ACSE
Association Control Service Element (ISO/IEC 8649, 8650): set of functions for setting up, maintaining, and clearing down Layer 7 connections between applications.
API
Application Programming Interface: an interface that is freely available to application programmers and provides a set of interface mechanisms based on a specific range of functions.
application gateway
Gateway that acts as a switch between two applications with interdependent services and that maintains two independent relationships with the partners.
ASN.1
Method for specifying the structure of protocol elements defined by CCITT and ISO (ISO 8824 and 8825).
automatic tunnel
A tunnel that is automatically generated through the use of IPv4-compatible IPv6 addresses.
backbone
A network used for linking several other connected networks, known as front-end networks, to which systems, their applications, and users are attached.
bridge
Device or system that directly links two LANs, working only with data (mainly addresses) of the Data Link Layer. A “normal” bridge, also called a local bridge, links two LANs directly; a remote bridge links two LANs that have the same technology via a WAN.
broadcast, multicast
Transmission of a message to several or all receivers in a network who are addressed by means of a broadcast address or group address. Reception is not generally guaranteed.
CCITT
Comité Consultatif International Télégraphique et Téléphonique (International Telegraph and Telephone Consultative Committee), a subagency of the UN that issues definitions in the field of telecommunications services (renamed ITU-TSS in 1993).
CEN
Comité Européen de Normalisation: European standardization body that develops nonelectrical standards for Europe. The German member is the DIN.
CENELEC
Comité Européen de Normalisation Electrotechnique: European standardization body that develops electrical standards for Europe. The German member is the DKE.
circuit switching
See CSDN.
client
Term from the client/server architecture: the partner that calls on the services of the server.
client
Logical instance which sends requests to a server.
CMIP
Common Management Information Protocol: protocol standardized by ISO for the transfer of network management operations and event reports between open systems.
CMIS
Common Management Information Services: services standardized by ISO for accessing objects and information relevant for network management.
communication architecture
Model of the communication world.
communications server
A system that supports client communication in a client/server architecture so that clients do not have to perform complex communication tasks such as the handling of protocols. A communications server functions primarily as a gateway.
connection
Communication relationship, the characteristics and quality of which are monitored by a service provider.
connectionless
Characteristic of a communication relationship in which there is no relation between the messages and no monitoring by the service provider. Relationships between the pieces resulting from segmentation are often taken into account.
connection-oriented
Characteristic of a communication relationship; see connection.
connectivity
Generally speaking, the possibility of communication between systems and partners; sometimes also used to refer only to the communication options involving transport systems.
convergence protocol
See harmonization protocol.
CSDN
Circuit-Switched Data Network: public or private network that switches circuits between two partners for the purpose of exchanging messages. Sometimes called an X.21 network.
CSMA/CD
Carrier Sense Multiple Access / Collision Detection. A protocol defined in IEEE 802.3 and ISO 8802-3 for LANs. Ethernet and 802.3 are similar, but both use the CSMA/CD protocol. For this reason, the two terms are often used synonymously.
data compression
Reduction of data by compression.
datagram
Term for messages that are sent in connectionless communication. There is no guarantee that datagrams will reach the receiver at all, that they will arrive in the correct order, or that they will not arrive more than once.
DCE
Data Communication Equipment: in public networks, the public network device to which the data termination equipment (DTE) is connected. The public network operator’s domain ends here.
DCE
Distributed Computing Environment: a product package from the Open Software Foundation (OSF) for distributed processing with a number of facilities.
dedicated circuit
Dedicated connection between two communication partners that is available at all times without requiring a setup phase.
de-facto standard
Standard not created by an acknowledged standardization body but generally accepted. May be transformed into an internationally agreed standard.
de-jure standard
International standard issued by ISO or CCITT, or a national standard issued by a national standardization body.
DIN
Deutsches Institut für Normung (German standardization institution): official standardization body in Germany for non-electrical standards; member of CEN and ISO; also responsible for IT standards.
directory
Container for information used to identify suitable routes from user and system IDs with the aid of directory services. The standard is defined in CCITT X.500 and ISO 9594.1-8.
directory services
Products based on the standard directory. Depending on requirements, directory services can be used to manage different types of information (e.g. for comparing the interests of telephone centers and airline companies), but due to their compliance with standards can interoperate world-wide.
distributed processing
Synergetic use of the resources located on various systems in a network
DME
Distributed Management Environment: product package from OSF for distributed system and network management.
DNS
(Domain Name System)
System for administering names and addresses on the Internet.
domain
Area of a network in which similar or coordinated functions and methods that are controlled by an entity are valid for a specific range of functions. Examples: management domain, routing domain with uniform routing function, security domain with uniform security policy (see Brochure 7 “Security”), addressing domain with an entity responsible for address assignment.
DQDB
Distributed Queue Dual Bus: a function defined in IEEE 802.5 and ISO 8802-5 for a metropolitan area network that is easily migrated to ATM networks. A connectionless variant is SMDS.
Draft
Preliminary stage of an RFC.
DTE
Data Termination Equipment: in public networks, a terminal that is connected to the network via a DCE and is under the charge of the user.
dynamic right-sizing, inbound
Based on the measurement of the minimum round trip time, inbound dynamic right-sizing estimates the sender’s congestion window. The congestion window is calculated with the maximum received data volume during the minimum round trip time. This measurement is used to calculate the necessary receive window and the corresponding size of the receive buffer that is to be made available.
dynamic right-sizing, outbound
Based on the measurement of the minimum round trip time, outbound dynamic right-sizing estimates the continuously available network capacity and therefore also the required congestion window. The network capacity is calculated with the maximum data volume acknowledged by the receiver during the minimum round trip time. This measurement is used to calculate the necessary congestion window and the corresponding size of the send buffer that is to be made available.
ECN
The Explicit Congestion Notification (RFC 3168) Mechanism is used to prevent the loss of packets in heavy-load situations. ECN is realized through the interaction of TCP and IP.
emulation
Component that emulates the characteristics of another device.
encapsulation
Method for transferring messages via a network. The entire message, i.e. header and data, is transported (encapsulated) as a user message in the intermediate network.
end system
Term in the OSI architecture: system which, unlike an intermediate system, has a resident transport entity (and thus applications) that uses the network functions via NSAPs. Physically, the end system itself can comprise several hardware components. Also used in other architectures in a similar manner.
entity
Term in the OSI architecture: active element on a layer.
Extension header
IPv6 headers which contain optional information which does not form part of the IPv6 basic header.
Ethernet
A LAN introduced by XEROX that is based on yellow cable and uses CSMA/CD as a transmission method. Similar to an IEEE 802.3 LAN.
evaluation
Evaluation of a system in accordance with security criteria.
gateway
Term generally used to designate a system that links two or more networks and does not operate as a bridge. Variants: gateway on the Network Layer (= router or OSI relay), transport gateway, and application gateway.
harmonization protocol (a.k.a. convergence protocol)
Protocol that serves to adapt one service provided by a protocol stack to another service, i.e. it harmonizes one service with the other.
HDLC
High-level Data Link Control: protocol defined in several ISO standards, such as ISO 7776, and used on the Data Link Layer to link two systems or devices.
heterogeneous network
A network that is made up of several different subnetworks based on different technical principles
heterogeneous X.25 coupling
Direct utilization of the network service for X.25 networks without a transport protocol (e.g. for X.28 and X.29).
high-speed TCP
TCP with the additional mechanisms “large congestion windows” and ”limited slow start” in order to reduce downtimes when errors occur: Network topologies in which the product of bandwidth and network runtime represents a large value can only be optimally used with TCP if large windows are available. However, inherent to the use of large windows is the problem that, under certain circumstances, many TCP segments may be lost when errors occur and it can take a long time to reach the original window size again after the error.
homogeneous network
A network set up according to a single technical principle.
host
Formerly a large data processing system that required a front-end processor for communication. Now designates BS2000 systems or MVS systems in SNA, and others.
hub
Line concentrator/star coupler from which lines are connected to a large number of stations in a star formation, even if the stations are logically connected in a ring. Today, hubs can integrate powerful management, bridge, and routing functions.
IAB
Internet Architecture Board: controls new developments in the internet network using the RFC mechanism.
IEC
International Electrotechnical Commission: international standardization body for electrical standards that was founded by ISO and the Joint Technical Committee 1 for IT standards. The German member is the DKE.
IEEE
Institute of Electrical and Electronic Engineers: US association of engineers which has done foundational work mainly in the LAN field, which has defined standards in the past, and which continues to do so.
industry standard
Synonymous with de-facto standard: standard which is generally accepted in a particular industry because of market forces.
integrity
Completeness and accuracy of processed, transferred, and stored data.
intermediate system (IS)
A system that logically contains only the lower three OSI layers and links various networks as a relay. Opposite of an end system. Functionally identical to a router.
Internet
Communication architecture characterized by its use of TCP and IP that resulted from the ARPA network in the USA. Expansions are controlled by the IAB by means of the RFC process.
internetworking
General term for the linking of communication networks of all types; various methods can be used.
IPng
IP next generation, synonym for IPv6
IPSEC
IP security protocol extends IP protocol by security mechanisms. It includes encryption and authentication methods used in isolation and together.
IPv4
Internet Protocol: connectionless network protocol in the Internet architecture which uses 4-byte long addresses.
IPv6
Internet Protocol: connectionless network protocol in the Internet architecture which uses 16-byte long addresses and is the successor to IPv4.
IPv6 basic header
See primary IPv6 header
ISO
International Organization for Standardization
ITU
International Telecommunications Union, a UN subagency.
ITU-TSS
Telecommunications Standards Sector, with the same functions as the former CCITT.
LAN
Local area network: originally a high-speed, short-range network. Today, also any network with a long range that operates as per CSMA/CD or token ring.
large congestion windows
Following successful error recovery, high-speed TCP for large congestion windows determines the size of the congestion window on the basis of the current size of the congestion window. (Standard TCP always halves its congestion window.) This reduces the time taken to reach the size of the original congestion window. This mechanism is defined in RFC 3649.
limited slow start
When this mechanism for high-speed TCP with large congestion windows is used, the slow start runs more slowly than in standard TCP as of a given congestion window size. This limits the number of TCP segments that may be lost if an error occurs during the slow start of a connection. The mechanism is defined in RFC 3742.
Link
Direct connection between two systems (end system/router)
Link Layer
Communication layer that guarantees direct communication between two systems (end system/router) in a network
LLC
Logical link control: protocol defined in IEEE 802.2 and ISO 8802-2 that is used in LANs above the MAC layer in order to control connection-oriented or connectionless communication.
MAC
Medium Access Control: describes the rules and methods for LAN access.
MAC address
Address of a device connected to a LAN, e.g. the internationally unique Ethernet address. These addresses are evaluated by bridges so that the destination system can be found.
MAN
Metropolitan area network: a network that provides LAN-like services and communication options over a range of approx. 50 to 150 km. Examples: DQDB, SMDS.
managed object
(short form: object)
Abstract representation of a network resource with respect to characteristics relevant to network management.
manager
Managing system for network management operations.
message handling
The method described in Recommendation X.400 for sending and exchanging messages.
MSCF
Subsystem of BS2000 that provides the privileged components (MSCF applications) of the operating system services for communication with other BS2000 instances. MSCF uses BCAM for communication.
multicast
See broadcast.
multiplexer
Network component that permits data streams to be multiplexed via a line or connection for optimum utilization of the bank width.
multiprotocol router
Router that can route communication relationships with different protocol stacks.
named pipe
Interface for bidirectional communication between servers and clients that is made available by the LAN Manager.
NEA
Name of a network architecture.
Network Layer
Communication layer that guarantees communication between the different end systems in a network.
network service
Service provided on the Network Layer of the OSI model with two variants: connectionless and connection-oriented (ISO 8348).
OIW
See EWOS.
OSF
Company founded by a group of vendors that provides open products for Unix systems, such as Motif, DCE, DME, and the OSF/1 operating system.
OSI
Open Systems Interconnection: communication architecture defined in ISO 7498; adopted by CCITT as Rec. X.200.
OSPF
Open Shortest Path First
Interior gateway protocol.
peer-to-peer communication
Communication model in which two partners of a relationship are equal and cannot act in a master/slave relationship.
Portability Guide
Document published by X/Open that defines functions to be provided for a number of function complexes and how these functions are to be provided. The latest version is XPG4.
POSIX
Portable Open System Interface: a forum and the standards created by this forum for portable system interfaces on various system platforms.
PPP
Point-to-Point Protocol: defined in RFC 1171. Serves as a protocol between routers and via serial lines for the purpose of transporting and multiplexing different network protocols.
presentation service
Service on the Presentation Layer of the OSI model that is standardized in ISO 8822.
primary IPv6 header
First IPv6 header. Its content includes the address information of the IPv6 packet. It is the only IPv6 header that is always present in an IPv6 packet.
privilege
Set of user attributes used by the access control system.
profile
In OSI, a standard that defines which protocols are to be used for a specific purpose and contains regulations regarding the values of parameters and options.
protocol
The totality of rules and methods used between two or more partners for achieving a defined purpose, usually taking the form of a definition of messages to be exchanged and of the correct execution of message sequences incl. handling of errors and other exceptional situations.
protocol relay
Relay that serves as a switch between two partners, translating the protocol elements from one end to protocol elements at the other end and initiating other protocol-compliant actions.
PSDN
Packet-Switched Data Network: public or private network in which no lines are through-connected between the communication partners; instead, the packets can take various routes through the network, depending on the workload, etc., and are re-sorted at the interface to the partner. Example: networks based on X.25.
relay
In OSI, designates an element on a layer that serves as a switch between two partners. Thus, first of all, it permits communication between these two partners. In a narrower sense, a relay on the Network Layer is the functional equivalent of a router.
repeater
Element on the Physical Layer that extends the range of a medium.
RFC
Request for Comment: method used in internet for commenting on recommended standards, definitions, or reports; also the name of a document issued by means of this process.
router
Element in a network that resides between networks and forwards message streams through the network while handling routing, flow control, addressing, and other functions. Operates on Layer 3 of the OSI model.
routing domain
Domain in a network in which the same routing methods and routing protocols are used. Routing is controlled from a single, responsible point.
routing protocol
Protocol by which routers obtain information on topologies, modifications, and costs of routes from one another or from the connected end systems.
server
Logical entity or application component that performs client operations and provides the (coordinated) usage of generally available services (File, Print, DB, communication, etc.). It can itself be the client of another server.
service
Complete, well-defined set of functions made available by a service provider to a service user; in OSI, primarily a service on a layer.
session
In OSI, designates a Layer 5 connection.
session service
Service on the Session Layer of the OSI model that is standardized in ISO 8326.
SLIP
Serial Line Interface Protocol: defined in RFC 1055.
SMDS
Switched Multimegabit Data Service: high-speed network that provides connectionless traffic based on and compatible with DQDB.
SMTP
Simple Mail Transfer Protocol: simple e-mail program from DARPA services, which is provided as standard in Unix systems.
SNMP
Simple Network Management Protocol: protocol defined in Internet for TCP/IP for the transfer of management information.
standard
Document containing definitions and requirements in order to fulfill a well-specified function or purpose. See also de-facto standard, industry standard, de-jure standard.
streams
A runtime environment in Unix systems with standardized interfaces that permits the dynamic and flexible creation and modification of protocol stacks for communication during operation.
subnetwork
Technically or administratively homogeneous part of a network.
subsystem
Part of a system that processes a self-contained function complex.
switch
Multiport bridge based on a hardware implementation that routes data traffic via multiple ports to multiple network segments.
TCP
Transmission Control Protocol: transport protocol in the internet architecture.
TCP/IP
Another name for the internet architecture.
terminal
End device used for data input/output, e.g. screen with keyboard, printer, swipe card reader.
terminal access method
Program interface in the host that defines simple interfaces and tools in the respective programming language to facilitate dialog with terminal users.
token ring
Technique used in token ring LANs, by which a token circulates in a ring-shaped LAN and regulates the transmission rights of the different stations.
transaction
Sequence of logically related processing steps, all or none of which must be processed.
transport gateway
Gateway or relay that operates on the Transport Layer and concatenates two transport connections.
transport protocol stack
Set of related protocol functions for OSI Layers 1 through 4.
transport system
Part of a system or architecture that provides approximately the same functions as the bottom four OSI layers, i.e. the transport of messages from one partner in a communication relationship to another.
transport system interface
Interface that provides upward access to the functions of the transport system and allows them to be used. The functions of the TSI depend on the transport system below it.
TSS
Telecommunications Standards Sector of ITU, formerly CCITT.
tunnel
Mechanism for the transmission of IPv6 packets compressed as IPv4 packets over an existing IPv4 infrastructure.
tunneling
Technique by which the information in a protocol element of network A is converted to a protocol element of network B and retrieved in network C. Technically and with regard to protocols, C is almost identical to A. However, tunneling is also possible, for example, from SDLC to token ring.
Virtual Local Area Network (VLAN)
Virtual Local Area Network: described in IEEE 802.1q and based on the mode of operation of a LAN, today also a network with a large range. The VLANs are classified by specifying a VLAN ID and a user priority.
VLAN-Identifikation (VLAN Id)
The assignment of a VLAN identification (abbreviated as VLAN Id) is defined in the VLAN. This Id is an integer from the range <2..4094>. VLAN Id 0 classifies an ’untagged’ VLAN.
WAN
Wide area network: public or private network that bridges long distances and, unlike LANs, operates at a relatively low speed with a higher error rate. In ATM networks, for example, these two characterizations no longer apply.
X/Open
Syndicate of various vendors and users that draw up specifications in order to produce portable products that can be implemented in multivendor networks, thereby creating open systems primarily in the Unix system area.