Computer Network Assignment A134614 & A134617

Introduction
A computer network allows sharing of resources and information among interconnected devices. In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first computer network in the world. Development of the network began in 1969, based on designs developed during the 1960s.

Purpose
Computer networks can be used for several purposes:
 * Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
 * Sharing hardware. In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.
 * Sharing files, data, and information. In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
 * Sharing software. Users connected to a network may run application programs on remote computers.

Background
Explosive Internet growth in the late 1990s dramatically affected the evolution of computer networking. Some new network technologies and initiatives boomed but quickly faded into oblivion. Others have stood the test of time.

Below I've highlighted my picks for the top movers and shakers in the history of computer networking during this stretch of "Internet time."

Home Broadband
High-speed home networking struggled to get off the ground in 1997 and 1998. Cable modem was the first broadband option available to many, but only a few hundred thousand subscribed to Internet cable in that first year. In 1999, competition from DSL kicked in, but DSL availability remained quite limited at first. The expected competition from satellite services did not emerge until later, and even today, satellite services remain a distant third in the home broadband market.

It took until 2001 for home broadband to enter mainstream usage and begin growing at a faster rate than Internet dial-up services. Although the networking industry continues to promote broadband as the future pathway to new and exciting Internet applications, tens of millions of U.S. households remain on dial-up. The spirited battle between cable and DSL also continues.

Although many in the industry remain disappointed in the slow adoption rate of home broadband, initial concerns over a) reliability of DSL, b) security of cable modem, c) broadband accessiblity in rural areas, and d) viability of the broadband service providers, have all largely been addressed. The future of home broadband appears quite promising. === Napster and Peer to Peer===

A 19 year-old student named Shawn Fanning dropped out of college in 1999 to build a piece of software called Napster. Within a few months, Napster became one of the most popular software applications of all time. People all over the world regularly logged into Napster to freely swap music files in the MP3 digital format. Some proclaimed Napster "revolutionary." It certainly created a large stir in the industry press.

Users invested large amounts of time and energy in Napster. They also consumed big chunks of network bandwidth. Some universities and businesses reacted by banning or blocking Napster to keep their networks stable, generating even more controversy.

Napster was built using a network design technique called peer-to-peer (P2P). Though peer networking had existed for decades, Napster generated a new wave of interest in P2P. Many startup and some established companies jumped on the P2P bandwagon, activitely promoting new or rehashed, generally unproven business opportunities based on this technology.

Both Napster and corporate P2P have rapidly faded into obscurity. Napster faced the wrath of the music industry establishment, who claimed that open music file sharing violated copyright laws. The legal process moved slowly, but eventually the courts shut Napster down. Corporate interest in P2P suffered a similar fate. The allure of Napster proved to be its openness, not its network architecture, and initiatives to create comparable paid services have all stuggled mightily to get off the ground. === Apache===

Score one for the Open Source movement. Since 1996, and despite formidable competition from the likes of Microsoft, Apache has remained the world's most popular Web server by a wide margin. Web site owners frequently choose Apache for its reliability, performance and zero cost. Apache works well not only for "mom-and-pop" sites but also supports some of the busiest Web sites on the Internet.

Today, Apache has expanded well beyond its original roots as a mere HTTP server to support numerous new Internet technologies including Web Services. Apache should remain a key Internet technology for years to come.

Benefits
File Sharing: Networks offer a quick and easy way to share files directly. Instead of using a disk or USB key to carry files from one computer or office to another, you can share files directly using a network.

Software Cost and Management: Many popular software products are available for networks at a substantial savings in comparison to buying individually licensed copied for all of your computers. You can also load software on only the file server which saves time compared to installing and tracking files on independent computers. Upgrades are also easier because changes only have to be done once on the file server instead of on individual workstations.

Security: Specific directories can be password protected to limit access to authorized users. Also, files and programs on a network can be designated as "copy inhibit" so you don’t have to worry about the illegal copying of programs.

Resource Sharing: All computers in the network can share resources such as printers, fax machines, modems, and scanners.

Communication: Even outside of the internet, those on the network can communicate with each other via electronic mail over the network system. When connected to the internet, network users can communicate with people around the world via the network.

Flexible Access: Networks allow their users to access files from computers throughout the network. This means that a user can begin work on a project on one computer and finish up on another. Multiple users can also collaborate on the same project through the network.

Workgroup Computing: Workgroup software like Microsoft BackOffice enables many users to contribute to a document concurrently. This allows for interactive teamwork.

What Is Network Classification
The following list presents categories used for classifying networks.

Connection method
Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet, wireless LAN, HomePNA, power line communication or G.hn.

Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

Wired technologies

 * Twisted pair wire is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 100 million bits per second.
 * Coaxial cable is widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
 * Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire.[citation needed]

Wireless technologies

 * Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
 * Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
 * Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
 * Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.
 * Infrared communication, which can transmit signals between devices within small distances not more than 10 meters peer to peer or ( face to face ) without any body in the line of transmitting.

Scale
Networks are often classified as local area network (LAN), wide area network (WAN), metropolitan area network (MAN), personal area network (PAN), virtual private network (VPN), campus area network (CAN), storage area network (SAN), and others, depending on their scale, scope and purpose, e.g., controller area network (CAN) usage, trust level, and access right often differ between these types of networks. LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations, such as a building, while WANs may connect physically separate parts of an organization and may include connections to third parties.

Functional relationship (network architecture)
Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., active networking, client–server and peer-to-peer (workgroup) architecture.

Network topology
Main article: Network topologyComputer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

Two Types of Networks Base On Physical Scope
Common types of computer networks may be identified by their scale.

Local area network
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).[2] Typical library network, in a branching tree topology and controlled access to resourcesAll interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[3]

Personal area network
A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[4] A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

Home area network
A home area network (HAN) is a residential LAN which is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a CATV or Digital Subscriber Line (DSL) provider. It can also be referred as an office area network (OAN).

Wide area network
A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

Campus network
A campus network is a computer network made up of an interconnection of local area networks (LAN's) within a limited geographical area. The networking equipments (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).

In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls.

Metropolitan area network
A Metropolitan area network is a large computer network that usually spans a city or a large campus. Sample EPN made of Frame relay WAN connections and dialup remote access.Sample VPN used to interconnect 3 offices and remote users====Enterprise private network==== An enterprise private network is a network build by an enterprise to interconnect various company sites, e.g., production sites, head offices, remote offices, shops, in order to share computer resources.

Virtual private network
A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.

A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.

Internetwork
An internetwork is the connection of two or more private computer networks via a common routing technology (OSI Layer 3) using routers. The Internet is an aggregation of many internetworks, hence its name was shortened to Internet.

Global area network
A global area network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.[5]

Internet
The Internet is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).

Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Intranets and extranets
Intranets and extranets are parts or extensions of a computer network, usually a local area network.

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered trusted from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Overlay network
An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. A sample overlay network: IP over SONET over OpticalFor example, many peer-to-peer networks are overlay networks because they are organized as nodes of a virtual system of links run on top of the Internet. The Internet was initially built as an overlay on the telephone network .[6]

Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using modem, before any data network existed.

Nowadays the Internet is the basis for many overlaid networks that can be constructed to permit routing of messages to destinations not specified by an IP address. For example, distributed hash tables can be used to route messages to a node having a specific logical address, whose IP address is not known in advance.

Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast have not seen wide acceptance largely because they require modification of all routers in the network.[citation needed] On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes a message traverses before reaching its destination.

For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes End System Multicast and Overcast for multicast; RON (Resilient Overlay Network) for resilient routing; and OverQoS for quality of service guarantees, among others

Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber").

Network interface cards
A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.

Repeaters
A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. Repeaters work on the Physical Layer of the OSI model.

Hubs
A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.[7] It works on the Physical Layer of the OSI model.

Bridges
A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:
 * Local bridges: Directly connect local area networks (LANs)
 * Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
 * Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Switches
A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.[8] A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches.[9] Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier).

Routers
A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data).

Conclusion
Networked computing has evolved from networks connecting computers and distributed computing through thin-client network computing in the 1980s and 1990s to Internet computing today. Centralized computing--which started with mainframes at the outset of the computing evolution, evolved to PCs, and lasted up to the 1980s--focused mainly on automating existing processes. This approach gave way as applications and systems evolved to the client-server model and the distributed computing model. The client-server model allowed for the creation of server applications responsible for the storage, analysis, and sorting of large amounts of data on central data servers, with connected workstations responsible only for front-end client applications capable of running queries, producing reports, and adding new records. Distributed computing meant that dedicated file servers also could be used throughout an internal Local-Area Network (LAN), each supporting a single application, such as e-mail, facsimile, data storage, graphics storage, or documentation storage. Computers, sometimes using different operating systems, could store different components of a single application, such as a spellchecker and thesaurus stored on different computers. Printers and other peripherals connected to the LAN offered users shared access over the network. Network monitoring and backups offered a high degree of data security and integrity. Personal computing entered a new era of productivity as spreadsheets, database programs, and word processors came increasingly into use at personal workstations.

The concept of network computing had its origins in 1995 with Oracle Corporation's concept of full-service client-server computing, where individual computers would rely on central servers on an internal network for all applications, databases, and information. Desktops would be minimally equipped with application-specific thin clients intended primarily to communicate with servers that would be responsible for all data processing. (In contrast a fat client would comprise a stand-alone PC workstation fully equipped with all requisite applications.) This model of network computing allows for lower costs of installation, security, and maintenance, since databases and applications would need to be maintained only on the central server, not at every workstation. This model has been found particularly useful for task-oriented professionals in engineering, medicine, accounting, and real-estate focused on content rather than technology, as well as in back-office operations supported by clerical and sales staff. One disadvantage to this model is that as clients increase in number, servers need to be upgraded given the additional computing burden placed on them, thus raising infrastructure and maintenance costs.

Networked computing has evolved with the advent and progress of the Internet to mean Internet computing. This means that computers linked over the Internet would access large central servers outfitted with pre-packaged server software and Internet database applications for all processing purposes. Oracle8i, developed by Oracle Corporation to replace thin-client computing in 1998, offers such a platform; it functions as an Internet database that supports Java, and it can consolidate data, Java objects, and Windows files. Java is important because it is being used as a foundation to develop interactive, real-time exchange of information by allowing dynamic querying of databases and managing logical workflow processing. Java applets and servlets, which are compact Java programs supported and run by larger applications such as the major Internet browsers (e.g., Netscape and Explorer) are increasingly being used to streamline online banking, interactive trading, investment planning, and online purchasing. Through the use of Java applets and servlets Web users need not download whole workflow applications and can thereby save space, memory, and hardware wear-and-tear at their desktops. In this model, computing is focused on facilitating the search and dissemination of information. Applications are distributed across the network, which means that various functions can be accessed through the network as though they were stand-alone components, dynamically loaded and discarded when used.

Internet computing also means that business data is consolidated onto large servers for global Internet access, easy management, and speedier business application usage. Remote access computing is supported through remote access servers and concentrators. The Internet computing model is valuable to businesses because it can lower computing costs without the complexity of general-purpose operating systems. Computers with different operating systems would utilize Internet protocols as they accessed, computed, and communicated over the Internet. This model is thought to combine the best of the mainframe and client-server worlds by centralizing backups and offering users an intuitive graphical interface. In effect, client-server computing would expand to allow computing via TCP/IP over the Internet, allowing the use of different systems and platforms as long as a Web browser with a graphical interface provided a point of entry for a Web user. Additionally, mobile and remote computing becomes possible in this model, with all users required only to have access to the Internet and a Web browser installed on their machines.

In fact, the trend toward mobile and other computing devices is expected to change the profile of Internet computing in the next 10 years, with an increase in the usage of handhelds, wireless, and miniature "wearable" computers. Increased reliance on Internet computing will lead to data storage, synchronization, and scheduling being consolidated at centralized server farms that connect the corporate office and remote workers through broadband links. The concept of building hard-wired applications for functions such as inventory and accounting will evolve into a more dynamic reliance on toolkits for a particular task, as is already evident in the proliferation of shareware, freeware, and discountware on the Internet. More than ever before, a menu of software tools is now available to complete any project. These tools, while occasionally downloaded to the desktop, are increasingly expected to reside on the network.

Futurists predict that PCs will soon be replaced by network computers, Internet appliances (from telephone-like devices to televisions), and non-desktop computers, such as enterprise servers and wearable computers. As business transactions increasingly take place online, issues such as security, authentication, and quality of service (QoS) are expected to be resolved. Constant wireless connectivity and virtual private networks will allow users to be connected anytime, anywhere to their corporate nets over the Internet. As wireless communications expands, the convergence of video, voice, and data will allow users to download books, movies, television, and radio signals to their portables over broadband wireless connections. Computers will not only be everywhere, they will be held centrally on a network and controlled remotely. You could go to work, connect to your home server and control devices such as security cameras, motion detectors, lights, alarm clocks, heating and cooling systems, refrigerators, microwaves, PCs, televisions, and VCRs remotely.

Reference

 * 1) Chris Sutton. "Internet Began 35 Years Ago at UCLA with First Message Ever Sent Between Two Computers". UCLA. Archived from the original on 2008-03-08.
 * 2) New global standard for fully networked home, ITU-T Press Release
 * 3) IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force
 * 4) http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci546288,00.html
 * 5) Moble Broadband Wireless connections (MBWA)
 * 6) D. Andersen, H. Balakrishnan, M. Kaashoek, and R. Morris. Resilient Overlay Networks. In Proc. ACM SOSP, Oct. 2001.
 * 7) Pountain, Dick (2001). The New Penguin Dictionary of Computing. New York: Penguin Books. ISBN 0-14-051-4376.
 * 8) "Define switch.". www.webopedia.com. Retrieved 2008-04-08.
 * 9) "Basic Components of a Local Area Network (LAN)". NetworkBits.net. Retrieved 2008-04-08.