Glossary

active user: In an XTI transport connection, the transport user that initiated the connection. See also client process and passive user.

Address Resolution Protocol (ARP): The Internet (TCP/IP) Protocol that can dynamically resolve an Internet address to a physical hardware address. ARP can be used only across a single physical network and in networks that support the hardware broadcast feature.

asynchronous event: See event.

asynchronous execution

Execution of processes or threads in which each process or thread does not await the completion of the others before starting.
In XTI, a mode of execution that notifies the transport user of an event without forcing it to wait.

Berkeley Software Distribution: UNIX software release of the Computer Systems Research Group (CSRG) of the University of California at Berkeley.

blocking mode: See synchronous execution.

BSD socket interface: A transport-layer interface provided for applications to perform interprocess communication between two unrelated processes on a single system or on multiply connected systems. This interprocess communications facility allows programs to use sockets for communications between other programs, protocols, and devices.

client process: In the client/server model of communication, a process that requests services from a server process. See also active user.

communication domain: An abstraction used by the interprocess communication facility of a system to define the properties of a network. Properties include a set of communication protocols, rules for manipulating and interpreting names, and the ability to transmit access rights.

connection-oriented mode: A mode of service supported by a transport endpoint for transmitting data over an established connection.

connectionless mode: A mode of service supported by a transport endpoint that requires no established connection for transmitting data. Data is delivered in self- contained units, called datagrams.

datagram: A unit of data that is transmitted across a network by the connectionless service of a transport provider. In addition to user data, a datagram includes the information needed for its delivery. It is self-contained, in that it has no relationship to any datagrams previously or successively transmitted.

datagram socket: Socket that provides datagrams consisting of individual messages for transmission in connectionless mode.

error: In XTI, an indicator that is returned by a function when it encounters a system or library error in the process of executing. The object is to allow applications to take an action based on the returned error code.

eSNMP: The Extensible Simple Network Protocol (eSNMP) enables you to create subagents to be mananged by an SNMP management station. See Chapter 6.

Ethernet: A 10-megabit baseband local area network (LAN) using carrier sense multiple access with collision detection (CSMA/CD). The network allows multiple stations to access the medium at will without prior coordination, and avoids contention by using carrier sense and deference, and detection and transmission.

ETSDU: See Expedited Transport Service Data Unit and out-of-band data.

event: An occurrence, or happening, that is significant to a transport user. Events are asynchronous, in that they do not happen as a result of an action taken by the user.

event management: A mechanism by which transport providers notify transport users of the occurrence of significant events.

expedited data: Data that is considered urgent. The semantics of this data are defined by the transport provider. See also out-of-band data.

Expedited Transport Service Data Unit: In XTI, an expedited message in which the identity of the data unit is preserved from one end of a transport connection to the other.

file descriptor: A small unsigned integer that a UNIX system uses to identify a file. A file descriptor is created by a process through issuing an open system call for the file name. A file descriptor ceases to exist when it is no longer held by any process.

host group: A group of zero or more hosts that, for the purposes of IP multicasting, are identified by a single class D IP destination address. Class D IP addresses have 1110 as their high-order four bits. See IP Multicasting for more information.

ICMP: See Internet Control Message Protocol.

\#include file.h: A C language precompiler directive specifying interpolation of a named file into the file being compiled. The interpolated file is a standard header file (indicated by placing its name in angle brackets) or any other file containing C language code (indicated by placing its name in double quotation marks).
The absolute path name of header files whose names are placed in angle brackets (60; \>) is /usr/include/file.h.

International Standards Organization (ISO): An international body composed of the national standards organizations of 89 countries. ISO issues standards on a vast number of goods and services, including networking software.

Internet Control Message Protocol (ICMP): A host-to-host protocol from the Internet Protocol (IP) suite that provides error and informational messages on the operations of the IP.

Internet Protocol (IP): The Internet Protocol that provides a connectionless service for the delivery of datagrams across a network.

ISO: See International Standards Organization.

IP Multicasting: IP Multicasting is a method for transmitting IP datagrams to a group of hosts identified by a single IP destination address, or host group. Host groups are identified by class D IP addresses. See host group for more information.

Management Information Base: See MIB.

MIB: The Management Information Base (MIB) definitions are a set of data elements that relate to network management. See Chapter 6.

name server: A daemon running on a system that client processes contact to obtain the addresses of hosts or other objects in a network. This daemon translates a machine's network name to its network IP address.

name service: The service provided to client processes for identifying peer systems for communications purposes.

nonblocking mode: See asynchronous execution.

normal data: Regular data that is sent or received in band by a transport user. See also out-of-band data.

Object Identifier: See OID.

OID: Object Identifiers (OID) are data elements in MIB definitions that can be referred to by name or by a corresponding sequence of numbers. See Chapter 6.

Open Systems Interconnection (OSI): The interconnection of open systems in accordance with ISO standards.

orderly release: In XTI, an optional feature that allows a transport user to gracefully terminate a transport connection with no loss of data.

OSI: See Open Systems Interconnection.

out-of-band data: Data that is transmitted out of the flow of normal data because it is considered urgent. The receiving process is notified of the presence of this data so that it can be retrieved.

passive user: In an XTI transport connection, the peer transport user that responded to the connection request. See also active user and client process.

pipe: An I/O stream that has a descriptor and can be used in unidirectional communications between related processes. See also socketpair.

raw socket: A socket that provides privileged users access to internal network protocols and interfaces. These socket types can be used to take advantage of protocol features not available through more normal interfaces or to communicate with hardware interfaces.

Serial Line Internet Protocol (SLIP): A transmission line protocol that encapsulates and transfers IP datagrams over asynchronous serial lines.

server process: In the client/server model of communication, a process that provides services to client processes. See also passive user.

SLIP: See Serial Line Internet Protocol.

socket: In interprocess communications, an endpoint of communication. Also, the system call that creates a socket and the associated data structure.

socketpair: A pair of sockets that can be created in the UNIX domain for 2-way communication. Like pipes, socketpairs require communicating processes to be related. See also pipe.

state: In XTI, the current condition of a process that reflects the function in progress. XTI uses eight different states to manage communications over a transport endpoint.

stream socket: A socket that provides 2-way byte streams across a transport connection. Also includes a mechanism for handling out-of-band data.

STREAMS: A kernel mechanism specified by AT&T that supports the implementation of device drivers and networking protocol stacks. See also STREAMS framework.

STREAMS framework: Components of the AT&T STREAMS mechanism which define the interface standards for character I/O within the kernel and between the kernel and user levels. It consists of functions, utility routines, kernel facilities, and data structures.

synchronous execution: A mode of execution that forces transport primitives to wait for specific events before returning control to the transport user.

TCP: See Transmission Control Protocol.

TCP/IP: The two fundamental protocols of the Internet Protocol suite, and an acronym that is frequently used to refer to the Internet Protocol suite. TCP provides for the reliable transfer of data, while IP transmits the data through the network in the form of datagrams. See also Transmission Control Protocol and Internet Protocol.

TLI: See Transport Layer Interface.

Transmission Control Protocol (TCP): The Internet transport-layer protocol that provides a reliable, full-duplex, connection-oriented service for applications. TCP uses the IP protocol to transmit information through the network.

transport endpoint: A communication path over which a transport user can exchange data with a transport provider. See also Transport Layer Interface.

Transport Layer Interface (TLI): An interface to the transport layer of the OSI model, designed on the ISO Transport service definition.

transport provider: A transport protocol that offers transport layer services in a system.

Transport Service Data Unit (TSDU): In OSI terminology, the item of information, or message, that the transport user passes to the transport provider.

transport services: The support given by the transport layer in a system to the application layer for the transfer of data between user processes. The two types of services provided are connection-oriented and connectionless. See also Transport Layer Interface.

transport user: A program needing the services of a transport protocol to send data to or receive data from another program or point in a network. See also Transport Layer Interface.

TSDU: See Transport Service Data Unit.

UDP: See User Datagram Protocol.

User Datagram Protocol (UDP): The Internet Protocol that allows application programs on remote machines to send datagrams to one another. UDP uses IP to deliver the datagrams.

X/Open Transport Interface: Protocol-independent, transport-layer interface for applications. XTI consists of a series of C language functions based on TLI, which in turn was based on the transport service definition for the OSI model.

XTI: See X/Open Transport Interface.