Lecture 2 glossary

Topologies and Signalling

Bit- Short for binary digit, the smallest unit of information on a machine. The term was first used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A single bit can hold only one of two values: 0 or 1. (1)

Kbps- Kilobit 1,024 bits. Data transfer rates are often measured in kilobits per second, abbreviated as Kbps. (1)

Mbps- Megabits per second:. Data rate of one Million bits per second. (1)

Gbps- Gigabits per second: One Billion (10 to the 9th) bits per second. (1)

Data Transfer Rate: The speed with which data can be transmitted from one device to another. Data rates are often measured in megabits (million bits) or megabytes (million bytes) per second. These are usually abbreviated as Mbps and MBps, respectively. (1)

Throughput- The amount of data transferred from one place to another or processed in a specified amount of time. Data transfer rates for disk drives and networks are measured in terms of throughput. Typically, throughputs are measured in Kbps, Mbps and Gbps. (1)

Ethernet- A LAN protocol developed by Xerox cooperation with dec and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. (1)

ANSI- Acronym for the American National Standards Institute. Founded in 1918, ANSI is a voluntary organization composed of over 1,300 members (including all the large computer companies) that creates standards for the computer industry. For example, ANSI C is a version of the C language that has been approved by the ANSI committee. To a large degree, all ANSI C compilers, regardless of which company produces them, should behave similarly.

In addition to programming languages, ANSI sets standards for a wide range of technical areas, from electrical specifications to communications protocols. For example, FDDI, the main set of protocols for sending data over fiber optic cables, is an ANSI standard. (1)

Topology-

The shape of a local-area network (LAN) or other communications system. There are three principal topologies used in LANs: buses, rings, and stars. (1)

bus topology- All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology. (1)

ring topology- All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances. (1)

star topology- All devices are connected to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub. (1)

BAUD- Pronounced bawd, the number of signaling elements that occur each second. The term is named after J.M.E. Baudot, the inventor of the Baudot telegraph code. At slow speeds, only one bit of information (signaling element) is encoded in each electrical change. The baud, therefore, indicates the number of bits per second that are transmitted. For example, 300 baud means that 300 bits are transmitted each second (abbreviated 300 bps ). Assuming asynchronous communication, which requires 10 bits per character, this translates to 30 characters per second (cps). For slow rates (below 1,200 baud), you can divide the baud by 10 to see how many characters per second are sent.

At higher speeds, it is possible to encode more than one bit in each electrical change. 4,800 baud may allow 9,600 bits to be sent each second. At high data transfer speeds, therefore, data transmission rates are usually expressed in bits per second (bps) rather than baud. For example, a 9,600 bps modem may operate at only 2,400 baud.

Tree Topology- LAN topology similar to a bus topology, except that tree networks can contain branches with multiple nodes. Transmissions from a station propagate the length of the medium and are received by all other stations. Compare with bus topology, ring topology, and star topology. (sourcce cisco)

Hybrid Topology - Network topology which combines more than one basic topology such as bus, ring, or star.

Physical Topology- Topology which is essentaily drawn as it is laid out rather than a logical topology which is symbolic of a particular network type or layout.

Logical Topology- A network topology which is symbolic of how a network or topology might be physically drawn. For instance, a large ring network might appear as a star network due to cable layout and cross-connects.

Star-Bus Topology- A hybrid topology which is a cross between a star and a bus.

Star-Ring Topology- A hybrid topology which is a cross between a ring and a star.

Signalling- Process of sending a transmission signal over a physical medium for purposes of communication. (Source Cisco)

Binary- Binary is the numbering system used by computers to represent information. Binary numbers consist of numbers represented by two values, 1s and 0s. Most computers store information in bytes (and multiples of bytes) that consists of 8 bits. These 8 bits can be combined to form 256 different values. The values represented by these 8 bits would be between 0 and 255. 0 would be represented by 00000000, decimal 1 by 00000001, decimal 2 by 00000010, decimal 3 by 00000011, decimal 4 by 00000100 and so forth until 255 which is represented by 11111111. (Source 3Com)

Analog Transmission- Signal transmission over wires or through the air in which information is conveyed through the variation of some combination of signal amplitude, frequency, and phase. (source Cisco)

Parallel Transmission- Method of data transmission in which the bits of a data character are transmitted simultaneously over a number of channels. Compare with serial transmission. (source Cisco)

Serial Transmission- Method of data transmission in which the bits of a data character are transmitted sequentially over a single channel. Compare with parallel transmission. (source Cisco)

Digital Signalling- Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they can distinguish between just two values, 0 and 1, or off and on. There is no simple way to represent all the values in between, such as 0.25. All data that a computer processes must be encoded digitally, as a series of zeroes and ones. (www.pcwebopedia.com)

Serial Port- A port, or interface, that can be used for serial communication, in which only 1 bit is transmitted at a time. Most serial ports on personal computers conform to the RS-232C or RS-422 standards. A serial port is a general-purpose interface that can be used for almost any type of device, including modems, mice, and printers (although most printers are connected to a parallel port). (www.pcwebopedia.com)

Parallel Port- A parallel interface for connecting an external device such as a printer. Most personal computers have both a parallel port and at least one serial port. On PCs, the parallel port uses a 25-pin connector (type DB-25) and is used to connect printers, computers and other devices that need relatively high bandwidth. It is often called a Centronics interface after the company that designed the original standard for parallel communication between a computer and printer. (www.pcwebopedia.com)

Sine Wave- The wave shown on electronic equipment such as an oscilloscope which demonstrates deviation in voltages or frequencies.

Voltage- A quantity measured as a signed difference between two points in an electrical circuit which, when divided by the resistance in Ohms between those points, gives the current flowing between those points in Amperes, according to Ohm's Law. Voltage is expressed as a signed number of Volts (V). (dictionary.com)

Frequency- Frequency is the measurement of time between waves measured in cycles per second (Hz.).

Modulation- Modulation is the manipulation of a higher frequency signal by a lower frequency signal.

Amplitude- The maximum absolute value reached by a voltage or current waveform. (dictionary.com)

Period- Period is the measurement of time between waves.

Synchronous Transmission- Term describing digital signals that are transmitted with precise clocking. Such signals have the same frequency, with individual characters encapsulated in control bits (called start bits and stop bits) that designate the beginning and end of each character. Compare with asynchronous transmission, isochronous transmission, and plesiochronous transmission. (Source Cisco)

Asyncronous Transmission- Term describing digital signals that are transmitted without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and end of each character. Compare with isochronous transmission, plesiochronous transmission, and synchronous transmission. (Source Cisco)

Daisy Chain- You create a daisy chain network by linking multiple devices together via a cabling system. In an AppleTalk network the daisy chain topology is created using phonenet connectors and twisted pair wiring (regular phone wire). A daisy chain configuration must be terminated at both ends using terminating resistors. (Source 3com)

Sources: (1) PC Webopedia (http://webopedia.internet.com)

(2) LAN Tutorial

(3) Introduction to Local Area Networks. Robert M. Thomas