Glossary

This appendix provides a glossary of terms found throughout the TCPware for OpenVMS documentation set.

Glossary of Terms
access control list (ACL)	OpenVMS list containing access rights for users.
access restrictions	Restrictions on a TCP application's usage, either incoming or outgoing.
active open	Actively opens a connection. TCPDRIVER sends segments to establish a connection to the destination host and port number for an active open request. To establish a connection, a passive open must usually be pending on the destination host.
Address Resolution Protocol (ARP)	Protocol used to map internet addresses to physical hardware addresses used on Ethernet and FDDI. See Fiber Distributed Data Interface and Reverse Address Resolution Protocol.
Ancillary control process (ACP)	A process that acts as an interface between user software and an I/O driver. An ACP provides functions supplemental to those performed in the driver, such as file and directory management.
application program interface (API)	Programming interface to an application, such as the TCPware SNMP Extendible Agent MIB API, ACE/Client API for Token Authentication, or the interface between a terminal emulation program and the TES Client software.
ARPANET	First entity to implement TCP/IP. ARPANET is the DARPA internet that served as the backbone for TCP/IP research. TCP/IP was so successful in the ARPANET that DARPA designated TCP/IP as a networking standard.
Asynchronous Transfer Mode (ATM)	See Classical IP over ATM.
attributes data file (ADF)	Special file in the NFS Client that maintains the attributes for an OpenVMS data file. These files appear on the server as .$ADF$filename, although the client system cannot see them.
authenticator	The Kerberos protocol uses authenticators to prevent eavesdroppers from stealing a ticket. The client sends a new authenticator with each request for service from a server. An authenticator consists of the client's name, client's IP address, and a timestamp showing the current time.
automounting	Automatic and transparent mount in NFS that mounts a filesystem when accessing it.
Autonomous System (AS)	Set of routers under a single technical administration, using an internal protocol and common metrics to route packets within the AS, and an external protocol to route packets to other ASs. The NIC assigns AS numbers.
background mount	Attempts to mount a filesystem on the NFS client made at least once at varying intervals and specified number of retries. See  multicasting.
big-endian	Format for storage of binary data where the most-significant byte comes first. The Internet's standard byte order is big-endian. See little-endian and network byte order.
Border Gateway Protocol (BGP)	Exterior routing protocol used to exchange routing information between multiple transit Autonomous Systems (ASs) as well as between transit and stub ASs.
broadcasting	Packet delivery system that provides a copy of a given packet to all hosts attached to the network. For example: Ethernet and FDDI. See multicasting.
Classical IP over Asynchronous Transfer Mode (CLIP)	A way of sending IP datagrams over ATM protocol lines.
Classless Inter Domain Routing (CIDR)	Protocol developed in 1992 by the Internet Engineering Steering Group that eliminates address class distinctions and depends on address masks that fall on bit instead of byte boundaries. The strategy assigns blocks of Class C addresses to Internet providers and has the providers "subnet mask" the addresses in further units to organizations. This also sharply reduces the growth in routing tables in Internet routers beyond their manageable capacity.
client-server model	Concept used to describe the application layer protocols. The  process that initiates a service is the client (or user). The process that provides the service is the server. A client and a server can be on different hosts or on the same host.
cluster alias failover	System whereby a node in a VMScluster (the "alias") can accept incoming connection requests for a server if the servicing node goes down. Used primarily with the Network File System (NFS).
Compressed SLIP (CSLIP)	See Serial Line IP (SLIP).
connectionless service	Service that presents data complete with a destination address, and the network delivers it on a best-effort basis, independent of other data exchanged between the same pair of users. Examples include IP and UDP.
connection-oriented service	Service that implements a connection-setup procedure before it can exchange data between two users. Connection-oriented services or protocols provide data transfer that is reliable, ordered, full-duplex, and flow-controlled. TCP is a connection-oriented service.
data circuit-terminating equipment (DCE)	Term the X.25 protocol standards use that applies to switching equipment that forms a packet switched network to distinguish it from the computers or terminals that connect to the network.
datagram	Single message unit IP uses over an internet and consisting of protocol headers and data.
data terminal equipment (DTE)	Term X.25 protocol standards use that applies to computers and/or terminals, to distinguish them from the packet switching network to which they connect.
delta time	The delta time syntax is: dddd hh:mm:ss.cc • dddd is the number of days (0-9999); if less than one day, specify zero (0); follow with a blank space. • hh is the number of hours (0-23). • mm is the number of minutes (0-59) preceded by a colon (:). • ss is the number of seconds (0-59) preceded by a colon (:). • cc is the number of hundredths of a second (0-99) preceded by a period (.). You can truncate a delta time on the right. You can omit fields in the time format as long as you include the punctuation that separates the fields. You must specify the days field even if you omit all time fields.
domain namespace	Naming hierarchy. A domain name consists of a sequence of names (labels) separated by periods (.). The following are examples of domain names: NS.NASA.GOV            C.NYSER.NET              BBN.COM
Domain Name System (DNS)	System that allows access to a distributed, hierarchical database of internet addresses, hostnames, and other information throughout the Internet.
duress PIN	Special PIN to use if you are being compromised during the login process. Used with the token authentication system.
Dynamic Host Configuration Protocol (DHCP)	Protocol that centralizes and automates TCP/IP network configuration. The DHCP Server dynamically allocates IP addresses for hosts on the network from an available pool of addresses. In this way, new hosts or hosts that are frequently relocated can automatically get new IP addresses for a certain lease period. DHCP is an extension of the Internet Bootstrap Protocol (BOOTP).
dynamic routing	See Gateway Routing Daemon.
encryption	Transformation of plain text into unintelligible text.
EXPORT database	Database on the NFS server system that controls which filesystems the server is able to export to a client.
exporting	Making a network filesystem available to mount on a client system by listing it in the "export" database.
Exterior Gateway Protocol (EGP)	Exterior routing protocol that moves routing information between Autonomous Systems (ASs).
External Data Representation (XDR) Protocol	Standard that resolves differences of data representation between different operating systems and hardware architectures.
Fiber Distributed Data Interface (FDDI)	Set of ANSI/ISO standards that define a high-bandwidth (100 Mb/s) general-purpose LAN. It provides synchronous and asynchronous services between computers and peripheral equipment in a timed-token passing, dual ring of trees configuration.
File Sharing Services (FSS)	NetWare service that lets you access OpenVMS directories, files, and printers using DOS facilities.
File Transfer Protocol (FTP)	Application level protocol that allows a user on a client host to log in to a server host and perform file functions.
filename mapping	Process in NFS of mapping filenames between OpenVMS and UNIX so as to preserve the respective systems' file naming conventions.
filesystem	Method for recording, cataloging, and accessing files on a client or server system.
flat namespace	In flat namespace naming, a system selects object names from a single set of strings rather than a hierarchical organization of strings. The following hostnames are examples: ALPHA                         RESEARCH                         TULIP
Gateway Routing Daemon (GateD)	Manages multiple routing protocols, including the Routing Information Protocol (RIP), Local Network Protocol (HELLO), Router Discovery Protocol, Open Shortest Path First (OSPF) protocol, Exterior Gateway Protocol (EGP), and Border Gateway Protocol (BGP).
gateway	Device used to connect two or more networks to form an internet. A gateway also has an internet address for each connected network, and performs routing functions.
GROUP database	Database on the NFS Client that authorizes a client's group access to the remote host's filesystems. The database contains the group number and the VMS group identifier corresponding to the remote group identifier in the UNIX /etc/group file.
group ID (GID)	Group identification on the UNIX NFS host.
HELLO	Also called the Local Network Protocol, it is an interior protocol that uses delay as the deciding factor when selecting the best route. Delay is the round-trip time between source and destination. HELLO is not currently widely in use.
host	Unique, addressable entity that is part of an internet. A multiuser minicomputer and a terminal server are examples of hosts.
host byte order	Standard a host uses for storage and transmission of integers that specifies that either the least significant byte or most significant byte appears first. Sending machines must translate from their host or local machine integer representation to network byte order. Receiving machines must translate from network byte order to the local host or local machine representation. See big-endian and little-endian.
host equivalence files	Security access files on a Berkeley R Commands server host used to authorize access to services by other hosts or users. The files list hostnames (and, optionally, usernames) and indicate which remote hosts and users have equivalent access as local users. These include RHOSTS. and HOSTS.EQUIV files.
hostname	Name assigned to a host. These names are for user convenience and a system maps it to an internet address. Host names may either be from a flat namespace or the domain namespace. A hostname is a mnemonic given to a host for the purpose of identifying it. Because the TCP/IP protocols only understand internet address, they must "translate" these hostnames into internet addresses. TCPware supports two means for translating a hostname into an internet address (or vice versa); the HOSTS. file and Domain Name System (DNS). The HOSTS. file supports any naming conventions you wish to use. Typically, use of a HOSTS. file involves using a flat namespace. For larger networks and the Internet, systems now more commonly use the Domain Name System (DNS).
idempotency	Remote Procedure Call (RPC) jargon for performing an operation more than once with identical results and without causing any harm. For example, an NFS server receives a delete file request from a client, deletes the file, and sends a success reply, but the network loses the reply before it reaches the client. Because the client does not receive a reply, it sends the delete file request again. Rather then process the request again and send a false error message stating that the file does not exist, the server simply retransmits the original reply.
instance	In Kerberos authentication, identifies an instantiation of a principal name, such as the name of the system running a server.
internet	Network formed by connecting dissimilar hosts and networks with TCP/IP protocols. When capitalized (Internet), this term refers to the ARPANET, the DARPA internet that forms the backbone of internet research.
internet address	Unique 32-bit value assigned to each host in an internet. All internet communications with a particular host use its internet address. TCPDRIVER, UDPDRIVER, IPDRIVER, INETDRIVER, and BGDRIVER use internet addresses to identify a host on the network. Each host on the network assumes a unique internet address. Internet addresses are 32-bit values. Internet addresses are in reverse VAX byte order (the most significant byte of the internet address is in the least significant byte of the longword value).
Internet Control Message Protocol (ICMP)	Performs a function of IP by providing a communications facility for gateways and hosts.
Internet Message Access Protocol (IMAP)	Allows IMAP-compliant mail programs to access messages stored remotely as if the storage were local.
Internet Protocol (IP)	Basis of TCP/IP, providing the network interface and message routing services for the higher level protocols.
Internet Printing Protocol (IPP)	The IPP print symbiont is an OpenVMS print symbiont working with the OpenVMS printing subsystem to implement an IPP Client. It allows printing over a network to printers and servers that support the IPP v1.0 network printing protocol.
IP routing	Mechanism provided by IP to deliver datagrams from the source to the destination.
IP Security Option (IPSO)	U.S. Department of Defense standard for protecting datagrams over the network.
Kerberos	Authentication system for open systems and networks. Kerberos uses a set of encrypted keys and tickets for authentication. Kerberos provides network security by regulating user access to networking services.
Key Distribution Center (KDC)	An alternate name for the Kerberos Server.
layer	The TCP/IP protocol suite consists of three layers of services that rest on a layer of hardware.
little-endian	Format for storage of binary data in which the least significant byte comes first. The VAX, Alpha and I64 byte order is little-endian. See also big-endian.
load balancing	Also known as TCP/IP load balancing. The system whereby the server changes the preferred order of access to systems in a TCP/IP cluster in response to their observed load.
local area network (LAN)	Two or more hosts connected by the same communications medium. The hosts typically span a small geographic area such as a single room or building.
Management Information Base (MIB-II)	Most recent MIB version for the SNMP protocol. A collection of data residing on the SNMP agent host and organized into groups. Each piece of data within a group is a management object.
mask, address or network	32-bit internet address, where the network number is set to all bits one and the host number is set to all bits zero. Hosts and gateways use the network mask to route internet packets by extracting the network number of an internet address, and comparing the network number with their own routing information to determine if the packet is bound for a local address.
master file directory (MFD)	"Root" directory ([000000]) in OpenVMS that is the default mount point for an NFS filesystem.
mount	NFS protocol that provides file handles for server access and keeps track of mounts.
mount point	Point on the remote NFS directory tree that you are interested in mounting or the point on the local directory tree where the remote filesystem is "attached."
mounting	Process in NFS of "attaching" a server filesystem to the file structure of a client to make it accessible using the client's normal operating facilities.
multicasting	Special form of broadcasting that delivers copies of the packet to only a subset of all possible destinations. See broadcasting.
multiplexing	Transmission of a number of different messages simultaneously over a single circuit.
multithreading	Ability to service transactions from many clients simultaneously.
network	Element of an internet in which two or more hosts are connected with the same communications medium. A LAN is an example of an internet network element.
network byte order	Internet standard for transmission of integers that specifies most significant byte appears first. Sending machines must translate from the local integer representation to network byte order, and receiving machines must translate from network byte order to the local machine representation. Equivalent to big-endian. See little-endian.
Network Control Utility (NETCU)	TCPware's utility program system managers and operators use to configure and control networks that run TCPware.
Network File System (NFS)	Application layer protocol developed by Sun Microsystems, Inc. that provides access to a remote computer's files as if they were local files.
Network Information Center (NIC)	Central organization of a network with the authority to create network names and addresses. NIC.DDN.MIL is the specific Internet NIC that holds the authority to create root servers.
Network Lock Manager (NLM) and Status Monitor (NSM)	The way in which the Network File System (NFS) supports file locking. Many NFS client systems support file locking, even on the record and byte level, as long as the byte ranges do not overlap. File locking on the Server is multithreaded, where the Server can satisfy more than one lock request at a time. The NSM cooperates with other status monitors on the network to notify the NLM of any changes in system status (such as when a crash occurs).
Network Print Services (NPS)	NetWare service that lets OpenVMS users print their files on any printer connected to NetWare LANs.
Network Time Protocol (NTP)	Protocol that synchronizes timekeeping among a set of distributed time servers and clients.
NSLOOKUP	Utility that queries information from DNS servers, based on RFCs 1034 and 1035.
occluded mount	Action in NFS where a filesystem mounts on a subdirectory of an existing mount point so that previously visible subdirectories and files of the original mount are no longer visible.
ONC RPC Services	Software development tool with which programmers can build distributed applications on VAX computers.
Open Shortest Path First (OSPF) Protocol	Interior gateway protocol that distributes routing information between routers in a single Autonomous System (AS). OSPF chooses the least cost path as the best path.
overmounting	Action in NFS where a filesystem mounts on top of an existing mount point.
packet	Single message as it appears to the physical network.
packet filtering	Restricts the datagrams that an interface can receive.
Packet Switching Data Network (PSDN) and packet switching exchange (PSE)	A PSDN consists of widely separated packet switching exchanges (PSEs). PSEs connect through public or private telephone networks or leased lines. PSEs contain data circuit-terminating equipment (DCE).
Passcode	Combination of your PIN and the tokencode. Used with the token authentication system.
passive open	Passive open "listens" and waits for a request from a remote host to establish a connection. You can fully or partially specify passive opens. Use partially specified opens when you do not know the requesting host. Note that a passive open does not send requests to establish a connection until the system receives a request from another host.
pathname	Directory path in a remote NFS filesystem.
PCNFSD	NFS authentication server to allow remote printing over NFS.
PC-peer	Synchronized host in the Network Time Protocol (NTP), which is either a time server or client and is identified by a relative NTP strata number.
PIN	Your personal identification number and part of the token authentication system. The PIN consists of four to eight alphanumeric characters.
PING	Packet InterNet Groper, a utility that tells you whether a host is up and whether you can reach it. The PING utility uses the ICMP echo and echo reply messages.
Point-to-Point Protocol (PPP)	Protocol whereby you can send IP datagrams over serial links, including LAT or modem connections. PPP is an enhancement to the nonstandard Serial Line IP (SLIP) interface, providing self-contained error detection and automatically negotiated header compression. It also provides authentication through the Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP).
port and port number	Abstract point through which a datagram passes from the host layer to the application layer protocols. Port number is a number the network drivers use to name the ends of logical connections. Port numbers are 16-bit values. Some standard server port numbers are 21 for FTP, 23 for TELNET, and 25 for SMTP. Servers generally use the port numbers from 0 to 255. User port numbers start at 1024. Specify port numbers in normal VAX byte order, unless indicated otherwise.
Post Office Protocol Version 3 (POP3)	Multithreaded server that can handle up to 31 simultaneous client connections. POP3 does not perform any mail delivery functions but simply allows clients (mostly PCs) to retrieve new mail from local inboxes.
principal	Kerberos client and server names in the format name.instance@realm. For clients, name is the user's login name; for servers, name is the service name. See instance and realm.
print symbiont	Privileged process used to manage a queue of jobs sent to a local or remote printer.
Product Authorization Key (PAK)	HP's product licensing mechanism.
protocol	Standard that defines how computers on a network communicate with each other.
PROXY database	Database on the NFS client or server system that authorizes a client's access to the remote host's filesystems. The database contains the UNIX identity of its client, consisting of a UID and GID.
Quote-of-the-Day service (QUOTED)	TCP-based character generator service that listens for TCP connections on TCP port 17. Once you establish a connection, the service sends a short message. The service then throws away any data it receives and closes the connection.
realm	In Kerberos authentication, the name of a group of machines, such as those on a LAN, identifying the Kerberos administrative domain.
Record Management Services (RMS)	Set of operating system procedures called by programs to process files and records within files. Defines rules about how to store records in files.
Remote Compact Disk (RCD)	Utility that provides access to CD-ROM drives on remote TCP/IP systems.
Remote Copy Program (RCP)	UNIX-like command with which you can copy files over the network.
Remote Login Protocol	See TELNET.
Remote Magnetic Tape (RMT)	Utility that provides access to magnetic tape drives on remote TCP/IP systems.
Remote Procedure Call (RPC)	Set of protocols developed by Sun Microsystems, Inc. These protocols allow programs to invoke procedures on remote hosts as if the procedures were local. See ONC RPC Services.
Request for Comments (RFC)	Documents submitted to the Internet governing board to define  Internet standards.
resolver	A Domain Name System (DNS) client that communicates with a DNS server to resolve a host name and internet address. The client does not maintain a database. The client only sends queries; it does not answer them.
resource record	Entry in a Domain Name System (DNS) database files.
Reverse Address Resolution Protocol (RARP)	Protocol used to map the physical hardware addresses to the IP address (used on Ethernet and FDDI). Diskless machines use this protocol to find their IP addresses from the server.
rlogin	Remote login; a Berkeley UNIX system service that allows users of one machine to connect to other UNIX machines across the Internet and interacts as if their terminals were directly connected to the machines. The software passes information about the user's environment, such as terminal type, to the remote machine.
Router Discovery Protocol	IETF standard protocol used to inform hosts of the existence of routers without having hosts wiretap routing protocols such as RIP. Used in place of, or in addition to statically configured default routes in hosts.
Routing Information Protocol (RIP)	Distance-vector protocol for distributing routing information at the local network level of the Internet. In distance-vector routing, each router transmits destination addresses and costs to its neighbors.
Serial Line IP (SLIP)	A point-to-point protocol used when you need to route TCP/IP traffic over a serial line instead of an Ethernet cable. You most commonly use SLIP to connect systems on two Ethernet networks some distance apart. Compressed SLIP (CSLIP) is used to compress the TCP/IP headers only (and not the data) over the SLIP line.
server	Host providing a service in a relationship between two cooperating processes.
Simple Mail Transfer Protocol (SMTP)	Application layer protocol that provides an electronic mail facility to an internet.
Simple Network Management Protocol (SNMP)	Allows network management stations to obtain timely information about the network activities of OpenVMS server hosts. The information describes such things as routing, line status, the volume of network traffic, and error conditions.
sliding window	Characteristic of protocols that allow the sender to transmit up to n packets before an acknowledgment arrives. After the system receives an acknowledgment for the first packet, the sending protocol slides the packet window along the stream and sends another packet.
socket	Abstraction first provided by Berkeley BSD UNIX that allows a process to have access to the Internet. A process opens a socket, specifies the desired service (reliable stream delivery, datagram delivery, IP) connects the socket to a specified destination, and then sends or receives data.
Socket Library	Collection of VAX C (on VAX machines) and DEC C (on Alpha and I64 machines) subroutines that closely emulates the UNIX socket functions.
SSH	Abbreviation for Secure Shell. See Accessing Remote Systems with the Secure Shell (SSH) Utilities.
statelessness	Ability not to have to maintain information from a previous request to process a new one. The Network File System (NFS) is an example of a stateless operation.
stratum	Number for a peer in the Network Time Protocol (NTP) that identifies the relative hierarchy of the peer. Lower strata peers act as time servers while higher strata peers are clients who adjust their time clocks according to these servers. An Internet Time Server (ITS) on the network is assigned stratum 1 because it has radio-clock-generated time based on Universal Coordinated Time (UTC).
stream service	TCP service that transfers data in a continuous flow, without the use of markers to show the beginning or end of messages.
STREAM-LF file	Record structure OpenVMS uses where it views the file's records as a continuous stream of bytes delimited by a line feed (LF) character.
subnetwork (subnet)	Subdivision of a network used to provide a means to logically group hosts within a large network.
subnet mask	Thirty-two-bit internet address created by taking bits from the host number and using them to extend the network mask. Hosts and gateways local to a subnet use the subnet mask for local routing.
superuser	UNIX or NFS user having almost unlimited privileges. The superuser usually has a User ID (UID) of 0.
symbiont	Process that transfers record-oriented data to or from a device. For example, an output symbiont transfers data from disks to line printers. See print symbiont.
TALK	Utility that allows users to exchange messages they type in their terminal windows with other local or remote users.
TELNET	Application layer protocol that allows a user at a client host to log in to a server host. The user's terminal at the client host appears to the server as a directly connected terminal.
Terminal Emulation Services	Transport protocol that provides NetWare workstations access to any OpenVMS systems.
Terminal Server Print Services	Provides an efficient way for OpenVMS users to send print requests to printers attached to TCP/IP-based terminal servers. Users on the host can easily gain access to printers attached to a terminal server as if they were any other OpenVMS printer.
ticket	Kerberos authentication entity that allows a user to prove his identity to an application server by way of a third-party (Kerberos) server.
Time Synchronization Protocol (TSP), or TIMED	Protocol that synchronizes the clocks of the various hosts in a LAN. Also know as timed.
TN3270	Mode used in TELNET to communicate with IBM 3278-n terminal models.
token authentication	An authentication system that allows you to set additional security restrictions on your FTP, TELNET, RLOGIN, and SET HOST logins. Authentication takes place through a physical SecurID token "smart card" that you use to provide the token authentication server (ACE/Server) with the necessary login information. You can set up token authentication through TCPware's Access Control Encryption Client (ACE/Client) on the OpenVMS host, which communicates with Security Dynamics' ACE/Server on a UNIX or Windows NT host.
tokencode	Random number currently displayed on your Security Dynamics SecurID smart card. Used with the token authentication system.
transaction service	Method of data transport provided by UDP that treats each datagram as a separate entity.
Transmission Control Protocol (TCP)	Host layer protocol that provides a reliable data transport service to the application layer protocols. TCP is stream-oriented. It ensures that the system delivers data in order and without duplication.
transparency	Level at which a user need not be aware of the process involved but only in the results of an operation.
trap	Unsolicited message the SNMP agent sends to a management station to inform it that a change in the network occurred. See also Simple Network Management Protocol (SNMP).
UNIX or ULTRIX filesystem	Set of files organized as a tree with a single root node (root) indicated as a slash (/).
User Datagram Protocol (UDP)	Host layer protocol that provides transaction oriented data transport. UDP does not provide data reliability, but does provide data transport with very little overhead.
user ID (UID)	User identification on the UNIX Network File System (NFS) host.
User Identification Code (UIC)	User identification on the OpenVMS host in the format username or [group,member].
VAX byte order	VAX standard for storage and transmission of integers that specifies that the least significant byte appears first. VAX byte order is little-endian. VAX byte order sending machines must translate from the local integer representation to network byte order, and receiving machines must translate from network byte order to the local machine representation.
virtual circuit	Facility in a packet-switched communication network in which packets passing between a pair of terminals stay in sequence. Since this is a property of a circuit, a virtual circuit connects the two terminals. It can be a permanent virtual circuit or a virtual call.
virtual directory	Temporary directory created by the NFS client that is closer to the root in the file structure than the mount point. The virtual directory disappears once you dismount a filesystem.
virtual network	Network in which all connected hosts are able to communicate to each other as if they were all on the same local network. Users view an internet as a virtual network.
Virtual Terminal Protocol	See TELNET.
VMSINSTAL	OpenVMS installation procedure used to install TCPware products.
well-known port	Any of a set of protocol port numbers pre-assigned for specific uses by transport level protocols (TCP and UDP). Servers follow the well-know port assignments so clients can locate them. Examples of well-known port numbers include ports assigned to the remote login (TELNET) service and the file transfer (FTP) servers.
whitespace	Space, tab, or newline character.
WHOIS	Utility that allows Internet users to query the Network Information Center (NIC) username directory services.
wide area network (WAN)	Network element of an internet in which hosts connect over large geographic distances.
X.25	Set of networking recommendations that define the network/user interface in a Packet Switching Data Network (PSDN). X.25 provides a common set of protocols for computer systems to follow when interconnecting over a PSDN.
XQP	Extended QIO processor. See ancillary control process (ACP).