An ACE is also an entry in an object's system access control list (SACL) that specifies the security events to be audited for a user or group
ACPI	Advanced Configuration and Power Interface - An open industry specification that defines power management on a wide range of mobile, desktop, server computers and peripherals. ACPI is the foundation for the OnNow industry initiative that allows system manufacturers to deliver computers that will start at the touch of a keyboard. ACPI design is essential to take full advantage of power management and Plug and Play
address classes	Predefined groupings of Internet addresses with each class defining networks of a certain size. The range of numbers that can be assigned for the first octet in the IP address is based on the address class Class A networks (values 1 to 126) are the largest, with more than 16 million hosts per network Class B networks (128 to 191) have up to 65,534 hosts per network Class C networks (192 to 223) can have up to 254 hosts per network
Address resource record	A resource record used to map a DNS domain name to a host IP address on the network
administrator	Windows XP Professional: a person responsible for setting up & managing domain controllers or local PCs and their user and group accounts, assigning passwords and permissions, and helping users with networking problems. Administrators are members of the Administrators group and have full control over the domain or computer. Windows XP Home Edition: a person who can make system-wide changes to the computer, install software, and who has access to all files on the computer. A person with a computer administrator account has full access to other user accounts on the PC
administration queue	Message Queuing: a queue that stores acknowledgment messages
administrative alerts	Alerts that relate to server and resource use. They notify users about problems in areas such as security and access, user sessions, server shutdown due to power loss (when an uninterruptible power supply is available), directory replication, and printing. When a computer generates an administrative alert, a message is sent to a predefined list of users and computers
active content	Dynamic content, [eg news], that is usually updated from the WWW or a channel
Active Directory data model	A model derived from the LDAP data model. The directory holds objects that represent entities of various sorts, described by attributes. The objects & classes of objects that can be stored in the directory are defined in the schema. For each class of objects, the schema defines the attributes an instance of the class must have, the additional attributes it can have, and the class that can be its parent
active partition	A partition from which an x86-based computer starts up. The active partition must be a primary partition on a basic disk. If you use Windows exclusively, the active partition can be the same as the system volume
active volume	The volume from which the computer starts up. The active volume must be a simple volume on a dynamic disk. You cannot mark an existing dynamic volume as the active volume, but you can upgrade a basic disk containing the active partition to a dynamic disk. Once the disk is upgraded to dynamic, the partition becomes a simple volume that is active
ActiveX	A set of technologies that allows software components to interact with one another in a networked environment, regardless of the language in which the components were created
active loop	A fault condition on an IEEE 802.3 LAN in which there is more than one active route between source & destination nodes. Active loops can occur when more than one bridge is attached to the same LAN
Address ageing	The process that automatically removes infrequently used dynamic MAC addresses after a configurable length of time. Separate ageing times can be configured for addresses associated with stations on the central LAN and remote LANs.
Address filtering	A method of deciding which data packets are allowed through a device. The decision is based on the source and destination addresses of the data packet.
ADSL	Asymmetric Digital Subscriber Line aka 'Broadband': Transports high-bandwidth data from customers [PC / LAN] and the www. The “asymmetric” term refers to the differing rates [upstream & downstream] available with ADSL. Uses existing DELs for its bearer
ADSL Bearer	A DEL that also carries the ADSL [ie a fax line which also provides the ADSL service; the fax would plug in to a microfilter]
affinity	Network Load Balancing: the method used to associate client requests to cluster hosts. When no affinity is specified, all network requests are load balanced across the cluster without respect to their source. Affinity is implemented by directing all client requests from the same IP address to the same cluster host
agent	An application that runs on a Simple Network Management Protocol (SNMP) managed device. The agent application is the object of management activities. A computer running SNMP agent software is also sometimes referred to as an agent
AH	Authentication Header - RFC2402 defines AH. AH provides integrity & authentication through the shared key hashing algorithms (HMAC-MD5, HMAC-SHA1). AH provides authentication for as much of the IP header as possible. AH also authenticates upper level protocol data.
Alerter service	A service used by the server and other services to notify selected users and computers of administrative alerts that occur on a computer. The Alerter service requires the Messenger service
allocation unit	aka Cluster - The smallest amount of disk space that can be allocated to hold a file. All file systems used by Windows organize hard disks based on allocation units. The smaller the allocation unit size, the more efficiently a disk stores information. If you do not specify an allocation unit size when formatting the disk, Windows picks default sizes based on the size of the volume. These default sizes are selected to reduce the amount of space that is lost and the amount of fragmentation on the volume
AM	Amplitude Modulation - Modulation method used by modems, radio, and DSL equipment. The signal modulates [or alters] the amplitude or intensity of the carrier. In regular AM, the carrier is a sinewave. The amplitude of the modulated carrier changes in proportion to signal amplitude. AM creates two identical sidebands on either side of the carrier. These sidebands contain the signal data. Either sideband can be attenuated or suppressed without harming the signal data. With an equivalent signal, AM tends to require less bandwidth than FM does. AM's disadvantage is that it’s more subject to impulse noise and static than FM
Analog loopback	method of testing modems & DTEs to determine line or equipment fault where the device is disconnected from the telephone line, and a signal is looped out through the receive side
API	application programming interface - A set of routines that an application uses to request and carry out lower-level services performed by a computer's operating system. These routines usually carry out maintenance tasks such as managing files and displaying information.
APIPA	Automatic Private IP Addressing - A feature of Windows XP: TCP/IP that automatically configures a unique IP address from the range 169.254.0.1 through 169.254.255.254 and a subnet mask of 255.255.0.0 when the TCP/IP protocol is configured for dynamic addressing and a Dynamic Host Configuration Protocol (DHCP) is not available
AppleTalk	Apple Computer network architecture and network protocols. A network that has Macintosh clients and a computer running Windows 2000 Server or Windows NT Server with Services for Macintosh functions as an AppleTalk network
AppleTalk Phase 2	The extended AppleTalk Internet model designed by Apple Computer that supports multiple zones within a network and extended addressing capacity
ASCII	American Standard Code for Information Interchange - A standard coding scheme that assigns numeric values to letters, punctuation characters, control characters, and numbers to achieve compatibility among different computers and peripheral devices ASCII uses designated 7-bit or 8-bit number combinations to represent either 128 or 256 possible characters. Standard ASCII uses 7 bits to represent all uppercase and lowercase letters, the numbers 0 through 9, punctuation marks, and special control characters used in U.S. English. Most current x86-based systems support the use of extended (or "high") ASCII. Extended ASCII allows the eighth bit of each character to identify an additional 128 special symbol characters, foreign-language letters, and graphic symbols
ARP	Address Resolution Protocol - A method of finding the Ethernet address of a host from its Internet address. The sender broadcasts an ARP packet containing the Internet address of a host and waits for it (or another host) to send back its Ethernet address. Each host maintains a cache of address translations to reduce delay and loading. ARP allows the Internet address to be independent of the Ethernet address, but this protocol works only if all hosts support it In TCP/IP, ARP is a protocol that uses broadcast traffic on the local network to resolve a logically assigned IP address to its physical hardware or media access control layer address In ATM, ARP is used two different ways. For classical IP over ATM, ARP is used to resolve addresses to ATM hardware addresses. For ATM LAN emulation, ARP is used to resolve Ethernet/802.3 or Token Ring addresses to ATM hardware addresses
ASP	Application Service Provider
A.s.h.T.R.a.y	Receptacle used for depositing spent cigarettes & associated ash deposits - also matches
Assistive Technology Program	A service that provides recommendations for technology that can help people with disabilities
Asynchronous communication	A form of data transmission: info is sent & received, one character at a time, at irregular intervals. Start & stop bits 'tell' the receiving modem when data bits begin & end
ATM	Asynchronous Transfer Mode - A high-speed connection-oriented protocol that packs digital information into 53-byte cells that can be switched quickly between logical connections on a network. The cells switch throughout a network over virtual circuit
Authentication	The process that validates a user's login information on a network operating system or a multiuser system. Authentication usually involves resolving user names & passwords to an authorised user list
authoritative	describes a DNS server hosting a zone, or a zone containing a name or record. When a DNS server is configured to host a zone, it is said to be authoritative for names that do exist or could exist within that zone. A DNS server is allowed to respond authoritatively to queries for domain names for which it is authoritative. A zone is said to be authoritative for a name if the name exists or could exist within a zone, and it is said to be authoritative for a record if the owner name of the record exists or could exist within a zone
authoritative restore	In Backup, a type of restore operation performed on an Active Directory domain controller in which the objects in the restored directory are treated as authoritative, replacing (through replication) all existing copies of those objects. Authoritative restore is applicable only to replicated system state data such as Active Directory data and File Replication service data. Use the Ntdsutil.exe utility to perform an authoritative restore
Average Cell Rate	Maximum sustainable or average rate (Cells/second) for sending cells to the network. Average Cell Rate specifies bandwidth utilization. This value must always be less than or equal to Peak Cell Rate
AXFR	full zone transfer - The standard query type supported by all DNS servers to update and synchronize zone data when the zone has been changed. When a DNS query is made using AXFR as the specified query type, the entire zone is transferred as the response
B
B-channel	aka bearer channel: single channel of ISDN that is used to carry either voice or data. ISDN Basic Rate Interface (BRI) has 2 B-channels. ISDN Primary Rate Interface (PRI) in North America has 23 B-channels. ISDN30e Primary Rate Interface (PRI) in Europe has 30 B-channels
B-ISDN	broadband integrated services digital network - An ITU-T communication standard for high-speed networking that provides new services, including voice, video, and data on the same network
Back plane	A high-speed communications line to which individual components are connected.
Backbone	The part of a network that serves as a communications highway for LAN-to-LAN traffic. LANs are connected to the backbone through bridges and routers.
Bandwidth	Amount of data that can be transmitted over a given time period: The bandwidth determines the rate at which information can be transmitted over a computer channel, communications line, or bus. The greater the bandwidth, the greater number of megabits can be transmitted per second: An analog telephone line allows a bandwidth of 3,000 hertz (Hz), the difference between the lowest (300 Hz) and highest (3,300 Hz) frequencies it can carry. In digital communications, bandwidth is expressed in bits per second (bps)
Bandwidth on demand	A cost-saving feature that allows a device to establish a communications link to the central LAN only when bandwidth is required to transfer data. Bandwidth on demand is suitable for high-speed connection of voice, data, and video services
BAP	Bandwidth Allocation Protocol - A PPP control protocol that is used on a multiprocessing connection to dynamically add and remove links
base priority - processor	A precedence ranking that determines the order in which the threads of a process are scheduled for the processor. Use Task Manager to view and change base priorities
base priority - Message Queuing	a property that specifies the queue's priority in a public queue. You can set the base priority from -32,768 to 32,767; the default priority is 0. Private queues do not support base priority. Message Queuing routes and delivers messages first by base priority, then by message priority
batch program	aka batch files - An ASCII (unformatted text) file that contains one or more operating system commands. A batch program's file name has a .cmd or .bat extension. When you type the file name at the command prompt, or when the batch program is run from another program, its commands are processed sequentially
baud rate	The speed at which a modem communicates. Baud rate refers to the number of times the condition of the line changes. This is equal to bits per second only if each signal corresponds to one bit of transmitted data. Modems must operate at the same baud rate in order to communicate with each other. If the baud rate of one modem is set higher than that of the other, the faster modem usually alters its baud rate to match that of the slower modem
BDC	backup domain controller - In Windows NT Server 4.0 or earlier, a computer running Windows NT Server that receives a copy of the domain's directory database (which contains all account and security policy information for the domain). The copy is synchronized periodically and automatically with the master copy on the primary domain controller (PDC). BDCs also authenticate user logon information and can be promoted to function as PDCs as needed. Multiple BDCs can exist in a domain. Windows NT 3.51 and 4.0 BDCs can participate in a Windows 2000 domain when the domain is configured in mixed mode
BPDU	Bridge Protocol Data Unit - Data messages exchanged across switches in an extended LAN with a spanning tree protocol topology. BPDU packets assure that data arrives at the intended destination. These packets contain information on addresses, costs, ports, and priorities. Network loop detection involves exchanging BPDU messages across bridges. Loop deletion entails placing redundant switch ports in a backup (blocked) state and shutting down selected bridge interfaces
BGP	Border Gateway Protocol - A routing protocol that interconnects organisational networks and evaluates each of the possible routes to find the best one.
BIND	Berkeley Internet Name Domain - An implementation of DNS written and ported to most available versions of the UNIX operating system. The Internet Software Consortium maintains the BIND software
BIND boot file	Configuration file used by Domain Name System (DNS) servers running under versions of the Berkeley Internet Name Domain (BIND) software implementation. The BIND boot file is a text file, Named.boot, where individual lines in the file list boot directives used to start a service when the DNS server is started. By default, Microsoft DNS servers use DNS service parameters stored in the registry, but they allow the use of a BIND boot file as an alternative for reading boot configuration settings
bindery	A database in Novell NetWare 3.x that contains organizational and security information about users and groups
BIOS	basic input/output system - On x86-based computers, the set of essential software routines that test hardware at startup, start the operating system, and support the transfer of data among hardware devices. The BIOS is stored in read-only memory (ROM) so that it can be executed when a PC is powered up. Although critical to performance, the BIOS is usually invisible to users
Bit	aka Binary Digit - The smallest unit of data that a computer processes. A bit is either ON or OFF, representing a 1 or a 0. A group of 8 bits makes up a byte, which can represent many types of information, such as a letter of the alphabet, a decimal digit, or other character
boot files	The system files needed to start Windows. The boot files include Ntldr and Ntdetect.com
Boot Logging	A process in which a computer that is starting (booting) creates a log file that records the loading of each device and service. The log file is called Ntbtlog.txt, and it is saved in the system root directory
boot partition	The partition that contains the Windows operating system and its support files. The boot partition can be, but does not have to be, the same as the system partition
boot volume	The volume that contains the Windows operating system and its support files. The boot volume can be, but does not have to be, the same as the system volume
BOOTP extensions	A set of optional information types defined originally in RFC 1497 for use with BOOTP service and later supported by DHCP. In DHCP, these extensions form the legacy core set of client parameters available and supported by most standard DHCP and BOOTP servers
BOOTP	bootstrap protocol - protocol used primarily on TCP/IP networks to configure diskless workstations. RFCs 951 and 1542 define this protocol. DHCP is a later boot configuration protocol that uses this protocol. The Microsoft DHCP service provides limited support for BOOTP service
boot	The process of starting or resetting a computer. When first turned on (cold boot) or reset (warm boot), the computer runs the software that loads and starts the computer's operating system, which prepares it for use
BPDU	Bridge Protocol Data Unit - A data broadcast that informs each attached bridge of the configuration and operating state of every other attached bridge.
Bps	Bits Per Second - The rate at which data is sent over a communication line [ie modem] during a data-transfer operation
Bridge	A device that connects two LAN segments [or separate LANs] together at low protocol levels. These LAN segments may be of similar or dissimilar types, such as Ethernet and Token Ring. Inserting a bridge into a network segments the network. The bridge improves performance by keeping traffic contained within bridge segments by dividing the LAN into smaller units and keeping a list of service nodes on either side of it
Bridge Loop	Path that links one network segment to another. The spanning tree protocol avoids bridge loops
Bridge Priority	Determines which bridge is the root bridge
broadband	communications systems in which the medium of transmission (such as a wire or fiber-optic cable) carries multiple messages at a time, each message modulated on its own carrier frequency by a modem
broadband connection	A high-speed connection. Broadband connections are typically 256 kilobytes per second (KBps) or faster. Broadband includes DSL and cable modem service
Broadcast	A packet delivery system that transmits a copy of a given packet to all attached hosts. Broadcast is a special form of multicast in which the subset of machines to receive the packet consists of the entire set [ie destined for all hosts on a particular network segment]
buffer	A region of RAM reserved for use with data that is temporarily held while waiting to be transferred between two locations, such as between an application's data area and an input/output device
built-in groups	The default security groups installed with the operating system. Built-in groups have been granted useful collections of rights and built-in abilities. In most cases, built-in groups provide all the capabilities needed by a particular user. eg, if a domain user account belongs to the built-in Administrators group, logging on with that account gives a user administrative capabilities over the domain and the domain servers. To provide a needed set of capabilities to a user account, assign it to the appropriate built-in group
Burst Size (Cells)	Maximum number of cells that the user can send at peak rate in a burst
bus	A communication line used for data transfer among the components of a computer system. A bus essentially allows different parts of the system to share data. eg, a bus connects the disk-drive controller, memory, and input/output ports to the microprocessor
Byte	aka Octet - Eight bits of information
bytes	A unit of data that typically holds a single character, such as a letter, a digit, or a punctuation mark. Some single characters can take up more than one byte
C
Cable modem	A device that enables a broadband connection to the www by using cable television infrastructure. maximum throughput of 10 megabits per second (Mbps)
cache	For DNS and WINS, a local information store of resource records for recently resolved names of remote hosts. Typically, the cache is built dynamically as the computer queries and resolves names. It also helps optimize the time required to resolve queried names
cache file	aka root hints file - A file used by the Domain Name System (DNS) server to preload its names cache when service is started. Also known as the root hints file because DNS uses resource records stored in this file to help locate root servers that provide referral to authoritative servers for remote names. For Windows DNS servers, the cache file is named Cache.dns and is located in the %SystemRoot%\System32\Dns folder
caching	the temporay storing of recently used data values in a pool in memory for quicker access. For DNS, typically the ability of the DNS server to store information learned about the DNS namespace during the resolution of DNS queries. (eg, the DNS server can cache DNS records received from other DNS servers.) Caching is also available through the DNS Client service as a way for DNS clients to keep a cache of information learned during recent queries
caching resolver	client-side DNS name resolution service that performs caching of recently learned DNS domain name information. The caching resolver service provides system-wide access to DNS-aware programs for resource records obtained from DNS servers during processing of name queries. Cached data is used for a limited period of time and aged according to the active Time-to-Live (TTL) value. You can set the TTL individually for each resource record (RR). Otherwise, it defaults to the minimum TTL set in the SOA RR for the zone
canonical name	An object's distinguished name presented with the root first and without the LDAP attribute tags (such as: CN=, DC=). The segments of the name are delimited with forward slashes (/). eg CN=MyDocuments, OU=MyOU,DC=Microsoft,DC=Com is microsoft.com/MyOU/MyDocuments
CAP	Carrierless Amplitude and Phase Modulation - Modulation method used by modems and DSL equipment. Based on QAM. Signals modulate two wideband signals using passband modulation. CAP permits two to nine bits per frequency cycle
Carrier	A company that provides communication circuits. Also, a signal that can be modulated or impressed with a second information-carrying signal. The carrier itself conveys no information until it is altered. Changes to the amplitude, frequency or phase modulation convey the information.
Carrier wave	- Periodic waveform. A carrier may be modulated or unmodulated. It may also be continuous or switched. Typically, modems modulate the carrier wave with a data signal. Modulation represents the data signal by impressing a variation on some characteristic of the carrier wave. [ie a circuit may represent the signal as a proportional shift in carrier amplitude, frequency, or phase]. Demodulation (detection) eliminates the carrier wave and reproduces the signal. The carrier frequency must be significantly greater than the signal frequency. A modem may simultaneously apply more than one signal and more than one modulation method to the same carrier. The modulation method may suppress the carrier before transmission. In that case, the receiver must reinsert the carrier before demodulation can occur
cascading hubs	A network configuration in which hubs are connected to other hubs
CBR	Constant Bit Rate - an ATM service type that supports real-time applications with a fixed bandwidth. These applications, [eg a voice or video stream that require little or no cell loss and rigorous timing] produce data at regular intervals. The user can specify how much bandwidth to reserve
CCP	Compression Control Protocol - A protocol used in the negotiation process in a PPP connection. CCP is one type of Network Control Protocol (NCP). NCPs are used to establish & configure different network protocol parameters for IP, IPX, and NetBEUI
CD	Carrier Detect - A signal sent from a modem to the PC to indicate that the modem is on-line
CD	Compact Disc
CDMA	Code Division Multiple Access
CD-R	Recordable compact disc. Data can be burned to the CD but not erased
CD-RW	Rewritable compact disc. Data can be copied to the CD on more than one occasion and can be erased [ie the disc is re-useable]
CDVT	(Cells) - Parameter that constrains the number of cells that the user can send to the network at the maximum line rate
Central office	The facility [ie the local exchange] owned by the ISDN service provider that contains the ISDN switching equipment needed to provide ISDN service to the customer premises. [also applies to analogue trunks]
certificate	A digital document that is commonly used for authentication & secure exchange of information on open networks, such as the www, extranets & intranets. A certificate securely binds a public key to the entity that holds the corresponding private key. Certificates are digitally signed by the issuing certification authority and can be issued for a user, a computer, or a service. The most widely accepted format for certificates is defined by the ITU-T X.509 version 3 international standard
CA	certification authority - An entity responsible for establishing & vouching for the authenticity of public keys belonging to users (end entities) or other certification authorities. Activities of a certification authority can include binding public keys to distinguished names through signed certificates, managing certificate serial numbers, and certificate revocation
certification hierarchy	A model of trust for certificates in which certification paths are created by means of the establishment of parent-child relationships between certification authorities
certification path	An unbroken chain of trust, consisting of certificates from trusted certificate authorities, from a specific certificate to the root certification authority in a certification hierarchy
CF Card	CompactFlash Card - memory storage device for palm-sized & handheld PCs, which don't have HDD
Channel	A connecting path that carries information from a sending device to a receiving device. A channel can refer to a physical medium or to a specific frequency within a larger channel. eg A single ISDN2e Basic Rate Interface (BRI) connection has one physical connection but two channels for exchanging information between devices. This is called a bearer channel, implying a channel that carries information
child object	An object that resides in another object. A child object implies relation. eg, a file is a child object that resides in a folder, which is the parent object
CHAP	Challenge Handshake Authentication Protocol - An authentication protocol in which the authenticator sends a challenge message to verify the identity of a remote user. CAHP is documented in RFC 1994, it uses the industry-standard Message Digest 5 (MD5) one-way encryption scheme to hash the response to a challenge issued by the remote access server.PPP calls must go through CHAP. Microsoft has created a Windows-specific variant of CHAP called MS-CHAP
Class A IP address	A unicast IP address that ranges from 1.0.0.1 through 126.255.255.254. The first octet indicates the network, and the last three octets indicate the host on the network
Class B IP address	A unicast IP address that ranges from 128.0.0.1 through 191.255.255.254. The first two octets indicate the network, and the last two octets indicate the host on the network
Class C IP address	A unicast IP address that ranges from 192.0.0.1 to 223.255.255.254. The first three octets indicate the network, and the last octet indicates the host on the network. Network Load Balancing provides optional session support for Class C IP addresses (in addition to support for single IP addresses) to accommodate clients that make use of multiple proxy servers at the client site
Classfull addressing	A state in which an IP address space is divided into three predefined categories - Class A (8-bit), Class B (16-bit), and Class C (24-bit)
Classless addressing	A state in which an IP address space is divided into arbitrary sizes rather than the standard 8-bit, 16-bit, and 24-bit networks associated with classfull addressing.
client	Any computer or program connecting to, or requesting the services of, another computer or program. Client can also refer to the software that enables the computer or program to establish the connection
client	LAN or www - a computer that uses shared network resources provided by another computer (a server)
client request	A service request from a client computer to a server computer or, for Network Load Balancing, a cluster of computers. Network Load Balancing forwards each client request to a specific host within the cluster according to the system administrator's load-balancing policy
Client/server	A computer on a LAN that provides information or applications. The client-server splits the workload between desktop PCs (workstations) and one or larger computers (servers) connected on a LAN
CLIP	classical IP over ATM - A proposed Internet standard, described in RFC 2225, that allows IP communication directly on the ATM layer, bypassing an additional protocol (such as Ethernet or Token Ring) in the protocol stack
CLIP	Calling Line Identification Presentation - in telecomms, presentation of the callers CLI
ClipBook Server	A system service that supports ClipBook Viewer, which allows pages to be seen by remote ClipBooks
Cluster	aka allocation unit - The smallest amount of disk space that can be allocated to hold a file. All file systems used by Windows organize hard disks based on allocation units. The smaller the allocation unit size, the more efficiently a disk stores information. If you do not specify an allocation unit size when formatting the disk, Windows picks default sizes based on the size of the volume. These default sizes are selected to reduce the amount of space that is lost and the amount of fragmentation on the volume
cluster	computer networking: a group of independent computers that work together to provide a common set of services and present a single-system image to clients. The use of a cluster enhances the availability of the services and the scalability and manageability of the operating system that provides the services
cluster adapter	The adapter that, when using multiple network adapters in each host of a Network Load Balancing cluster, handles the network traffic for cluster operations (the traffic for all hosts in the cluster). This adapter is programmed with the host's cluster IP address
Cluster Administrator	An application that is used to configure a cluster and its nodes, groups, and resources. Cluster Administrator can run on any member of the trusted domain regardless of whether the computer is a cluster node
Cluster Administrator extension	A software component that implements the Cluster Administrator extension application programming interface (API) for allowing Cluster Administrator to configure a new resource type
Cluster API	A collection of functions that are implemented by the cluster software and used by a cluster-aware client or server application, a cluster management application, or a Resource DLL. The Cluster API is used to manage the cluster, cluster objects, and the cluster database
cluster disk	A disk on a shared bus connected to the cluster nodes, which all the cluster nodes can access (though not at the same time)
Cluster service	The essential software component that controls all aspects of server cluster operation and manages the cluster database. Each node in a server cluster runs one instance of the Cluster service
cluster-aware application	An application that can run on a cluster node and that can be managed as a cluster resource. Cluster-aware applications use the Cluster API to receive status and notification information from the server cluster
cluster-unaware application	An application that can run on a cluster node and be managed as a cluster resource but that does not support the Cluster API
Cluster.exe	An alternative to using Cluster Administrator to administer clusters from the command prompt. You can also call Cluster.exe from command scripts to automate many cluster administration tasks
CMOS	Complementary Metal Oxide Semiconductor: low power logic circuit: a specific type of semiconductor technology that requires very little power. The term has been popularized to mean a small storage area where the system keeps track of certain hardware parameters, such as HDD size, number of serial ports etc. aka Setup RAM.
CODEC	Coder/Decoder - hardware that can convert audio or video signals between analog and digital forms (coder/decoder); hardware or software that can compress and uncompress audio or video data (compression/decompression); or the combination of coder/decoder and compression/decompression. Generally, a codec compresses uncompressed digital data so that the data uses less memory.
COM port	The device name used to denote a serial communications port in DOS - a port that allows asynchronous communication of one byte at a time
community name	A name used to group SNMP hosts. This name is placed in SNMP messages sent between SNMP-managed devices such as Windows 2000-based server computers and SNMP management stations. Typically, all hosts belong to Public, which is the standard name for a common community of all SNMP hosts
Compression	A technique that reduces the number of bits needed to represent information in data transmission or storage. Compression also saves memory and bandwidth, and can increase the capacity of low-speed WAN links at minimal cost
Console	Terminals used to monitor & control a PC or network. The console consists of an RS-232 compatible terminal port, together with compatible software for a VT100 (asynchronous) terminal
console tree	The left pane in a Microsoft Management Console (MMC) that displays the items contained in the console. By default it is the left pane of a console window, but it can be hidden. The items in the console tree and their hierarchical organization determine the capabilities of a console
CNAME	canonical resource record - A resource record used to map an alternate alias name to a primary canonical DNS domain name used in the zone
convergence	The process of stabilizing a system after changes occur in the network. For routing, if a route becomes unavailable, routers send update messages throughout the internetwork, reestablishing information about preferred routes
convergence	Network Load Balancing - a process by which hosts exchange messages to determine a new, consistent state of the cluster and to elect the host with the highest host priority, known as the default host. During convergence, a new load distribution is determined for hosts that share the handling of network traffic for specific TCP or UDP ports
count limit	For Process Control, the maximum number of active processes in a process group. You can configure this in the Process Control snap-in
CRC	Cyclical Redundancy Check - An error-checking measure used to ensure the accuracy of transmitting data. The transmitted message is a small integer value computed from a sequence of octets. This value is used to detect errors that result when the sequence of octets is transmitted from one machine to another
CRC errors	Errors caused by the failure of a cyclic redundancy check. A CRC error indicates that one or more characters in the data packet received were found garbled on arrival
CRL	certificate revocation list - A document maintained & published by a certification authority that lists certificates that have been revoked
CRL distribution point	An optional extension in an X.509v3 certificate that identifies how information is obtained. Also, a directory entry or other distribution source for certificate revocation lists
CryptoAPI	An application programming interface (API) that is provided as part of Microsoft Windows. CryptoAPI provides a set of functions that allow applications to encrypt or digitally sign data in a flexible manner while providing protection for the user's sensitive private key data. Actual cryptographic operations are performed by independent modules known as cryptographic service providers (CSPs)
CSID	called subscriber ID string - A string specifying the called subscriber ID transmitted by the receiving fax machine when receiving an inbound fax. This string is usually a combination of the fax or telephone number and the business name
CSMA/CD	Carrier Sense Multiple Access With Collision Detection - A method of getting onto and off of a LAN. Multiple workstations access a common transmission medium by listening until no signals are detected, then transmitting and checking to see if more than one signal is present. IEEE 802.3 and Ethernet LANs are based on the CSMA/CD standard transmission method
CSP	cryptographic service provider - code that performs authentication, encoding & encryption services that Windows-based applications access through the CryptoAPI. A CSP is responsible for creating keys, destroying them, and using them to perform cryptographic operations. Each CSP provides a different implementation of the CryptoAPI. Some provide stronger cryptographic algorithms, while others contain hardware components, such as smart cards
CTL	certificate trust list - A signed list of root certification authority certificates that an administrator considers reputable for designated purposes, such as client authentication or secure e-mail
CTS	Clear To Send - A hardware signal defined by the RS232C standard that indicates that the transmission can proceed
Cycle	One half of a periodic wave. ie a sinewave includes one positive and one negative cycle
D
D-channel	aka data channel: separate channel of ISDN used for ISDN signaling. For ISDN Basic Rate Interface (BRI), the D-channel is 16 kilobits per second (Kbps). For ISDN Primary Rate Interface (PRI), the D-channel is 64 Kbps
DACL	discretionary access control list - The part of an object's security descriptor that grants or denies specific users and groups permission to access the object. Only the owner of an object can change permissions granted or denied in a DACL
Data Compression	The coding of data to save storage space or transmission time. Although data is already coded in digital form for computer processing, it can often be coded more efficiently (using fewer bits). There are many compression algorithms and utilities. Compressed data must be decompressed before it can be used
Data encryption	A security procedure in which messages are enciphered in secret code so that only the intended receiver can read them.
datagram	One packet, or unit, of information that includes relevant delivery information, such as the destination address, that is sent through a packet-switching network
data-overrun error	A state in which the sending computer is transmitting characters faster than the receiving computer can accommodate them. If this problem persists, reduce the bps rate
data packet	A unit of information transmitted as a whole from one device to another on a network
DCE	Data Communications Equipment - One of two types of hardware connected by an RS-232-C serial connection, the other being a Data Terminal Equipment (DTE) device. A DCE is an intermediary device that often transforms input from a DTE before sending it to a recipient. A modem, for example, is a DCE that modulates data from a microcomputer (DTE) and sends it along a telephone connection
DDE	dynamic data exchange - A form of interprocess communication (IPC) implemented in the Microsoft Windows family of operating systems. Two or more programs that support dynamic data exchange (DDE) can exchange information and commands
DDR (memory)	Double data Rate Synchronous - evolutionary technology derived from SDRAM
DLL	dynamic-link library - operating system feature that allows executable routines (generally serving a specific function or set of functions) to be stored separately as files with .dll extensions. These routines are loaded only when needed by the program that calls them
dead-letter queue	Message Queuing, a queue that stores nontransactional messages that are undeliverable or expired. These queues store failed messages on the computer on which the message expired. Messages in these queues are written to disk and are therefore recoverable
dedicated adapter	The network adapter that, when using multiple network adapters in each host of a Network Load Balancing cluster, handles network traffic not related to cluster operations (the traffic for individual hosts on the network). This adapter is programmed with the host's dedicated IP address
dedicated circuit	A telecommunications channel leased between 2 or more service points within one exchange or between different exchanges, usually at a monthly rate. aka Leased line or a private line
default gateway	the IP address of an IP router. the default gateway creates a default route in the IP routing table
default host	The default host handles all the network traffic for TCP & UDP ports that are not covered by port rules
default network	Macintosh - the physical network on which the processes of a server reside as nodes and on which the server appears to users. The default network of the server must be one to which that server is attached. Only servers on AppleTalk Phase 2 internets have default networks
default zone	The zone to which all Macintosh clients on the network are assigned by default
DEL	Direct [analogue] exchange line
delegation	For DNS, a name service record in the parent zone that lists the name server authoritative for the delegated zone
delegation	The ability to assign responsibility for management and administration of a portion of the namespace to another user, group, or organization
denial-of-service attack	An attack in which an attacker exploits a weakness or a design limitation of a network service to overload or halt the service, so that the service is not available for use. This type of attack is typically launched to prevent other users from using a network service such as a Web server or a file server
dependency	A relationship of reliance between two resources that makes it necessary for them to run in the same group on the same node. eg, an application is dependent on the disks that contain its data resources
dependency tree	A diagram for visualizing the dependency relationships between resources
dependent client	Message Queuing - a computer that requires synchronous access to a Message Queuing server to perform all standard message queuing operations, such as sending and receiving messages and creating queues
DES	Data Encryption Standard - A NIST-standard encryption technique that scrambles data into an unbreakable code for public transmission. DES uses a binary number as an encryption key with 72 quadrillion possible combinations
descendent key	All the subkeys that appear when a key in the registry is expanded. A descendent key is the same as a subkey
desired zone	The zone in which AppleTalk network integration appears on the network
destination document	The document into which a package or a linked or embedded object is being inserted. For an embedded object, aka container document
device conflict	A conflict that occurs when the same system resources have been allocated to two or more devices. System resources include interrupt request (IRQ) lines, direct memory access (DMA) channels, input/output (I/O) ports, and memory addresses
DFS	Distributed File System
DFS link	An element in the Distributed File System (DFS) namespace that lies below the root and maps to one or more targets, each of which corresponds to a shared folder or another DFS root
DFS root	The starting point of the Distributed File System (DFS) namespace. The root is often used to refer to the namespace as a whole. A root maps to one or more root targets, each of which corresponds to a shared folder on a server
DFS topology	The overall logical hierarchy of the Distributed File System (DFS), including elements such as roots, links, shared folders, and replica sets, as depicted in the DFS administrative console. This is not to be confused with the DFS namespace, which is the logical view of shared resources seen by users
DHCP	Dynamic Host Configuration Protocol - Protocol for automatic TCP/IP configurations [ie issues IP addresses for a user - a pc]. DHCP provides static and dynamic address allocation and management A TCP/IP service protocol that offers dynamic leased configuration of host IP addresses and distributes other configuration parameters to eligible network clients. DHCP provides safe, reliable, and simple TCP/IP network configuration, prevents address conflicts, and helps conserve the use of client IP addresses on the network. DHCP uses a client/server model where the DHCP server maintains centralized management of IP addresses that are used on the network. DHCP-supporting clients can then request and obtain lease of an IP address from a DHCP server as part of their network boot process
DHCP client	A network-enabled device [eg PC] that can communicate with a DHCP server to obtain a dynamic leased IP configuration and related optional parameters
DHCP option	Pre-defined address configuration parameters assigned to clients by a DHCP service. Parameters are defined in Request for Comments (RFC) 1542
DHCP Relay	When a DHCP server is on a different LAN than the node broadcasting for DHCP service, the DHCP broadcast request must be forwarded across the router/WAN to a subnet where a DHCP server resides. To assure receipt of an IP address that corresponds to this subnet, the router must use a DHCP relay. The router needs to know the IP address of the DHCP server. With this address, the router can direct the request to the appropriate DHCP server
DHCP service resource	A resource type that provides DHCP services from a cluster
DHCP server	A computer running the Microsoft DHCP service that offers dynamic configuration of IP addresses and related information to DHCP-enabled clients.
DHCP/BOOTP Relay Agent	The agent program or component responsible for relaying DHCP & BOOTP broadcast messages between a DHCP server and a client across an IP router. A DHCP relay agent supports DHCP/BOOTP message relay as defined in RFCs 1541 and 2131. The DHCP Relay Agent service is managed using the Routing and Remote Access service
dial-up connection	The connection to a network or ISP using a device that uses the PSTN. This includes modems with a standard phone line, ISDN cards with high-speed ISDN lines, or X.25 networks
differential backup	A backup that copies files created or changed since the last normal or incremental backup. It does not mark files as having been backed up (in other words, the archive attribute is not cleared). If you are performing a combination of normal and differential backups, restoring files and folders requires that you have the last normal as well as the last differential backup
differential data	Saved copies of changed data that can be applied to an original volume to generate a volume shadow copy
direct cable connection	A link between the I/O ports of two computers created with a single cable rather than a modem or other interfacing devices. In most cases, a direct cable connection is made with a null modem cable
Direct routing	The transmission of a datagram from one machine directly to another
directory partition	A contiguous subtree of the directory that forms a unit of replication. A given replica is always a replica of some directory partition. The directory always has at least three directory partitions: The schema, which defines the object classes and attributes contained in Active Directory. The configuration, which identifies the domain controllers, replication topology and other related information about the domain controllers within a specific implementation of Active Directory. One or more domains that contain the actual directory object data. A domain controller always stores the partitions for the schema, configuration, and its own (and no other) domain. The schema and configuration are replicated to every domain controller in the domain tree or forest. The domain is replicated only to domain controllers for that domain. A subset of the attributes for all domain objects is replicated to the global catalog
directory service	Both the directory information source and the service that make the information available and usable. A directory service enables the user to find an object given any one of its attributes
distribution group	A group that is used solely for e-mail distribution and that is not security-enabled. Distribution groups cannot be listed in discretionary access control lists (DACLs) used to define permissions on resources and objects. Distribution groups can be used only with e-mail applications (such as Microsoft Exchange) to send e-mail to collections of users. If you do not need a group for security purposes, create a distribution group instead of a security group
DLC	Data Link Control - An address that uniquely identifies a node on a network. Every network adapter has a DLC address or DLC identifier (DLCI). Some network protocols, such as Ethernet and Token Ring, use DLC addresses exclusively. Other protocols, such as TCP/IP, use a logical address at the OSI Network layer to identify nodes. All network addresses must eventually be translated to DLC addresses. In TCP/IP networks, this translation is performed by the Address Resolution Protocol (ARP).
DLCI	DLC identifier
DMA	direct memory access - Memory access that does not involve the microprocessor. DMA is frequently used for data transfer directly between memory and a peripheral device such as a disk drive
DMT	Discrete Multi Tone - the most common DSL modulation method. DMT creates 256 channels across the usable frequency spectrum. Each channel measures 4.3125KHz wide. Dividing the spectrum into channels allows DMT to function well in spite of nearby AM radio transmitters. The DMT modulator and demodulator is the FFT (Fast Fourier Transform) algorithm. Inside each channel, the modulation technique is QAM. Within each channel, the number of bits per symbol may be independently selected. Independent selection allows a DMT modem to be rate adaptive. Both G.DMT and G.Lite use DMT
DNS	Domain Naming System - Mechanism used for translating Internet names of host computers into IP addresses [eg: www.sjgl.co.uk = 192.122.122.1] A hierarchical, distributed database that contains mappings of DNS domain names to various types of data, such as IP addresses. DNS enables the location of computers and services by user-friendly names, and it also enables the discovery of other information stored in the database
DNS Relay	DNS requests that the router forwards from a LAN node to a known DNS server. The router uses a DNS relay when the router functions as a NAPT device. The requests arrive at a DNS server over the WAN link. To function as a NAPT, the router requires DNS relay settings
DNS Server	A service that maintains information about a portion of the Domain Name System (DNS) database and responds to and resolves DNS queries. A computer running this service is also known as a DNS server
DNS suffix	For DNS, a character string that represents a domain name. The DNS suffix shows where a host is located relative to the DNS root, specifying a host?s location in the DNS hierarchy. Usually, DNS suffix describes the latter portion of a DNS name, following one or more of the first labels of a DNS name
Domain	A description of a single computer, a whole department, or a complete site, used for naming and administrative purposes
domain	A group of PCs that are part of a network and share a common directory database. A domain is administered as a unit with common rules and procedures. Each domain has a unique name. An Active Directory domain is a collection of computers defined by the administrator of a Windows network. These computers share a common directory database, security policies, and security relationships with other domains. An Active Directory domain provides access to the centralized user accounts and group accounts maintained by the domain administrator. An Active Directory forest is made up of one or more domains, each of which can span more than one physical location. A DNS domain is any tree or subtree within the DNS namespace. Although the names for DNS domains often correspond to Active Directory domains, DNS domains should not be confused with Active Directory domains
domain controller	a Windows computer running Active Directory that manages user access to a network, which includes logging on, authentication, and access to the directory and shared resources
domain controller locator	An algorithm that runs in the context of the Net Logon service and that finds domain controllers on a Windows 2000 network. Locator can find domain controllers by using DNS names (for IP/DNS-compatible computers) or by using NetBIOS names (for computers that are running Windows 3.x, Windows for Workgroups, Windows NT 3.5 or later, Windows 95, or Windows 98, or it can be used on a network where IP transport is not available)
domain DFS	An implementation of DFS in which DFS topological information is stored in Active Directory. Because this information is made available on multiple domain controllers in the domain, domain DFS provides fault-tolerance for any distributed file system in the domain
domain local group	A security or distribution group that can contain universal groups, global groups, and accounts from any domain in the domain tree or forest. A domain local group can also contain other domain local groups from its own domain. Rights and permissions can be assigned only at the domain containing the group
domain name	The name given by an administrator to a collection of networked computers that share a common directory. Part of the Domain Name System (DNS) naming structure, domain names consist of a sequence of name labels separated by periods
domain namespace	The database structure used by the Domain Name System (DNS)
domain naming master	The domain controller assigned to control the addition or removal of domains in the forest. At any time, there can be only one domain naming master in the forest
domain of origin	The parent DNS domain name that is used to root either a zone or a resource record within a zone. This name is joined to the end of unqualified or relative domain names to form a fully qualified domain name (FQDN) within the zone. In DNS Manager, the domain of origin will correspond to Zone name as it appears in the Add Zone Wizard or the name that appears in the Parent domain name field for any resource records created within the zone
domain tree	In DNS, the inverted hierarchical tree structure that is used to index domain names. Domain trees are similar in purpose and concept to the directory trees used by computer filing systems for disk storage. eg when numerous files are stored on disk, directories can be used to organize the files into logical collections. When a domain tree has one or more branches, each branch can organize domain names used in the namespace into logical collections
domain tree	In Active Directory, a hierarchical structure of one or more domains, connected by transitive, bidirectional trusts, that forms a contiguous namespace. Multiple domain trees may belong to the same forest
Dotted decimal notation	A method of representing an IP address in which the 32-bit binary number is broken down into four groups of eight bits each. In turn, each byte is converted from binary to decimal numbers separated by dots
Dpi	Dots per inch - measure of output device resolution and quality - ussually regarding printers
DRAM	Dynamic Random Access Memory
DSA	Digital Signature Algorithm
DSL	Digital Subscriber Line - A type of high-speed Internet connection using standard telephone wires. aka broadband
DSLAM