Glossary of technical terms:
Access control: The means by which contention is resolved in a local area network. In an efficient network design, the means of access control will ensure that all users are provided with an effective transmission service. In regards to security, access control refers to exerting control over who can and cannot interact with a specific resource; similar to the way a key unlocks a door.
Analog signal: A signal that varies continuously in amplitude and/or frequency, and can have any value within reasonable limits. An example of analog speech is speech transmitted over a telephone line. Radios also use analog signals, but the trend for the future is to send signals in digital form.
Attenuation: The amount of signal lost as it travels through the cabling system.
AUI, AUI cable: Abbreviation for Attachment Unit Interface. An AUI cable is the cable used to connect a DTE to a transceiver. It is usually limited to 50 meters in length. An AUI is the 15-pin connector on an Ethernet card for connecting a network cable. A modified version called the AAUI (Apple Attachment Unit Interface) was used in conjunction with Apple Macintosh computers starting in 1991, but its use discontinued after 1998.
Backboard: Refers to a plywood panel mounted on the wall of a telecom closet. Used to mount the cross connect.
Balun: A transformer used to attach coaxial or twinaxial equipment to twisted pair cabling.
Bandwidth: The maximum capacity of a network channel. Usually expressed in bits per second (bps) or Hertz (Hz). The greater the bandwidth, the greater the volume of information the link can carry in a given time.
Baseband: A means of transmission in which data from different users is combined in a common path in a serial stream by time-sharing. Also refers to electronic data prior to any modification. It refers to analog or digital data before they are merged with other signals (multiplexed) or intermixed into a carrier wave (modulated). For example, the output of an analog microphone is baseband. Data being processed in the computer’s memory are baseband. In a digital wireless system, the digital data are considered baseband before they are modulated into a carrier frequency for over-the-air transmission.
Baud: A unit of signaling speed representing the number of discrete signal events per second and, depending on the encoding, can differ from the bit rate. At lower quantities, it is equivalent to one bit per second. However, at higher volumes, one baud can be made to represent more than one bit per second.
Bit: A contraction of binary digit. A fundamental way of expressing information in digital form using only the values 0 or 1. A byte consists of a string of eight consecutive bits and makes up the basic information-processing unit of a computer. Because a byte includes only an amount of information equivalent to one letter or one symbol (e.g., a comma), the processing and storage capacities of computer hardware are usually given in kilobytes (1,024 bytes), megabytes (1,048,576 bytes), gigabytes (about 1 billion bytes), or even terabytes (about 1 trillion bytes).
Bit rate: The number of bits per second being transferred in a data transmission. High data rates are measured in Mbps (megabits per second), lower rates are measured in kbps (kilobytes per second) or just bps (bits per second).
Block Encoding: Block encoding refers to a system whereby a group of data bits are encoded into a larger set of code bits. Block codes are part of a larger family of error-correcting codes that encode data in blocks. The main reason why the concept of block codes is so useful is that it allows coding theorists, mathematicians, and computer scientists to study the limitations of all block codes in a unified way. Such limitations often take the form of bounds that relate different parameters of the block code to each other, such as its rate and its ability to detect and correct errors. Examples of block codes are Reed–Solomon codes, Hamming codes, Hadamard codes, Expander codes, Golay codes, and Reed–Muller codes.
Blue Book: Informal name for one of the four standard references on the page-layout and graphics-control language PostScript. The other three official guides are known as the Green Book, the Red Book, and the White Book. When used in the context of LANs, blue book refers to the proprietary specifications for Ethernet issued jointly by Xerox, DEC, and Intel. It is now largely supplanted by the IEEE 802.3 standard.
BNC: BNC stands for Bayonet-Neill-Concelman. Describes a bayonet connector used in making thin Ethernet and cable television connections. BNCs are ideally suited for cable termination for miniature-to-subminiature coaxial cable (e.g., RG-58, 59, to RG-179, RG-316). It is used with radio, television, and other radio-frequency electronic equipment, test instruments, video signals, and was once a popular computer network connector.
Bridge: A device that governs the flow of traffic between networks or network segments and forwards packets between them. The bridge allows a message across if it is addressed to the other side; messages within the network are kept within the network, thus making the flow of traffic more efficient. Can also refer to a translation program that allows different computer programs to communicate and/or exchange data with other internal or external systems.
Broadcast: A transmission sent to many unspecified receivers at a time by means of a computer network, radio waves, or satellite. Broadcasting differs from multicasting and narrowcasting, in which a transmission is sent to a group of selected receivers. A broadcast is sent to everyone who has the equipment to receive it. On an Ethernet, a broadcast packet is where a copy of a given packet is given to all hosts attached to the network.
Bus: A set of conductors that connect the functional units in a computer. It is called a bus because it travels to all destinations. There are local busses that connect elements within the CPU and busses that connect the computer to external memory and peripherals. The bus width determines the speed of data transmission. Most personal computers use 32-bit busses both internally and externally. Internal busses are configured in parallel; there are also serial busses between computers in networks.
Bus Network: A type of network configuration where multiple nodes share access at the physical level. Each node must therefore wait until the medium (wire or bus) is free before sending its data packet. A bus network is the simplest and most commonly used network. It is similar to a fast food drive-thru and sometimes known as a Daisy-Chained network.
Category 3: A performance classification for twisted pair cables, connectors and systems. Specified to 16 MHz. Suitable for voice and data applications up to 10 Mbps.
Category 5: A performance classification for twisted pair cables, connectors and systems. Specified to 100 MHz. Suitable for voice and data applications up to 155 Mbps (possibly 1000 Mbps).
Category 5e: Also called Enhanced Category 5. A performance classification for twisted pair cables, connectors and systems. Specified to 100 MHz. Suitable for voice and data applications up to 1000 Mbps
Category 6: A performance classification for twisted pair cables, connectors and systems. Specified up to 250 MHz.
Channel (communications): In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.
Character: A character is any letter, number, space, punctuation mark, or symbol that can be typed on a computer. The word “computer,” for example, consists of eight characters. The phrase “Hi there.” takes up nine characters. Each character requires one byte (8 bits) of space; so “computer” takes up 8 bytes (64 bits). The list of characters that can be typed is defined by the ASCII and extended ASCII set.
Cheapernet: 10BASE2 (also known as Cheapernet, thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable (RG-58A/U or similar, as opposed to the thicker RG-8 cable used in 10BASE5 networks), terminated with BNC connectors. During the mid to late 1980s this was the dominant 10 Mbit/s Ethernet standard, but due to the immense demand for high speed networking, the low cost of Category 5 Ethernet cable, and the popularity of 802.11 wireless networks, both 10BASE2 and 10BASE5 have become increasingly obsolete, but still exist in many locations.
CI: Control In. AUI differential repair circuit, operating at pseudo ECL levels. The MAU drives a 10 MHz signal on the CI circuit to indicate to the DTE that or repeater that a collision has been detected on the network, that the MAU is the jabber state, or that an SQE Test from the MAU to the DTE is in progress.
Cluster:A computer cluster consists of a set of loosely connected computers that work together so that in many respects they can be viewed as a single system.
The components of a cluster are usually connected to each other through fast local area networks, each node (computer used as a server) running its own instance of an operating system. Computer clusters emerged as a result of convergence of a number of computing trends including the availability of low cost microprocessors, high speed networks, and software for high performance distributed computing. Clusters are usually deployed to improve performance and availability over that of a single computer, while typically being much more cost-effective than single computers of comparable speed or availability.
CMIP: Common managnement Information Protocol. The ISO defined transportprotocol to move management information through the network. Defined by ISEO/IEC 9595/6, Information Processing Systems-Open Systems Interconnection-Common Management Information Protocol Specification.
Coaxial cable: A type of electrical cable in which a single central wire that carries the signal is surrounded by insulation and then by a complete metal screen. Ethernet and cheapernet cables are coaxial, as are TV aerial cables. This type of construction is used because cable for high speed data transmission must have caefully controlled characteristics, including rejection of outside interference, and must not create interference itself.
Collision: The result of simultaneous transmission by two DTEs (Data Terminal Equipment) on a shared bus. After a collision has occurred, both DTEs must resend the data. The method that a DTE uses to determine whether a collision has occurred is called collision detection. A collision domain is a set of all stations and repeaters connected to a network where faithful detection of a collision can occur. A collision domain terminates at switch ports.
Concentrator: A general term frequently used instead of repeater. Typically, a concentrator supports more than one network protocl, such as 802.3/Ethernet as well as 802.5/Token Ring. The terms “hub”, “concentrator”, and “intelligent hub” are frequently used interchangeably to reference a multiport, multiprotocol device, capable of statistics gathering, fault monitoring and/or network management activites.
Contention: A condition that arises when two devices attempt to use a single resource at the same time. In these situations, access control is utilized.
Controller: The controller card, or simply “controller,” is a piece of hardware that acts as the interface between the motherboard and the other components of the computer. For example, hard drives, optical drives, printers, keyboards, and mice all require controllers to work. Most computers have all the necessary controllers built in the motherboard as chips, not full-sized cards. However, if you add additional components such as a SCSI hard drive, you may need to add a controller card as well. Controller cards are typically installed in one of the computer’s PCI slots. For Cheapernet, the controller card and the transceiver are generally combined.
CRC: A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents; on retrieval the calculation is repeated, and corrective action can be taken against presumed data corruption if the check values do not match.
CRCs are so called because the check (data verification) value is a redundancy (it adds no information to the message) and the algorithm is based on cyclic codes. CRCs are popular because they are simple to implement in binary hardware, easy to analyze mathematically, and particularly good at detecting common errors caused by noise in transmission channels. Because the check value has a fixed length, the function that generates it is occasionally used as a hash function. The CRC was invented by W. Wesley Peterson in 1961; the 32-bit polynomial used in the CRC function of Ethernet and many other standards is the work of several researchers and was published during 1975.
Cross connect: Connecting hardware used to patch between two groups of cables (horizontal to backbone, for example). AMP 110Connect XC.
Crossover Cable: A twisted-pair patch cable wired in a way as to route the transmit signals from one piece of equipment to the receive signals of another piece of equipment, and vice versa. This allows communications between two DTEs or two DCEs. The opposite of a crossover cable is the straight-through cable.
CSMA/CD: Abbreviation for Carrier Sense Multiple Access with Collision Detection. It is a means of access control in which all DTEs have equal acces to the network. If no transmissions are sensed on the network, a DTE may transmit. If two DTEs transmit simultaneously, each DTE invloved in the collision backs off and retransmits after a random delay period.
DA: Destination Address. The 48-bit field within the 802.3/Ehthernet packet format which identifies the physical address. The field immeidately follows the Preamble/Start Frame Delimiter, and precedes the Destination Address (DA) field. The 802.3 protocol supports indivudual, multicast and broadcast addressing.
Data Link Layer: Layer 2 of the 7 layer OSI reference model. This layer takes in data from the network layer and passes it on to the physical layer. The data link layer is responsible for transmitting and receiving frames. It ususally includes both the media acces control (MAC) and logical link control (LLC) layers.
Data Signal: A signal that can have two specific values (e.g., “on” or “off”, “high” or “low”), rather than varying continuously, like an analog signal. Data normally exists in this two-state (binary) form and is transmitted as a series of pulses of discrete size in which the transmission medium is switched rapidly between the high and low values. In formation may also be stored using this digital form, using bits.
Data rate: The speed, measured in measured in bits per second, that a particular network (or other applications) transmits data.
DCE: A data circuit-terminating equipment (DCE) is a device that sits between the data terminal equipment (DTE) and a data transmission circuit. It is also called data communications equipment or data carrier equipment. Usually, the DTE device is the terminal (or computer), and the DCE is a modem.
In a data station, the DCE performs functions such as signal conversion, coding, and line clocking and may be a part of the DTE or intermediate equipment. Interfacing equipment may be required to couple the data terminal equipment (DTE) into a transmission circuit or channel and from a transmission circuit or channel into the DTE.
DI: Data In. AUI differential pair circuit, operating at pseudo EECL levels. Data recievd by the MAU from either the media or the DO circuit (or its logical equivalent), is driven into the DI circuit for use by the DTE or repeater.
DO: Data Out. AUI differential pair circuit, operating at pseudo ECL levels. The DTE or repeater drives Manchester encoded data out on the DO circuit (or its logical equivalent), which is transmitted by the MAU over the physical media and the DI circuit.
DTE (data terminal equipment): A DTE is the functional unit of a data station that serves as a data source or a data sink and provides for the data communication control function to be performed in accordance with the link protocol.
The data terminal equipment may be a single piece of equipment or an interconnected subsystem of multiple pieces of equipment that perform all the required functions necessary to permit users to communicate. A user interacts with the DTE (e.g. through a human-machine interface), or the DTE may be the user.
Usually, the DTE device is the terminal (or a computer emulating a terminal), and the DCE is a modem or another carrier-owned device.
ECMA: ECMA International is an international, private (membership-based) non-profit standards organization for information and communication systems. It acquired its current name in 1994, when the European Computer Manufacturers Association (ECMA) changed its name to reflect the organization’s global reach and activities. As a consequence, the name is no longer considered an acronym and no longer uses full capitalization. The organization was originally founded in 1961 to standardize computer systems in Europe. Membership is open to large and small companies worldwide that produce, market or develop computer or communication systems, and have interest and experience in the areas addressed by the group’s technical bodies. It is located in Geneva.
Encoding: In communications and information processing, encoding is the process by which information from a source is converted into symbols to be communicated. Decoding is the reverse process, converting these code symbols back into information understandable by a receiver.
ENDEC: In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or data stream, either with the same or separate circuitry or algorithm. The combining of these names is a portmanteau. The general difference between an endec and a codec (compressor / decompressor) is that hardware is usually considered to be an endec, while software is considered to be the codec. Similarly, the word “encoding” is usually used for hardware, while “coding” is usually used in regard to software.
A device or program which uses a compression algorithm to create MPEG audio and/or video is often called an encoder, and one which plays back such files is a decoder. However, this is technically a codec, especially if performed in software.
Electronic mail, e-mail: Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the same time, in common with instant messaging. Today’s email systems are based on a store-and-forward model. Email servers accept, forward, deliver and store messages. Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to an email server, for as long as it takes to send or receive messages.
Error detection: In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels. Many communication channels are subject to channel noise, and thus errors may be introduced during transmission from the source to a receiver. Error detection techniques allow detecting such errors, while error correction enables reconstruction of the original data.
Ethernet:Ethernet is a family of computer networking technologies for local area networks (LANs). Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3. Ethernet has largely replaced competing wired LAN technologies.
The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair and fiber optic links in conjunction with hubs or switches. Data rates were periodically increased from the original 10 megabits per second, to 100 gigabits per second.
Systems communicating over Ethernet divide a stream of data into shorter pieces called frames. Each frame contains source and destination addresses and error-checking data so that damaged data can be detected and re-transmitted. As per the OSI model Ethernet provides services up to and including the data link layer.
Ethernet Terms (numerical):
10BASE-FB: 10 Mb/s Baseband Fiber Optic Backbone. Uses 802.3 protocol, dual fiber point-to-point cabling with synchronous signaling to provide an inter-repeater “backbone” link. No definite maximum node count, maximum fiber distance 2 km, depending on system configuration.
10BASE-FL: 10Mb/s Baseband Fiber Optic Link. Uses 802.3 protocol, dual fiber point-to-point cabling and repeaters to provide the network architecture. No defined maximum node count, maximum fiber distance 1-2 km, depending on system configuration.
10BASE-FP: 10Mb/s Baseband Fiber Optic Passive. Uses 802.3 protocol, point-to-point twisted pair cabling and repeaters to provide the network architecture. No defined maximum node count, maximum fiber distance 0.5 km, depending on system configuration.
Fast Ethernet: A version of the Ethernet that runs at 100 Mbps. Although 100 Mpbs is not “fast”, this reference is still used.
Fast Link Pulse (auto-negotiation): Autonegotiation is an Ethernet procedure by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control. In this process, the connected devices first share their capabilities regarding these parameters and then choose the highest performance transmission mode they both support. In the OSI model, autonegotiation resides in the physical layer. Autonegotiation was originally defined as an optional component in the fast Ethernet standard. It is backwards compatible with 10BASE-T. The protocol was significantly extended in the gigabit Ethernet standard, and is mandatory for 1000BASE-T gigabit Ethernet over copper.
Fan-Out: In digital electronics, the fan-out of a logic gate output is the number of gate inputs to which it is connected.
In most designs, logic gates are connected together to form more complex circuits. While no more than one logic gate output is connected to any single input, it is common for one output to be connected to several inputs. The technology used to implement logic gates usually allows a certain number of gate inputs to be wired directly together without additional interfacing circuitry. The maximum fan-out of an output measures its load-driving capability: it is the greatest number of inputs of gates of the same type to which the output can be safely connected.
FCS: Frame Check Sequence. A 4-byte field appended to the end of each 802.3/Ethernet frame. The field contains a 32-bit CRC, mathematically computed on the Destination Address, Source Address, Length/Type and Data/Pad fields (all the frame except the Preamble, SFD and FCS fields). The CRC is appended by the MAC transmit process and checked by the MAC receive process, and used to verify the integrity of the frame contents.
Fiber Optic Cable: A transmission medium that is replacing copper cables for inter-building connections, and that will become increasingly important for local data links. In a fiber optic transmission system, the data is carried by pulses of light along glass fibers. This means of transmission has much higher bandwidth than copper cables, and is less subject to distortion and interference.
File Server: In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files (such as documents, sound files, photographs, movies, images, databases, etc.) that can be accessed by the workstations that are attached to the same computer network. The term server highlights the role of the machine in the client–server scheme, where the clients are the workstations using the storage. A file server is not intended to perform computational tasks, and does not run programs on behalf of its clients. It is designed primarily to enable the storage and retrieval of data while the computation is carried out by the workstations. File servers are commonly found in schools and offices, where users use a LAN to connect their client computers.
File transfer: File transfer is a generic term for the act of transmitting files over a computer network like the Internet. There are numerous ways and protocols to transfer files over a network. Computers which provide a file transfer service are often called file servers. Depending on the client’s perspective the data transfer is called uploading or downloading. File transfer for the enterprise now increasingly is done with Managed file transfer.
There are 2 types of file transfers:
- Pull-based file transfers where the receiver initiates a file transmission request
- Push-based file transfers where the sender initiates a file transmission request
Firmware: In electronic systems and computing, firmware is the combination of read-only memory and program code and data stored in it. Typical examples of devices containing firmware are embedded systems, computers, computer peripherals, mobile phones, and digital cameras. The firmware contained in these devices provides the control program for the device. Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory. Changing the firmware of a device may rarely or never be done during its economic lifetime; some firmware memory devices are permanently installed and cannot be changed after manufacture. Common reasons for updating firmware include fixing bugs or adding features to the device. This may require physically changing ROM integrated circuits, or reprogramming flash memory with a special procedure. Firmware such as the ROM BIOS of a personal computer may contain only elementary basic functions of a device and may only provide services to higher-level software. Firmware such as the program of an embedded system may be the only program that will run on the system and provide all of its functions.
FOIRL: Fiber Optic Inter Repeateer Link. IEEE specification for inter repeater communications link, primarily aimed at significantly increasing the distance capabilities of an 802.3/Ethernet network. Defined in section 9.9 of ISO/IEC 8802-3:1990.
Gateway: In a communications network, a network node equipped for interfacing with another network that uses different protocols. A gateway may contain devices such as protocol translators, impedance matching devices, rate converters, fault isolators, or signal translators as necessary to provide system interoperability. It also requires the establishment of mutually acceptable administrative procedures between both networks.A protocol translation/mapping gateway interconnects networks with different network protocol technologies by performing the required protocol conversions. Gateways, also called protocol converters, can operate at any network layer. The activities of a gateway are more complex than that of the router or switch as it communicates using more than one protocol.
HIMIB: Hardware Implemented Management Information Base. The HIMIB device (Am79C987) effectively acts as a “management co-processor) to the IMR+ device, providing support for all hardware intensive Repeater Management functions. The HIMIB device incorporates
hardware registers which directly support the mandatory and optional attributes required to implement an IEEE 802.3 repeater MIB.
HMI: Hub Managementt Interface. A specification developed by Novell, Inc., which defines the MIB variables for a 10BASE-T repeater, as wwell as the driver independent protocol by which the variables are accessed in a Novell software environment.
HTTP: The Hypertext Transfer Protocol (HTTP) is an application protocol for for the World Wide Web.
Hypertext distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication is a multi-linear set of objects, building a network by using logical links (the so-called hyperlinks) between the nodes (e.g. text or words). HTTP is the protocol to exchange or transfer hypertext.
Hub: An Ethernet hub, active hub, network hub, repeater hub, multiport repeater or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. The device is a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision.
IEEE, IEEE 802: The Institute of Electrical and Electronics Engineers (IEEE, read I-Triple-E) is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence. It has more than 400,000 members in more than 160 countries, about 51.4% of whom reside in the United States. One of the IEEE technical committees, known as IEEE 802, is a major focus of activity in the preparation of standards for local aea networks.
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (often called TCP/IP, although not all applications use TCP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support email.
Internet Protocol: The Internet Protocol (IP) is the principal communications protocol used for relaying datagrams (also known as network packets) across an internetwork using the Internet Protocol Suite. Responsible for routing packets across network boundaries, it is the primary protocol that establishes the Internet.
IP is the primary protocol in the Internet Layer of the Internet Protocol Suite and has the task of delivering datagrams from the source host to the destination host solely based on the addresses. For this purpose, IP defines datagram structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram source and destination.
Jabber: A MAU is required to interrupt a station that is transmitting.
LAN: A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building using network media. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.
MAU: A Media Access Unit (MAU, also called Multistation Access Unit, MSAU) is a device to attach multiple network stations in a star topology in a token ring network, internally wired to connect the stations into a logical ring. The MAU contains relays to short out non-operating stations. Multiple MAUs can be connected into a larger ring through their Ring In/Ring Out connectors.
Modem: A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from light emitting diodes to radio. The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrical signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.
Multi-mode optical fiber (multimode fiber or MM fiber or fibre) is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Typical multimode links have data rates of 10 Mbit/s to 10 Gbit/s over link lengths of up to 600 meters (300 m for 10 Gbit/s) — more than sufficient for the majority of premises applications.
Multiplexer: In electronics, a multiplexer (or MUX) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output. Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. A multiplexer is also called a data selector. They are used in CCTV, and almost every business that has CCTV fitted, will own one of these.
An electronic multiplexer makes it possible for several signals to share one device or resource, for example one A/D converter or one communication line, instead of having one device per input signal.
Network: A network is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information. Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. Simply, more than one computer interconnected through a communication medium for information interchange is called a computer network.
Networks may be classified according to a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, and organizational scope.
Communications protocols define the rules and data formats for exchanging information in a computer network, and provide the basis for network programming. Well-known communications protocols include Ethernet, a hardware and link layer standard that is ubiquitous in local area networks, and the Internet protocol suite, which defines a set of protocols for internetworking, i.e. for data communication between multiple networks, as well as host-to-host data transfer, and application-specific data transmission formats.
7-layer OSI Model:
Network management: Refers to the activities, methods, procedures, and tools that pertain to the operation, administration, maintenance, and provisioning of networked systems.
Operation deals with keeping the network (and the services that the network provides) up and running smoothly. It includes monitoring the network to spot problems as soon as possible, ideally before users are affected.
Administration deals with keeping track of resources in the network and how they are assigned. It includes all the “housekeeping” that is necessary to keep the network under control.
Maintenance is concerned with performing repairs and upgrades—for example, when equipment must be replaced, when a router needs a patch for an operating system image, when a new switch is added to a network. Maintenance also involves corrective and preventive measures to make the managed network run “better”, such as adjusting device configuration parameters.
Provisioning is concerned with configuring resources in the network to support a given service. For example, this might include setting up the network so that a new customer can receive voice service.
Node: In communication networks, a node (Latin nodus, ‘knot’) is a connection point, either a redistribution point or a communication endpoint (some terminal equipment). The definition of a node depends on the network and protocol layer referred to. A physical network node is an active electronic device that is attached to a network, and is capable of sending, receiving, or forwarding information over a communications channel. A passive distribution point such as a distribution frame or patch panel is consequently not a node.
Packet: In computer networking, a packet is a formatted unit of data carried by a packet mode computer network. Computer communications links that do not support packets, such as traditional point-to-point telecommunications links, simply transmit data as a series of bytes, characters, or bits alone. When data is formatted into packets, the bitrate of the communication medium can be better shared among users than if the network were circuit switched.
Packet length: The sizze of a packet sent through a network, usually measured in bits or bytes. Some LANs have a fixed short packet length; other, including Ethernet, have a variable packet length that facilitatees the efficient transmission of files of data.
Plug compatible: A plug-compatible machine is one that has been designed to be backwards compatible with a prior machine. In particular, a new computer system that is plug-compatible has not only the same connectors and protocol interfaces to peripherals, but also runs the same CPU software as the old system. A plug compatible manufacturer or PCM is a company that makes such products.
The term may also be used to define replacement criteria for other components available from multiple sources. For example, a plug-compatible cooling fan may need to have not only the same physical size and shape, but also similar capability, run from the same voltage, use similar power, attach with a standard electrical connector, and have similar mounting arrangements. Some non-conforming units may be re-packaged or modified to meet plug-compatible requirements, as where an adapter plate is provided for mounting, or a different tool and instructions are supplied for installation, and these modifications would be reflected in the bill of materials for such components. Similar issues arise for computer system interfaces when competitors wish to offer an easy upgrade path.
Proprietary: The word propietary, when used in the context of LANs, describes a LAN that can only operate using the equipment of one specific vendor. This is in contrast to an open system.
Patch cable: A patch cable or patch cord is an electrical or optical cable used to connect (“patch-in”) one electronic or optical device to another for signal routing. Devices of different types (e.g., a switch connected to a computer, or a switch to a router) are connected with patch cords. Patch cords are usually produced in many different colors so as to be easily distinguishable, and are relatively short, perhaps no longer than two meters.
Preamble: An alternating “1, 0, 1, 0…”sequence at the start of each frame transmission. The pramble for 802.3 networks is defined as 7-bytes long, followed by a 1-byte SFD; whereas the preamble for Ethernet networks is defined as 62-bits long, with a 2-bit “Synch” character (henec both have an overall preamble/start delimiter length of 64-bits). When Manchester encoded, the preamble sequence produces a 5 MHz frequency at the start of each frame, which is used by a receiving station or repeater as a reference to decode the receive clock and data.
Repeater: An 802.3/Ethernet repeater in its most generic form is an “n” port device that supports the 802.3 protocol only. A repeater is used to extend the physical topology of a network, allowing two or more cable segments to be coupled together. No more than four repeaters are permitted between the end-to-end paths of two stations. When data is received on a single port, the repeater retransmits the incoming bit stream to all other ports, performing signal retiming and amplitude restoration. When data appears simultaneously on more than one port, the repeater transmits a collision to all ports, including the receiving ports. In addition, the repeater can isolate a port if it detects faults, such as an excessive number or duration of collisions, to prevent disruption of the rest of the network. In a 10BASE-T network, the repeater provides a central point of connectivity, ideally suited to the incorporation of statistics gathering and network administration functions.
Repeater Management: The generic term used to describe the 802.3 Supplements “Layer Management for 10 Mb/s Baseband Repeaters. The Repeater Management Standard defines the MIB variables for an 802.3 repeater.
Repeater MIB: The generic term used to describe RFC 1386, which defines the MIB variables and their encoding for use by SNMP.
RFC: Request For Comment. A specification administered and developed by the Internet community. The specifications are public domain, and detail the TCP/IP Internet protocol suite.
RMON MIB: Remote Network Monitoring Management Information Base. Defines the MIB attributes for a networking device, with detailed statistic
Router: A router is a device that forwards data packets between computer networks, creating an overlay inter-network. A router is connected to two or more data lines from different networks. When a data packet comes in on one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers perform the “traffic directing” functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the inter-network until it gets to its destination node.
Ring network: A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node – a ring. Data travels from node to node, with each node along the way handling every packet.
Because a ring topology provides only one pathway between any two nodes, ring networks may be disrupted by the failure of a single link. A node failure or cable break might isolate every node attached to the ring.
SA: Source Address. The 48-bit field within the 802.3/Ethernet packet format which identifies the sender’s unique physical address. The field immediately follows the DA, Destination Address.
Segment: One portion of the bus of an Ethernet LAN, consisting of standard Ethernet coaxial cable up to 500 meters long, or RG/58 Cheapernet Coaxial cable up to 185 meters in length.
SFD: Start of Frame Delimiter. The SFD immediately follows the alternating “1, 0, 1, 0…” preamble sequence. The SFD for 802.3 networks is defined as a 1-byte field consisting of the pattern “1, 0, 1, 0,1, 0, 1, 1” whereas for Ethernet networks a 2-bit pattern of “1, 1” at the end of a preamble signifies the “Synch” character (although the byte containing the SFD/Synch character is identical in both cases). The first but of the 802.3 frame (the Destination Address field) immediately follows the SFD.
SIA: Serial Interface Adapter. A Manchester Encoder/Decoder IC, which performs the Physical Signaling (PLS) sublayer functions of the IEEE 802.3 Standard. The device encodes data and clock from the MAC for transmission over the network, and drives the DO circuit of the AUI. It receives data from the network via the DI circuit of the AUI, extracts the data and clock into separate paths, and passes these back to the MAC
Software: Computer software, or just software, is a collection of computer programs and related data that provides the instructions for telling a computer what to do and how to do it. Software refers to one or more computer programs and data held in the storage of the computer for some reasons. In other words, software is a set of programs, procedures, algorithms and its documentation concerned with the operation of a data processing system. Program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software. The term was coined to contrast to the old term hardware (meaning physical devices). In contrast to hardware, software “cannot be touched”. Software is also sometimes used in a more narrow sense, meaning application software only. Sometimes the term includes data that has not traditionally been associated with computers, such as film, tapes, and records.
SNMP: Simple Network Management Protocol. The Internet specified transport protocol for the movement of management data in a heterogeneous work environment.
Snowflake: A LAN configuration in which a number of star configured sub-systems are interlinked. This topology is commonly used in fiber-optic and twisted pair networks.
SQE: Abbreviation for Software Quality Error. A signal quality error message is sent by trancievers (equipped with SQE) to the Ethernet controller where there are network faults, collisions on the network, and after the tranciever transmits data to the network. Transcievers with an SQE can not be used to connect repeaters to network segments. Also referred to as “heartbeat”, since the signal looks like a blip if observed on an oscilloscope.
Star: Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. This consists of a central node, to which all other nodes are connected; this central node provides a common connection point for all nodes through a hub. Thus, the hub and leaf nodes, and the transmission lines between them, form a graph with the topology of a star. If the central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time (i.e. to and from the central node) plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems.
Star network model:
Switch: In electrical engineering, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.
The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either “closed” meaning the contacts are touching and electricity can flow between them, or “open”, meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) can be either a “toggle” (flip switch for continuous “on” or “off”) or “momentary” (push-for “on” or push-for “off”) type.
Synch: Synchronization. The “Synch” immediately follows the alternating “1, 0, 1, 0…” preamble sequence in an Ethernet frame, and indicates the first bit of the frame (the Destination Address field) will follow immediately. The Synch for Ethernet networks is a 2-bit pattern of”1, 1” at the conclusion of the preamble.
TCP: The Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. TCP is the protocol used by major Internet applications such as the World Wide Web, email, remote administration and file transfer. Other applications, which do not require reliable data stream service, may use the User Datagram Protocol (UDP), which provides a datagram service that emphasizes reduced latency over reliability.
Terminal: Shorthand for “computer terminal”. A terminal normally consists of a visual display screen plus a keyboard for communicating with a computer. It may be a “dumb terminal”, in which case ot contains little or no processing power, or an intelligent terminal, that in varying degrees is able to carry out some of the functions of a computer. The greater the computing power of the terminal, the better its ability to make effective use of the local area network. The optimum terminal for networking is the personal computer that permints the building of distributed systems.
Termination: The “proper end” of a network segment which operates as a transmission line. Proper termination simulates an ideal transmission line by exacting matching the impendance of the medium. Improper termination, such as complete open circuit, a complete short, or non-matching resistance, causes signals on the medium to bounce off the impendance discontinuity. Such reflections usually result in a slower data rates and eventual data loss.
Thick-net: 10BASE5 (also known as thick ethernet or thicknet) was the original commercially available variant of Ethernet. For its physical layer it used cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, 0.375-inch (9.5 mm) diameter cable with an impedance of 50 ohms (Ω), a solid center conductor, a foam insulating filler, a shielding braid, and an outer jacket. The outer sheath was often yellow-to-orange/brown foam fluorinated ethylene propylene (for fire resistance) so it often is called “yellow cable”, “orange hose”, or sometimes humorously “frozen yellow garden hose”.
Thin-net: See Cheapernet
Token passing: A means of access control for LANs in which a node is allowed to transmit only when it is holding a password or token. The token is passed from node to node in accordance with set rules. In telecommunication, token passing is a channel access method where a signal called a token is passed between nodes that authorizes the node to communicate. The most well-known examples are token ring and ARCNET.
TPEX: Twisted Pair Ethernet Transceiver. A transceiver IC that converts the electrical signals of the AUI to those of the 10BASE-T Standard.
Transmission Line: In communications and electronic engineering, a transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that their wave nature must be taken into account. Transmission lines are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, and computer network connections.
Transparency: In telecommunications, transparency can refer to:
1. The property of an entity that allows another entity to pass through it without altering either of the entities.
2. The property that allows a transmission system or channel to accept, at its input, unmodified user information, and deliver corresponding user information at its output, unchanged in form or information content. The user information may be changed internally within the transmission system, but it is restored to its original form prior to the output without the involvement of the user.
3. The quality of a data communications system or device that uses a bit-oriented link protocol that does not depend on the bit sequence structure used by the data source.
Token ring: Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop.
Initially used only in IBM computers, it was eventually standardized with protocol IEEE 802.5.
The data transmission process goes as follows:
Empty information frames are continuously circulated on the ring.
When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.
The frame is then examined by each successive workstation. The workstation that identifies itself to be the destination for the message copies it from the frame and changes the token back to 0.
When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.
The frame continues to circulate as an “empty” frame, ready to be taken by a workstation when it has a message to send.
Twisted Pair: Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell. Becoming a popular transmission medium for LANs.
Type: A 2-byte field in the Ethernet frame, immediately following the Source Address field, and preceding the Data field, which defines the protocol type of the frame. The Type specification has no meaning at the MAC level, and is passed to higher level protocols. In the 802.3 frame, this field defines the protocol type of the frame.
V24: A standard interface connection providing cicuit conditions for data transmission. Many types of DTEs are designed to use this connection as a standard means of communication. Although providing quite high data rates, a single V24 channel uses much less bandwidth than is available from a local are network such as Ethernet; this allows the possibility of suing multiplexers for V24 transmission.
VDU (visual display unit): A monitor is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors use a cathode ray tube about as deep as the screen size.
Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and then computer monitors, has also changed from 4:3 to 16:9 (and 16:10).
Virual circuit: In telecommunications and computer networks, a virtual circuit (VC), synonymous with virtual connection and virtual channel, is a connection oriented communication service that is delivered by means of packet mode communication. After a connection or virtual circuit is established between two nodes or application processes, a bit stream or byte stream may be delivered between the nodes; a virtual circuit protocol allows higher level protocols to avoid dealing with the division of data into segments, packets, or frames.
Virtual circuit communication resembles circuit switching, since both are connection oriented, meaning that in both cases data is delivered in correct order, and signalling overhead is required during a connection establishment phase.
Wide Area Network: A Wide Area Network (WAN) is a telecommunication network that covers a broad area (i.e., any network that links across metropolitan, regional, or national boundaries). Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence this mode of telecommunication allows a business to effectively carry out its daily function regardless of location.
This is in contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs) which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively.
Work Area: Where the users telecommunications equipment resides. The part of the cabling system between the outlet and the equipment.
World Wide Web: The World Wide Web (abbreviated as WWW or W3, commonly known as the Web or the “Information Superhighway”), is a system of interlinked hypertext documents accessed via the Internet. Not to be confused with the actual Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia, and navigate between them via hyperlinks.
Using concepts from his earlier hypertext systems like ENQUIRE, British engineer and computer scientist Sir Tim Berners-Lee, now Director of the World Wide Web Consortium (W3C), wrote a proposal in March 1989 for what would eventually become the World Wide Web. At CERN, a European research organization near Geneva situated on Swiss and French soil, Berners-Lee and Belgian computer scientist Robert Cailliau proposed in 1990 to use hypertext “… to link and access information of various kinds as a web of nodes in which the user can browse at will”, and they publicly introduced the project in December.
Zone cabling: An architectural concept which splits the horizontal cabling into two sections. Eliminates the need to replace the entire horizontal cable in moves, adds, and changes.