06-6798 Distributed Systems
Glossary of Terms and Acronyms
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Comments and suggestions for additions and amendments are welcome!
Index
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
- asynchronous communication
- A type of communication in which the send operation is non-blocking and receive can be blocing (more common) or non-blocking.
- asynchronous interaction model
- A model of distributed systems in which process execution speeds, message transmission delays and clock drift rates are arbitrary.
- ATM (Asynchronous Transfer Mode)
- A connection-oriented technology defined by the ITU and the ATM Forum. At the lowest level,
ATM sends all data in fixed cells with 48 octets of data per cell.
- authentication
- A method usually based on encryption and shared secrets for establishing the identity of a message sender.
- TERM
- DEFN
B
- bandwith
- The total amount of information that can be transmitted over a network in a given time.
- bridge
- A hardware device that connects two LAN segments and copies frames from one to the other.
Most bridge hardware uses physical addresses to learn which computers attach to which segments so
the bridge can avoid copying frames unless needed.
- broadcast
- A form of delivery not requiring switching in which one copy of a packet is delivered to
each computer on a network.
- TERM
- DEFN
C
- CDR (CORBA Common Data Representation)
- External data representation defined in CORBA 2.0 used to allow programs written in different
languages and running on different platforms to exchange data.
- CGI (Common Gateway Interface)
- A technology used to create dynamic World Wide Web documents. CGI programs run on the
server computer.
- CIDR (Classless InterDomain Routing)
- An address allocation method and routing scheme designed for the IP protocol to make more
effective use of IP addresses.
- circuit switching
- The type of connection used in conventional telephone networks, often referred to as Plain Old
Telephone System.
- client-server architecture
- A widely used architecture model in which client processes interact with individual server
processes on separate host computers in order to access shared data.
- collision
- An event that occurs on a CSMA/CD network when two stations attempt to transmit
simultaneously. The signals interfere with each other, forcing the two stations to back off and try again.
- connectionless communication service
- A communication service, e.g. UDP, based on the sending and receiving of
messages which can get lost/duplicated/delivered out of order/corrupted without telling the user.
- connection-oriented communication service
- A communication service, e.g. TCP, based on establishing a data stream connection to ensure
reliable in-sequence delivery of data.
- CORBA (Common Object Request Broker Architecture)
- A design for middleware that allows programs written in different programming languages and running on different platforms and
network architectures to communicate with each other.
- CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
- A CSMA network that has the capability to avoid errors that result when multiple stations
transmit simultaneously by exchanging request-to-send and clear-to-send messages to reserve a
slot for transmission.
- CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
- A CSMA network that has the capability to detect errors that result when multiple stations
transmit simultaneously. See collision.
- TERM
- DEFN
D
- datagram
- The form of a packet sent across a network. Each datagram has a header that identifies
both the sender and receiver followed by data.
- dependability
- The set of requirements placed on a computer system which ensures its correctness, security
and fault-tolerance.
- distributed system
- A system of networked computers which communicate and coordinate their actions only by passing
messages.
- domain
- A part of the computer naming hierarchy used in the Internet. For example, commercial
organizations have names registered under the .com domain.
- DNS (Domain Name System)
- A name service on the Internet which provides a database of domain names which
can be queried to resolve names (translate domain names to IP addresses).
- TERM
- DEFN
E
- Ethernet
- A popular Local Area Network technology that uses a shared bus topology and CSMA/CD
access. Basic Ethernet operates at 10 Mbps, Fast Ethernet operates at 100 Mbps, and Gigabit Ethernet
operates at 1000 Mbps (i.e., 1 Gbps).
- TERM
- A part of the computer naming hierarchy used in the Internet. For example, commercial
organizations have names registered under the .com domain.
F
- fault-tolerance
- The ability of a computer system to function correctly in the presence of faults in hardware,
software and networks.
- firewall
- A collection of processes whose role is to monitor and control all information into and out of an intranet.
- FTP (File Transfer Protocol)
- A protocol used to transfer a complete file from one computer to another.
- frame relay
- A network technology that provides connection-oriented service, bringing some of the advantages
of circuit switching to packet-switching networks, for example ATM.
- TERM
- DEFN
G
- group communication
- A method of communication based on multicasting messages to a group of processes. The sender is unaware of the
size and membership of the group.
- TERM
- DEFN
H
- host
- An end-user's computer connected to a network. In an internet, each computer is classified as
a host or a router.
- HTML (HyperText Markup Language)
- The source form used for documents on the World Wide Web. HTML embeds commands that
determine formatting along with the text to be displayed (e.g., to move to a new line or indent text).
- HTTP (HyperText Transport Protocol)
- The protocol used to transport a World Wide Web page from one computer to another.
- hub
- An electronic device used to extend a network by providing sockets to which computers can be
connected as if they were attach to a network.
- TERM
- DEFN
I
- intranet
- A portion of a network that is separately administered and has a boundary that can be configured
to enforce local security policies.
- Internet
- The global network of interconnected computers which communicate through IP protocols.
- IP (Internet Protocol)
- The protocol that defines both the format of packets used on a TCP/IP Internet and the
mechanism for routing a packet to its destination.
- IPv4 (Internet Protocol Version 4)
- The version of IP currently used in the Internet. IPv4 uses 32-bit addresses.
- IPv6 (Internet Protocol Version 6)
- A specific protocol that has been chosen by the IETF as a successor to IPv4. IPv6 uses 128-bit
addresses.
- ISP (Internet Service Provider)
- A commercial organization that provides its subscribers with access to the Internet.
- IP address resolution protocol
- The part of the IP protocol which is responsible for converting Internet addresses to network addresses for the
underlying network, e.g. in the case of Ethernet this involves translating 32-bit Internet addresses to 48-bit
Ethernet addresses.
- IP datagram
- The form of a packet sent across a TCP/IP internet. Each datagram has a header that identifies
both the sender and receiver followed by data.
- IP Multicast
- The protocol built on top of IP which implements group communication. The membership of a multicast group
is dynamic.
- IP routing
- The layer of software in the IP protocol which routes packets from source to destination.
- TERM
- DEFN
J
- jitter
- The variation in the time taken to deliver series of messages, which is relevant to multimedia
data.
- TERM
- DEFN
K
- TERM
- DEFN
L
- LAN (Local Area Network)
- A network that uses technology designed to span a small geographic area. For example, an
Ethernet is a LAN technology suitable for use in a single building. LANs have lower propagation delay
than WANs. See WAN.
- latency
- The time taken by the first of a string of bits to reach its destination, typically
measured by the time needed to transmit an empty message.
- TERM
- DEFN
M
- MAN (Metropolitan Area Networks)
- The type of network installed in cities over copper and fibre optic cabling for the
transmission of multimedia data over distances up to 50km.
- marshalling of data
- The process of translating a collection of data items into a form suitable for transmission, such as binary or ASCII. See CORBA CDR.
- middleware
- The lowest layer of hardware and software layers, typically hardware plus operating system.
- MIME (Multipurpose Internet Mail Extensions)
- The standard for sending multipart data, containing e.g. sound, text and video, by email.
- mobile agents
- A running program (code + data) that travels from one computer to another in a network
carrying a task, such as collecting information, eventually returning with results.
- mobile code
- The code that is downloaded from the server to the client machine and run locally, e.g.
Java applets.
- MobileIP
- A protocol which enables mobility of portable computers.
Each laptop retains its IP number, but communications are routed through
a Home Agent (if at home). Home Agent is notified before going away, and
communication is re-routed through Foreign Agent based at the destination.
- MTU (Maximum Transmission Unit)
- The largest amount of data that can be sent across a given network in a single packet. Each
network technology defines an MTU (e.g., the MTU of an Ethernet is 1500 octets).
- multicasting
- Simultaneous transmission of messages to several recipients.
- TERM
- DEFN
N
- TERM
- DEFN
O
- One-copy update semantics
- Type of service offerred by conventional file systems where concurrent
updates of the contents of a file by several processes is as if there was only
one copy of the
file in the system. If caching or replication is used then there is
a delay until updates propagate into a file, with the effect being a
semantics different from one-copy semantics.
- TERM
- DEFN
P
- packet switching
- A widely used type of communication network that accepts and delivers individual packets of
information. Also called store-and-forward network.
- performance
- The set of measurements that can be applied to distributed systems to express its responsiveness
to client requests, throughput and ability to meet timeliness guarantees (e.g. probability
of meeting a time deadline).
- platform
- The lowest layer of hardware and software layers, typically hardware plus operating system.
- principal
- The authority, ususally possessing a collection of access rights, on whose behalf a method
invocation or result is issued.
- proxy server
- A server which provides a shared cache of resources for the client machines at a site or
across several sites. The purpose of web proxy servers is to reduce load on the wide-area
network and to act as a security measure across firewall.
- protocol suite
- A set of protocols that work together to provide a seamless communication system. Each protocol
handles a subset of all possible details. The Internet uses the TCP/IP protocol suite. See stack.
- public key protocol
- A cryptographic protocol based on the use of public keys, i.e. paramemeters without which the
message cannot be decrypted.
- TERM
- DEFN
Q
- Quality of Service
- The non-functional properties of a service experienced by clients and users which typically
include properties such as reliability, security and performance. (More recenly also
adaptability).
- TERM
- DEFN
R
- reliability
- A protocol is said to be reliable if it delivers messages without loss or corruption across
a transmission medium.
- replication
- A method of increasing the reliability of systems based on multiple copies of data or devices.
- router
- The basic building block of an internet. A router is a computer that attaches to two or more
networks and forwards packets according to information found in its routing table. Routers in the Internet
run the IP protocol. See host.
- RIP (Router Information Protocol)
- The protocol run in a router which determines the next hop of a packet and periodically updates
its routing table based on the information received from its neighbours.
- RMI (Remote Method Invocation)
- Method invocations between objects in different processes. See Java RMI.
- RPC (Remote Procedure Call)
- Procedure calls between different processes. See Sun RPC.
- TERM
- DEFN
S
- security
- The set of measures employed by a distributed system to ensure the protection of shared data
and objects against enemy attacks.
- SMTP (Simple Mail Transfer Protocol)
- A protocol for email communications.
- socket abstraction
- An endpoint for communication between processes supported by most operating systems, which
is bound to a local port and an Internet address.
- synchronous communication
- A type of communication in which both send and receive are blocking operations.
- synchronous interaction model
- A model of distributed systems in which lower/upper time bounds are known for
the time to: execute each step, transmit a message and clock drift rates.
- TERM
- DEFN
T
- TCP (Transmission Control Protocol)
- The TCP/IP protocol that provides application programs with access to a connection-oriented
communication service. TCP offers reliable, flow-controlled delivery. More important TCP
accommodates changing conditions in the Internet by adapting its retransmission scheme. See UDP.
- TCP/IP
- The protocol suite used in the Internet. Although the suite contains many protocols, TCP and IP
are two of the most important.
- thin client
- A software layer that supports a window-based user interface on a computer that is local to
the user while executing application programs on a remote computer.
- tunnelling
- A type of communication needed when a pair of nodes belonging to different networks
communicate through an 'alien' protocol.
- TERM
- DEFN
U
- UDP (User Datagram Protocol)
- A transport-level protocol for transmitting messages between processes which does not guarantee delivery.
- URL (Uniform Resource Locator)
- A syntactic form used to identify a page of information on the World Wide Web.
- TERM
- DEFN
V
- TERM
- DEFN
W
- WAN (Wide Area Network)
- A network that uses technology designed to span a large geographic area. For example, a satellite
network is a WAN because a satellite can relay communication across an entire continent. WANs have
higher propagation delay than LANs. See LAN.
- WAP (Wireless Application Protocol)
- A protocol developed for use on wireless portable devices to access services such as WWW.
- WLAN (Wireless Local Area Network)
- A network that uses wireless communication technology such as IEEE 802.11 WaveLAN designed to
be used in place of LANs.
- WPAN (Wireless Personal Area Network)
- A network that uses infra-red links or the BlueTooth low-power radio technology used for
conencting computers to local printers, palmtops, etc.
- WWW (The World Wide Web)
- The evolving system for publishing and accessing resources and services across the Internet based
on the following technologies: HTTP, URLs and client-server architecture.
- TERM
- DEFN
X
- XML (Extensible Markup Language)
- Metalanguage for describing data, successor to HTML.
- TERM
- DEFN
Y
- TERM
- DEFN
Z
- TERM
- DEFN
Dr Marta Kwiatkowska
University of Birmingham, School of Computer Science