Communication and Network

Physical Connection

Twisted-pair Cable

Twisted pair cabling is a type of wiring in which two conductors 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. In anotehr definition, it is also a type of cable that consists of two independently insulated wires twisted around one another. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. While twisted-pair cable is used by older telephone networks and is the least expensive type of local-area network (LAN) cable, most networks contain some twisted-pair cabling at some point along the network. In balanced pair operation, the two wires carry equal and opposite signals and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally.

Coaxial Cable

Coaxial cable, or coax, is an electrical cable with an inner conductor surrounded by a tubular insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer, and finally covered with a thin insulating layer on the outside. It is also known as a type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference. Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks, such as Ethernet. Coaxial cable is used as a transmission line for radio frequency signals, in applications such as connecting radio transmitters and receivers with their antennas, computer network connections, and distributing cable television signals. Coaxial cable should not be confused with other shielded cable used for carrying lower frequency signals such as audio signals. Shielded cable is similar in that it consists of a central wire or wires surrounded by a tubular shield conductor, but it is not constructed with the precise conductor spacing needed to function efficiently as a radio frequency transmission line.

Fiber-optic Cable

A technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves. Fiber optics has several advantages over traditional metal communications lines:

• Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data.


• Fiber optic cables are less susceptible than metal cables to interference.


• Fiber optic cables are much thinner and lighter than metal wires.
  
• Data can be transmitted digitally rather than analogically.

Fiber optics is a particularly popular technology for local-area networks. In addition, telephone companies are steadily replacing traditional telephone lines with fiber optic cables.

Network Terms

Node

In communication networks, a node is a connection point, either a redistribution point or a communication endpoint. 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 is consequently not a node. A node can be a computer or some other device, such as a printer. Every node has a unique network address, sometimes called a Data Link Control (DLC) address or Media Access Control (MAC) address. In data communication, a physical network node may either be a data circuit-terminating equipment (DCE) such as a modem, hub, bridge or switch; or a data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer, for example a router, a workstation or a server.

Client

Client-server computing or networking is a distributed application architecture that partitions tasks or work loads between service providers (servers) and service requesters, called clients.Often clients and servers operate over a computer network on separate hardware. A server machine is a high-performance host that is running one or more server programs which share its resources with clients. A client is an application that runs on a personal computer or workstation and relies on a server to perform some operations. Standard networked functions such as email exchange, web access and database access, are based on the client-server model. The client-server model has become one of the central ideas of network computing. Specific types of clients include web browsers, email clients, and online chat client.

Server

A network server is a computer designed to process requests and deliver data to other (client) computers over a local network or the Internet. Examples include Web servers, proxy servers, and FTP servers. It is also a computer or device on a network that manages network resources. Servers are often dedicated, meaning that they perform no other tasks besides their server tasks. On multiprocessing operating systems, however, a single computer can execute several programs at once. A server in this case could refer to the program that is managing resources rather than the entire computer.

Hub

A network hub or repeater hub is a device for connecting multiple twisted pair or fiber optic. Hubs work at the physical layer (layer 1) of the OSI model. The device is thus a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. It is also known as a common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. Hubs also often come with a BNC and/or AUI connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. A network hub is a fairly unsophisticated broadcast device.

Network Interface Card (NIC)

A wireless network interface controller (WNIC) is a network card which connects to a radio-based computer network, unlike a regular network interface controller (NIC) which connects to a wire-based network such as token ring or ethernet. This card uses an antenna to communicate through microwaves. An Ethernet network interface card is installed in an available slot inside the computer. The NIC assigns a unique address called a MAC (media access control) to the machine. The MACs on the network are used to direct traffic between the computers. The back plate of the network interface card features a port that looks similar to a phone jack, but is slightly larger. This port accommodates an Ethernet cable, which resembles a thicker version of a standard telephone line. Ethernet cable must run from each network interface card to a central hub or switch.

Network Operating System (NOS)

A networking operating system is an operating system that contains components and programs that allow a computer on a network to serve requests from other computer for data and provide access to other resources such as printer and file systems. It is also an operating system that includes special functions for connecting computers and devices into a local-area network (LAN). Novell Netware, Artisoft's LANtastic, Microsoft Windows Server, and Windows NT are examples of network operating system.

Distributed Processing

A system consisting of a network of microcomputers performing certain functions and linked with a main computer used for more complex tasks. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal. A computer program that runs in a distributed system is called a distributed program, and distributed programming is the process of writing such programs. It also refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them. Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

Host Computer

Main or controlling computer connected to other computers or terminals to which it provides data or computing services via a network. It is similar to a server in a client-server architecture. It is also a computer system that is accessed by a user working at a remote location. The system that contains the data is called the host, while the computer at which the user sits is called the remote terminal. Another term to Host Computer is that it is a computer connected to a TCP/IP network, including the Internet.

Network Manager

NetworkManager is a software utility aimed at simplifying the use of computer networks on Linux and other Unix-like operating systems. NetworkManager is designed in two components: a service which manages connections and reports network changes, and a graphical desktop applet which allows the user to manipulate network connections. Both components are intended to be reasonably portable, and the applet is available to desktop environments which implement the Freedesktop.org System Tray Protocol, including GNOME, KDE and Xfce. As the components communicate via D-Bus, applications can be written to be “link-aware”, or replace the provided applet entirely. One example is KNetworkManager, a KDE frontend to NetworkManager developed by Novell for SUSE Linux.

Secondary Storage

Disk Caching

A portion of RAM used to speed up access to data on a disk. The RAM can be part of the disk drive itself (sometimes called a hard disk cache or buffer) or it can be general-purpose RAM in the computer that is reserved for use by the disk drive (sometimes called a soft disk cache). Hard disk caches are more effective, but they are also much more expensive, and therefore smaller. A soft disk cache works by storing the most recently accessed data in the RAM cache. When a program needs to access new data, the operating system first checks to see if the data is in the cache before reading it from the disk.

Redundant arrays of inexpensive disks (RAID)

RAID is a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for persona computers. RAID is also a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy. In simple words, RAID is a system of multiple hard drives for sharing or replicating data. RAID combines two or more physical hard disks into a single logical unit by using either special hardware or software. Hardware solutions often are designed to present themselves to the attached system as a single hard drive, so that the operating system would be unaware of the technical workings. There are three key concepts in RAID: mirroring, the copying of data to more than one disk; striping, the splitting of data across more than one disk; and error correction, where redundant data is stored to allow problems to be detected.

File Compression and Decompression

Data compression/File Compression is particularly useful in communications because it enables devices to transmit or store the same amount of data in fewer bits. Data compression or source coding is the process of encoding information using fewer bits than an un-encoded representation would use through use of specific encoding schemes.
Data compression is also widely used in backup utilities, spreadsheet applications, and database management systems. Certain types of data, such as bit-mapped graphics, can be compressed to a small fraction of their normal size. Compression is useful because it helps reduce the consumption of expensive resources, such as hard disk space or transmission bandwidth. On the downside, compressed data must be decompressed to be viewed (or heard), and this extra processing may be detrimental to some applications.

Input and Output

Magnetic-ink character recognition (MICR)

Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques. The use of magnetic printiallows the characters to be read reliably even if they have been overprinted or obscured by other marks, such as cancellation stamps.MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide. As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. MICR is the technology which allows the characters printed on the bottom of the check to be read by reader-sorter machines. The technology allows computers to read information (such as account numbers) off of printed documents.

Optical-character recognition

Optical-character recognition uses special preprinted characters that can be read by a light source and changed into machine-readable code. Optical-character recognition, usually abbreviated to OCR, is the mechanical or electronic recognition and translation of images of handwritten, typewritten or printed text into machine-editable text. Optical character recognition (using optical techniques such as mirrors and lenses) and digital character recognition (using scanners and computer algorithms) were originally considered separate fields. Optical-character recognition is a field of research in pattern recognition, artificial intelligence, and computer vision

Optical-mark recognition

Optical-mark recognition (OMR) is a process that allows certain marks or lines on special forms to be recognised by an optical mark reader, and input into a computer. It is also the process of capturing human-marked data from document forms such as surveys and tests. OMR is often used to score multiple-choice tests. Optical mark recognition (OMR) is the scanning of paper to detect the presence or absence of a mark in a predetermined position. Optical mark recognition has evolved from several other technologies.

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Dot Matrix Printer

A dot matrix printer or impact matrix printer is a type of computer printer with a print head that runs back and forth, or in an up and down motion, on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers. It is also a type of computer printer that uses tiny hammers in its print head to strike pins over an inked ribbon to form characters or images on paper, and is used mainly for multipart forms.

Plotter

A graphics printer that draws images with ink pens. It actually draws point-to-point lines directly from vector graphics files. The plotter was the first computer output device that could print graphics as well as accommodate full-size engineering and architectural drawings. Using different colored pens, it was also able to print in color long before inkjet printers became an alternative.

Photo Printer

A printer specialized for smaller prints such as 4x6" and 5x7". When first introduced in the mid-1990s, photo printers used dye sublimation for high quality printing because inkjet printing was not quite up to par. It is a printer (usually an inkjet printer) that is specifically designed to print high quality digital photos on photo paper. These printers usually have a very high number of nozzles and are capable of printing droplets as small as 1 picoliter.

Fax Machine

A device that sends and receives printed pages or images over telephone lines by converting them to and from electronic signals. It consists of an image scanner, a modem, and a printer. Digital fax machines first became popular in Japan, where they had a clear advantage over competing technologies like the teleprinter, since at the time it was faster to handwrite kanji than to type the characters. In many corporate environments, standalone fax machines have been replaced by "fax servers" and other computerized systems capable of receiving and storing incoming faxes electronically, and then routing them to users on paper or via an email . Such systems have the advantage of reducing costs by eliminating unnecessary printouts and reducing the number of inbound analog phone lines needed by an office.

Multifunctional Device

Multifunctional devices bring the worlds of copying, printing, finishing, and scanning together, all in one neat, efficient and cost-effective package. It is an office machine which incorporates the functionality of multiple devices in one, so as to have a smaller footprint in a home or small business setting or to provide centralized document management/distribution/production in a large-office setting. Two color MFPs of a similar speed will be in the same segment, despite having potentially very different feature sets, and therefore very different prices. From a marketing perspective, the manufacturer of the more expensive MFP would want to differentiate their product as much as possible to justify the price difference, and therefore the segment definition is avoided.