Glossary
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## Glossary

access control list (ACL)

  A list of group codes that a LAT service node includes in a service announcement to designate the LAT users permitted to use the service.

balanced mode

  The state entered by a LAT virtual circuit when it has no data to send. In balanced mode, empty data messages are exchanged between the LAT terminal server and service node to maintain an open virtual circuit.

bandwidth

  The amount of data that can be transmitted in a specific period of time over a physical medium.

circuit timer

  A software timer in a LAT terminal server that determines the interval at which data from user sessions is sent from the terminal server to a service node.

credit

  A marker that a LAT terminal server includes in the slot data of a LAT session to permit the receiving node to transmit a slot of data in reply. The maximum size of slot data accompanying a credit is 255 bytes.

Data Link layer

  In the ISO reference model, the network layer above the Physical Link layer that ensures the safe transport of datagrams between communication endpoints.

datagrams

  Discrete data units, or packets, transferred over networks that have a distinct format dictated by the transport medium.

dual purpose node

  A LAT node that performs both service node and terminal server functions.

dynamic service rating

  A measure of the availability of a LAT service that is calculated by a service node at the time the service is requested.

general purpose node

  A LAT node that performs service node functions.

group code

  A number assigned to a group of LAT users (by means of their terminal ports) and LAT resources to designate access permissions; access is granted when a user's group code matches the group code of the node or service he or she is requesting.

host-initiated request

  A request for service that a LAT service node makes to a terminal server.

identifier list (IDL)

  A list of group codes that a LAT terminal server includes in a connection request to designate the services that the requester is permitted to access.

keep-alive message

  In a LAT network, an empty virtual circuit message that a terminal server and service node exchange to keep an idle connection open.

LAN interface

  An IRIX module that acts as the intermediary between a LAN hardware device (such as an Ethernet board) and the IRIX operating system.

LAT database

  On a terminal server, the body of information that defines the LAT configuration and describes the LAT nodes and services that users can request.

LAT (Local Area Transport)

  A protocol for local area networks that specializes in communications between the hosts and user terminals connected to the network.

LAT node

  In a LAT network, any node running LAT protocol software.

LAT software

  The software that implements the LAT protocol. 4DLT is LAT software that runs on an IRIS host.

latd

  The daemon process on an IRIS node that implements the LAT protocol creates the remote terminal processes upon request by the terminal server.

lati

  An interactive utility used to set the operating parameters for 4DLT software.

load balancing

  Directing new connections to the node with the most available resources. In a LAT network, load balancing is performed by the terminal server, which routes connection requests to the service with the highest rating.

multicast timer

  The software timer in a LAT service node that regulates the interval at which service announcements are dispatched.

multicasting

  The process by which a message is sent to a set of logically related nodes by means of a single, designated address. In a LAT network, the group of related nodes are terminal servers, which receive service announcements by means of a multicast address.

multiplexing

  The ability to combine accumulated user data from simultaneous sessions into a single packet or datagram. Multiplexing is performed by the terminal server and host LAT software.

OSI (Open Systems Interconnection)

  A concept in communications technology, espoused by the International Organization for Standards (ISO), in which networks are designed to permit data exchange among all types of communications equipment. Also, the ISO standard for achieving this interconnectivity, by which networks are designed according to a hierarchy of layers, each of which performs a specified function.

permanent database (LAT)

  Information about the LAT configuration, stored in a file on a LAT terminal server or service node, that is used as the initial database when the LAT protocol is started. (See volatile database.)

Physical Link layer

  In a DECnet network, the lowest layer of network architecture. The Physical Link layer provides the hardware medium and defines the electrical and mechanical interfaces to the medium.

protocol stack

  In networking, the combination of specialized functional layers that constitute a particular protocol, such as OSI or LAT.

service

  A named resource that LAT hosts provide to network users.

service announcement

  A multicast message from a LAT service node that announces the services offered by the node.

Service Class layer

  The uppermost layer in the LAT network protocol. The Service Class layer multicasts service announcements to LAT nodes, maintains directories of LAT nodes and services, and makes services available to LAT users.

service directory

  A collection of LAT service information that is maintained in main memory of a terminal server. For each service, the service directory contains the service name and description, the name of the provider node, the rating and availability of the service, and any group codes associated with it.

service name

  A name, from 1 to 16 characters long, that a LAT administrator assigns to a LAT resource.

service node

  A host or server on a LAT network that offers one or more services to LAT users on terminal servers. An IRIS system running 4DLT software functions as a service node.

service node directory

  A collection of LAT service node information that is maintained in main memory of a terminal server. For each service node, the service node directory contains the name and description of the service node, the network address of the service node, and the node's availability for accepting connections.

service rating

  A measure of the availability of a LAT service that can be dynamically calculated by a service node or assigned a static value by the LAT administrator. LAT service nodes advertise service ratings in service announcements.

session

  An asynchronous, two-way logical connection between a LAT service node and terminal server that enables a user or an application to exchange data with a host providing a LAT service.

  The 4DLT utility used to maintain LAT functions on an IRIS host.

slot

  A segment within a virtual circuit message that contains user data and control information for an individual LAT session.

Slot layer

  In the LAT network protocol, the layer between the Service Class and Virtual Circuit layers. The Slot layer opens and closes sessions, multiplexes slot data into a virtual circuit message, and manages the flow of data between the partner nodes in a LAT session.

static service rating

  A measure of the availability of a service that is assigned by a LAT administrator and remains constant in all service announcements.

terminal server

  A special-purpose communications device that provides LAT connections between its ports and other LAT nodes. Also, a host running software that performs terminal server functions, such as an IRIS system running 4DLT software.

user-initiated request

  A request for a LAT service that a user issues by means of a `CONNECT` command.

virtual circuit

  A logical communication path between a terminal server and a host. The LAT transport mechanism is a virtual circuit.

Virtual Circuit layer

  In the LAT network protocol, the layer between the Slot layer and the Data Link layer. The Virtual Circuit layer establishes and maintains a logical connection (virtual circuit) between LAT partner nodes.

volatile database (LAT)

  The version of the LAT database that is operating in main memory on a LAT terminal server. The volatile database contains the permanent database, information collected from the LAT network, and LAT administrator entries. (See permanent database.)

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