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Network Glossary |
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A variant of Ethernet which allows stations to be attached via twisted pair cable at 10 Mbps. 10BaseFL A variant of Ethernet which allows stations to be attached via fibre optic cable at 10 Mbps. 100BaseT A variant of Ethernet which allows stations to be attached via twisted pair cable at 100 Mbps. 2950 Ethernet Switch A 2950 Cisco Ethernet switch is the standard type switch that the University deploys into the access layer of the QUT Network. 3750 Ethernet Switch A 3750 Cisco Ethernet switch is the standard type of switch that the University deploys into the distribution layer of the QUT Network. 6500 Switch/Router A 6500 Cisco Layer 3 switch is the standard type of router that the University deploys into the core layer of the QUT Network. 802.x The set of IEEE standards for the definition of LAN protocols. Abbreviation for "Automatic Call Distributor". A device that distributes incoming calls to a specific group of terminals (Within QUT - this function is performed by CCD and Genesys). Access Layer The Cisco hierarchical network design model defines the access layer as the point at which local end users are allowed into the network. This layer ensures that network packets are delivered to end user computers. Network devices used at this layer are known as “access devices”. At QUT the access layer consists of layer2 switches that support connections from end user computers and wireless access points. Address There are three types of addresses in common use within the Internet. They are email address; IP, internet or Internet address; and hardware or MAC address. Address Mask A bit mask used to identify which bits in an IP address correspond to the network and subnet portions of the address. This mask is often referred to as the subnet mask because the network portion of the address can be determined by the encoding inherent in an IP address. Address Resolution Conversion of an internet address into the corresponding physical address. Address Resolution Protocol (ARP) Used to dynamically discover the low level physical network hardware address that corresponds to the high level IP address for a given host. ARP is limited to physical network systems that support broadcast packets that can be heard by all hosts on the network. It is defined in RFC 826. Agent In the client-server model, the part of the system that performs information preparation and exchange on behalf of a client or server application. Alias A name, usually short and easy to remember, that is translated into another name, usually long and difficult to remember. Application A program that performs a function directly for a user. FTP, mail and Telnet clients are examples of network applications. Application Layer The top layer of the network protocol stack. The application layer is concerned with the semantics of work (e.g., formatting electronic mail messages). How to represent that data and how to reach the foreign node are issues for lower layers of the network. Asynchronous Transmission by individual bytes, not related to specific timing on the transmitting end. Asynchronous Transfer Mode (ATM) The ATM method for the dynamic allocation of bandwidth using a fixed-size packet (called a cell) with a length of 53-byte cells for a transmission unit. ATM uses cell switches, not bridge and router devices, to connect to remote endpoint devices. Authentication The verification of the identity of a person or process. AUI Attachment Unit Interface. The top level in a hierarchical network. Stub and transit networks which connect to the same backbone are guaranteed to be interconnected. Bandwidth Technically, the difference, in Hertz (Hz), between the highest and lowest frequencies of a transmission channel. However, as typically used, the amount of data that can be sent through a given communications circuit. Baseband A transmission medium through which digital signals are sent without complicated frequency shifting. In general, only one communication channel is available at any given time. Ethernet is an example of a baseband network. BOOTP The Bootstrap Protocol, described in RFCs 951 and 1084, is used for booting diskless nodes. Bridge A device which forwards traffic between network segments based on datalink layer information. These segments would have a common network layer address. Broadband A transmission medium capable of supporting a wide range of frequencies. It can carry multiple signals by dividing the total capacity of the medium into multiple, independent bandwidth channels, where each channel operates only on a specific range of frequencies. Broadcast A special type of multicast packet which all nodes on the network are always willing to receive. Broadcast Storm An incorrect packet broadcast onto a network that causes multiple hosts to respond all at once, typically with equally incorrect packets which causes the storm to grow exponentially in severity. A computed value which is dependent upon the contents of a packet. This value is sent along with the packet when it is transmitted. The receiving system computes a new checksum based upon the received data and compares this value with the one sent with th packet. If the two values are the same, the receiver has a high degree of confidence that the data was received correctly. Circuit Switching A communications paradigm in which a dedicated communication path is established between two hosts, and on which all packets travel. The telephone system is an example of a circuit switched network. Client A computer system or process that requests a service of another computer system or process. A workstation requesting the contents of a file from a file server is a client of the file server. Client-server Model A common way to describe the paradigm of many network protocols. Examples include the name-server/name-resolver relationship in DNS and the file-server/file-client relationship in NFS. Core Layer The Cisco hierarchical network design model defines the core layer as the high-speed switching backbone that should be designed to switch packets as fast as possible. These devices typically accept uplinks from “distribution layer” switches, connections to “border devices”. QUT’s core network layer consists of high speed switches / routers. Congestion Congestion occurs when the offered load exceeds the capacity of a data communication path. Connection-oriented The data communication method in which communication proceeds through three well-defined phases: connection establishment, data transfer, connection release. TCP is a connection-oriented protocol. Connectionless The data communication method in which communication occurs between hosts with no previous setup. Packets between two hosts may take different routes, as each is independent of the other. UDP is a connectionless protocol. A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network. DCE Data Circuit-terminating Equipment. DECnet A proprietary network protocol designed by Digital Equipment Corporation. The functionality of each Phase of the implementation, such as Phase IV and Phase V, is different. Default Route A routing table entry which is used to direct packets addressed to networks not explicitly listed in the routing table. Dialin PSTN/ISDN modem remote network access. Distribution Layer The Cisco hierarchical network design model defines the distribution layer of the network as the demarcation point between the access and core layers of the network. This layer includes LAN-based routers and layer 3 switches. Any switch that aggregate “access layer devices” back to the “core layer” is known as a “distribution device”. At QUT a mixture of layer2 and layer3 switches are used in the distribution layer to support access layer switches and servers / hosts requiring gigabit Ethernet connections. Domain Name System (DNS) The DNS is a general purpose distributed, replicated, data query service. The principal use is the lookup of host IP addresses based on host names. The style of host names now used in the Internet is called "domain name", because they are the style of names used to look up anything in the DNS. Some important domains are: .COM (commercial), .EDU (educational), .NET (network operations), .GOV (U.S. government), and .MIL (U.S. military). Most countries also have a domain. For example, .US (United States), .UK (United Kingdom), .AU (Australia). It is defined in STD 13, RFCs 1034 and 1035. DTE Data Terminal Equipment. A term for a digital carrier facility used to transmit a CEPT3 formatted digital signal at 34.368 megabits per second. Encapsulation The technique used by layered protocols in which a layer adds header information to the protocol data unit (PDU) from the layer above. As an example, in Internet terminology, a packet would contain a header from the physical layer, followed by a header from the network layer (IP), followed by a header from the transport layer (TCP), followed by the application protocol data. Encryption Encryption is the manipulation of a packet's data in order to prevent any but the intended recipient from reading that data. There are many types of data encryption, and they are the basis of network security. Ethernet A 10-Mb/s standard for LANs, initially developed by Xerox, and later refined by Digital, Intel and Xerox (DIX). All hosts are connected to either UTP cable or coaxial cable where they contend for network access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) paradigm. Ethernet Switch High performanace segmentation ethernet frame soluation, increses performance to 10 or 100 Mbps per end station and reduces segment traffic per station. Fibre Distributed Data Interface (FDDI) FDDI is a fibre optic backbone to connect LANs in a ring topology. File Transfer Protocol (FTP) A protocol which allows a user on one host to access, and transfer files to and from, another host over a network. Also, FTP is usually the name of the program the user invokes to execute the protocol. Fragment A piece of a packet. When a router is forwarding an IP packet to a network that has a maximum packet size smaller than the packet size, it is forced to break up that packet into multiple fragments. These fragments will be reassembled by the IP layer at the destination host. Fragmentation The IP process in which a packet is broken into smaller pieces to fit the requirements of a physical network over which the packet must pass. Frame A frame is a datalink layer "packet" which contains the header and trailer information required by the physical medium. That is, network layer packets are encapsulated to become frames. Fully Qualified Domain Name (FQDN) The FQDN is the full name of a system, rather than just its hostname. For example, "pigeon" is a hostname and "pigeon.qut.edu.au" is an FQDN. FO Fibre Optic cable, carrying Ethernet network traffic. FOT Fibre Optic Transceiver. The term "router" is now used in place of the original definition of "gateway". Currently, a gateway is a communications device/program which passes data between networks having similar functions but dissimilar implementations. This should not be confused with a protocol converter. By this definition, a router is a layer 3 (network layer) gateway, and a mail gateway is a layer 7 (application layer) gateway. The portion of a packet, preceding the actual data, containing source and destination addresses, and error checking and other fields. A header is also the part of an electronic mail message that precedes the body of a message and contains, among other things, the message originator, date and time. Heterogeneous Network A network running multiple network layer protocols. Hop A term used in routing. A path to a destination on a network is a series of hops, through routers, away from the origin. Host A computer that allows users to communicate with other host computers on a network. Individual users communicate by using application programs, such as electronic mail, Telnet and FTP. Hostname The name given to a machine. Hub A device connected to several other devices. In ARCnet, a hub is used to connect several computers together. In a message handling service, a hub is used for the transfer of messages across the network. While an internet is a network, the term "internet" is usually used to refer to a collection of networks interconnected with routers. The Internet is the largest internet in the world. Is a three level hierarchy composed of backbone networks (e.g., NSFNET, MILNET), mid-level networks, and stub networks. The Internet is a multiprotocol internet. Internet Address A IP address that uniquely identifies a node on an internet. An Internet address (capital "I"), uniquely identifies a node on the Internet. Internet Control Message Protocol (ICMP) ICMP is an extension to the Internet Protocol. It allows for the generation of error messages, test packets and informational messages related to IP. Internet Protocol (IP) The Internet Protocol, defined in STD 5, RFC 791, is the network layer for the TCP/IP Protocol Suite. It is a connectionless, best-effort packet switching protocol. Internetwork Packet eXchange (IPX) Novell's protocol used by Netware. A router with IPX routing can interconnect LANs so that Novell Netware clients and servers can communicate. IP Address The 32-bit address defined by the Internet Protocol in STD 5, RFC 791. It is usually represented in dotted decimal notation. E.g. the Internet number for the site cs.widener.edu is 147.31.254.130. Communication networks for computers may be organized as a set of more or less independent protocols, each in a different layer (also called level). The lowest layer governs direct host-to-host communication between the hardware at different hosts; the highest consists of user applications. Each layer builds on the layer beneath it. For each layer, programs at different hosts use protocols appropriate to the layer to communicate with each other. TCP/IP has five layers of protocols; OSI has seven. The advantages of different layers of protocols is that the methods of passing information from one layer to another are specified clearly as part of the protocol suite, and changes within a protocol layer are prevented from affecting the other layers. This greatly simplifies the task of designing and maintaining communication programs. Local Area Network (LAN) A data network intended to provide the ability to connect all the computers, terminals and peripherals etc on a single site or an area of only a few square kilometres or less. Because the network is known to cover only a small area, optimizations can be made in the network signal protocols that permit data rates up to 100Mb/s. The hardware address of a device connected to a shared media. MAN Metropolitan Area Network. Media Access Control (MAC) The lower portion of the datalink layer. The MAC differs for various physical media. Medium The material used to support the transmission of data. This can be copper wire, coaxial cable, optical fibre, or electromagnetic wave (as in microwave). Multicast A packet with a special destination address which multiple nodes on the network may be willing to receive. Multihomed Host A host which has more than one connection to a network. The host may send and receive data over any of the links but will not route traffic for other nodes. Multiplex The division of a single transmission medium into multiple logical channels supporting many simultaneous sessions. For example, one network may have simultaneous FTP, telnet, rlogin, and SMTP connections, all going at the same time. A computer network is a data communications system which interconnects computer systems at various different sites. Network Address The network portion of an IP address. For a class A network, the network address is the first byte of the IP address. For a class B network, the network address is the first two bytes of the IP address. For a class C network, the network address is the first three bytes of the IP address. In each case, the remainder is the host address. In the Internet, assigned network addresses are globally unique. Network Border The network border is defined as the part of the network where two autonomous network systems intersect. At QUT the devices used to inter-connect the University network border to network systems such as AARNet, Griffith University, Cooperative Research Centre and the KG High School as are known as “border devices”. The University’s network border usually consists of routers and firewalls. Network Layer The OSI layer that is responsible for routing, switching, and subnetwork access across the entire OSI environment. Network News Transfer Protocol (NNTP) A protocol, defined in RFC 977, for the distribution, inquiry, retrieval, and posting of news articles. Network Management HP Unix (Openview), Nortel Networks (Optivity) Unix based Network Management System. Network Time Protocol (NTP) A protocol that assures accurate local timekeeping with reference to radio and atomic clocks located on the Internet. This protocol is capable of synchronizing distributed clocks within milliseconds over long time periods. It is defined in STD 12, RFC 1119. Node An addressable device attached to a computer network. An octet is 8 bits. This term is used in networking, rather than byte, because some systems have bytes that are not 8 bits long. OSI Open Systems Interconnection. Abbreviation for "Private Automated Branch Exchange". Commonly also called a "PBX", or "Telephone Switch". Packet The unit of data sent across a network. "Packet" a generic term used to describe unit of data at all levels of the protocol stack, but it is most correctly used to describe application data units. Packet InterNet Groper (PING) A program used to test reachability of destinations by sending them an ICMP echo request and waiting for a reply. The term is used as a verb: "Ping host X to see if it is up!" Packet Switching A communications paradigm in which packets (messages) are individually routed between hosts, with no previously established communication path. Point-to-Point Protocol (PPP) The Point-to-Point Protocol, defined in RFC 1171, provides a method for transmitting packets over serial point-to-point links. Port A port is a transport layer demultiplexing value. Each application has a unique port number associated with it. Post Office Protocol (POP) A protocol designed to allow single user hosts to read mail from a server. There are three versions: POP, POP2, and POP3. Protocol Stack A layered set of protocols which work together to provide a set of network functions. Proxy The mechanism whereby one system "fronts for" another system in responding to protocol requests. Proxy systems are used in network management to avoid having to implement full protocol stacks in simple devices, such as modems. A device which propagates electrical signals from one cable to another. Request For Comments (RFC) The document series, begun in 1969, which describes the Internet suite of protocols and related experiments. Not all (in fact very few) RFCs describe Internet standards, but all Internet standards are written up as RFCs. The RFC series of documents is unusual in that the proposed protocols are forwarded by the Internet research and development community, acting on their own behalf, as opposed to the formally reviewed and standardized protocols that are promoted by organizations such as CCITT and ANSI. Router A device which forwards traffic between networks. The forwarding decision is based on network layer information and routing tables, often constructed by routing protocols. Routing The process of selecting the correct interface and next hop for a packet being forwarded. Routing Information Protocol (RIP) A distance vector, as opposed to link state, routing protocol. It is an Internet standard IGP defined in STD 34, RFC 1058 (updated by RFC 1388). A protocol used to run IP over serial lines, such as telephone circuits or RS-232 cables, interconnecting two systems. SLIP is defined in RFC 1055. Server A provider of resources (e.g., file servers and name servers). Simple Network Management Protocol (SNMP) The Internet standard protocol, defined in STD 15, RFC 1157, developed to manage nodes on an IP network. Subnet A portion of a network, which may be a physically independent network segment, which shares a network address with other portions of the network and is distinguished by a subnet number. A subnet is to a network what a network is to an internet. Subnet address The subnet portion of an IP address. In a subnetted network, the host portion of an IP address is split into a subnet portion and a host portion using an address (subnet) mask. Synchronous Data communications in which transmissions are sent at a fixed rate, with the sending and receiving devices synchronized. STM1 A term for a digital carrier facility used to transmit a formatted digital signal at 155 megabits per second. An AT&T term for a digital carrier facility used to transmit a DS-1 formatted digital signal at 1.544 megabits per second. T3 A term for a digital carrier facility used to transmit a DS-3 formatted digital signal at 44.746 megabits per second. TCP/IP Protocol Suite Transmission Control Protocol over Internet Protocol. This is a common shorthand which refers to the suite of transport and application protocols which runs over IP. See also: IP, ICMP, TCP, UDP, FTP, Telnet, SMTP, SNMP. Telnet Telnet is the Internet standard protocol for remote terminal connection service. It is defined in STD 8, RFC 854 and extended with options by many other RFCs. Terminal Server A device which connects many terminals to a LAN through one network connection. A terminal server can also connect many network users to its asynchronous ports for dial-out capabilities and printer access. TIMS Abbreviation for "Telephone Information Management System". This device performs Telephone Billing and Network Management functions for a PABX network. Token Ring A token ring network consists of a set of nodes serially connected by a transmission medium. Information is transferred sequentially, bit by bit, from one active node to the next. Topology A network topology shows the computers and the links between them. A network layer must stay abreast of the current network topology to be able to route packets to their final destination. Transceiver Transmitter-receiver. The physical device that connects a host interface to a local area network, such as Ethernet. Ethernet transceivers contain electronics that apply signals to the cable and sense collisions. Transmission Control Protocol (TCP) An Internet Standard transport layer protocol defined in STD 7, RFC 793. It is connection-oriented and stream-oriented, as opposed to UDP. See also: connection-oriented, stream-oriented, User Datagram Protocol. An Internet Standard transport layer protocol defined in STD 6, RFC 768. It is a connectionless protocol which adds a level of reliability and multiplexing to IP. Virtual Local Area Network (VLAN) VLANs are a way of partitioning traffic flows in a network such that each packet transmitted by an end-station is assigned to a VLAN. An end-station only receives all the multicast and broadcast traffic on the LANs to which it belongs, and an end-station receives unicast traffic addressed to it on the VLAN to which it belongs. A network used to interconnect many LANs and or WANs, using either Frame Relay, X.25, ISDN, ATM or Synchronous communications which can cover a intercampus or National and International large geographic area.
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