NetworksConnecting Two or More Computers makes a Computer Network to ShareResources.In Information Technology, a Network is a series of points or nodes nodesinterconnected by communication paths. Networks can interconnect with other pathsnetworks and contain subnetworks. TopologyA topology (from Greek topos meaning place) is a description of any kind of localityin terms of its layout. In communication networks, a topology is a usually schematicdescription of the arrangement of a network, including its nodes and connecting networklines. There are two ways of defining network geometry: the Physical topology andthe Logical (or signal) topology. topologyThe physical topology of a network is the actual geometric layout of workstations.There are several common physical topologies, as described below and as shown inthe illustration.In the bus network topology, every workstation is connected to a main cablecalled the bus. Therefore, in effect, each workstation is directly connected to everyother workstation in the network.
In the star network topology, there is a central computer or server to which allthe workstations are directly connected. Every workstation is indirectly connectedto every other through the central computer.In the ring network topology, the workstations are connected in a closed loopconfiguration. Adjacent pairs of workstations are directly connected. Other pairs ofworkstations are indirectly connected, the data passing through one or moreintermediate nodes.A variation of the ring network topology is known as the Token Ring. In thisscheme, the signal travels in only one direction or senses around the ring, carriedby a so-called token from node to node.The mesh network topology employs either of two schemes, called full mesh andpartial mesh. In the full mesh topology, each workstation is connected directly toeach of the others. In the partial mesh topology, some workstations areconnected to all the others, and some are connected only to those other nodeswith which they exchange the most data.The tree network topology uses two or more star networks connected together.The central computers of the star networks are connected to a main bus. Thus, a treenetwork is a bus network of star networks.Logical (or signal) topology refers to the nature of the paths the signals follow fromnode to node. In many instances, the logical topology is the same as the physicaltopology. But this is not always the case. For example, some networks are physicallylaid out in a star configuration, but they operate logically as bus or ring networks.Network Types (Area): 1-LAN 2-MAN 3-WAN 4-Internet 5-Intranet 6-Extranet1- Local Area Network (LAN):A local area network (LAN) is a group of computers and associated devices thatshare a common communications line or wireless link and typically share theresources of a single processor or server within a small geographic area (forexample, within an office building). Usually, the server has applications and datastorage that are shared in common by multiple computer users. A local area networkmay serve as few as two or three users (for example, in a home network) or as manyas thousands of users (for example, in an FDDI network).Major local area network technologies are:EthernetToken RingFDDI 2
Ethernet is by far the most commonly used LAN technology. A number ofcorporations use the Token Ring technology. FDDI is sometimes used as a backboneLAN interconnecting Ethernet or Token Ring LANs. Another LAN technology,ARCNET, once the most commonly installed LAN technology, is still used in theindustrial automation industry.Typically, a suite of application programs can be kept on the LAN server. Users whoneed an application frequently can download it once and then run it from their localhard disk. Users can order printing and other services as needed through applicationsrun on the LAN server. A user can share files with others at the LAN server; read andwrite access is maintained by a LAN administrator. A LAN server may also be usedas a Web server if safeguards are taken to secure internal applications and data fromoutside access.In some situations, a wireless LAN may be preferable to a wired LAN because it ischeaper to install and maintain.2-Meropolitan Area Network (MAN):A metropolitan area network (MAN) is a network that interconnects users withcomputer resources in a geographic area or region larger than that covered by even alarge local area network (LAN) but smaller than the area covered by a wide areanetwork (WAN). The term is applied to the interconnection of networks in a cityinto a single larger network (which may then also offer efficient connection to awide area network). It is also used to mean the interconnection of several local areanetworks by bridging them with backbone lines. The latter usage is also sometimesreferred to as a campus network.Examples of metropolitan area networks of various sizes can be found in themetropolitan areas of London, England; Lodz, Poland; and Geneva, Switzerland.Large universities also sometimes use the term to describe their networks. A recenttrend is the installation of wireless MANs.3-Wide Area Network (WAN):A wide area network (WAN) is a geographically dispersed telecommunicationsnetwork …Network that connecting Networks between countries of large cities.4-Internet: The Internet, sometimes called simply "the Net," is a worldwidesystem of computer networks - a network of networks in which users at any onecomputer can, if they have permission, get information from any other computer (andsometimes talk directly to users at other computers). It was conceived by theAdvanced Research Projects Agency (ARPA) of the U.S. government (Army) in1969 and was first known as the ARPANET. The original aim was to create anetwork that would allow users of a research computer at one university to be able to"talk to" research computers at other universities. A side benefit of ARPANets designwas that, because messages could be routed or rerouted in more than one direction,the network could continue to function even if parts of it were destroyed in the eventof a military attack or other disaster. 3
Today, the Internet is a public, cooperative, and self-sustaining facility accessible tohundreds of millions of people worldwide. Physically, the Internet uses a portion ofthe total resources of the currently existing public telecommunication networks.Technically, what distinguishes the Internet is its use of a set of protocols called TCP/IP (for Transmission Control Protocol/Internet Protocol). Two recent adaptations ofInternet technology, the intranet and the extranet, also make use of the TCP/IPprotocol.For many Internet users, electronic mail (e-mail) has practically replaced the PostalService for short written transactions. Electronic mail is the most widely usedapplication on the Net. You can also carry on live "conversations" with othercomputer users, using Internet Relay Chat (IRC). More recently, Internet telephonyhardware and software allows real-time voice conversations.The most widely used part of the Internet is the World Wide Web (often abbreviated"WWW" or called "the Web"). Its outstanding feature is hypertext, a method ofinstant cross-referencing. In most Web sites, certain words or phrases appear in text ofa different color than the rest; often this text is also underlined. When you select oneof these words or phrases, you will be transferred to the site or page that is relevant tothis word or phrase. Sometimes there are buttons, images, or portions of images thatare "clickable." If you move the pointer over a spot on a Web site and the pointerchanges into a hand, this indicates that you can click and be transferred to anothersite.Using the Web, you have access to millions of pages of information. Web browsing isdone with a Web browser, the most popular of which are Microsoft Internet Explorerand Netscape Navigator. The appearance of a particular Web site may vary slightlydepending on the browser you use. Also, later versions of a particular browser areable to render more "bells and whistles" such as animation, virtual reality, sound, andmusic files, than earlier versions.5- Intranet: An intranet is a private network that is contained within anenterprise. It may consist of many interlinked local area networks and also use leasedlines in the wide area network. Typically, an intranet includes connections throughone or more gateway computers to the outside Internet. The main purpose of anintranet is to share company information and computing resources amongemployees. An intranet can also be used to facilitate working in groups and forteleconferences.6- Extranet: An extranet is a private network that uses Internet technology andthe public telecommunication system to securely share part of a businesssinformation or operations with suppliers, vendors, partners, customers, or otherbusinesses. An extranet can be viewed as part of a companys intranet that isextended to users outside the company. It has also been described as a "state ofmind" in which the Internet is perceived as a way to do business with other companiesas well as to sell products to customers. 4
Networks Hardware• BUS: In general, the term is used in two somewhat different contexts: (1) A bus is a network topology or circuit arrangement in which all devices are attached to a line directly and all signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it. (2) In a computer, a bus is the data path on the computers motherboard that interconnects the microprocessor with attachments to the motherboard in expansion slots (such as hard disk drives, CD-ROM drives, and graphics adapters).• Backbone: A backbone is a larger transmission line that carries data gathered from smaller lines that interconnect with it. 1) At the local level, a backbone is a line or set of lines that local area networks connect to for a wide area network connection or within a local area network to span distances efficiently (for example, between buildings). 2) On the Internet or other wide area network, a backbone is a set of paths that local or regional networks connect to for long-distance interconnection. The connection points are known as network nodes or telecommunication data switching exchanges (DSEs).• Bridge: In telecommunication networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or Token Ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs). In bridging networks, computer or node addresses have no specific relationship to location. For this reason, messages are sent out to every address on the network and accepted only by the intended destination node. Bridges learn which addresses are on which network and develop a learning table so that subsequent messages can be forwarded to the right network. 5
Bridging networks are generally always interconnected local area networks since broadcasting every message to all possible destinations would flood a larger network with unnecessary traffic. For this reason, router networks such as the Internet use a scheme that assigns addresses to nodes so that a message or packet can be forwarded only in one general direction rather than forwarded in all directions. A bridge works at the data-link (physical network) level of a network, copying a data frame from one network to the next network along the communications path. A bridge is sometimes combined with a router in a product called a brouter.• Coaxial Cable: Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network. Coaxial cable is called "coaxial" because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry information for a great distance. Coaxial cable was invented in 1929 and first used commercially in 1941. AT&T established its first cross-continental coaxial transmission system in 1940. Depending on the carrier technology used and other factors, twisted pair copper wire and optical fiber are alternatives to coaxial cable.• Optical Fiber Cable:• Twisted Pairs Cable: • Ethernet Card: Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD ) protocol. 6
Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second. Ethernet was named by Robert Metcalfe, one of its developers, for the passive substance called "luminiferous (light-transmitting) ether" that was once thought to pervade the universe, carrying light throughout. Ethernet was so- named to describe the way that cabling, also a passive medium, could similarly carry data everywhere throughout the network.• Wireless LAN: A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection. High-bandwidth allocation for wireless will make possible a relatively low-cost wiring of classrooms in the United States. A similar frequency allocation has been made in Europe. Hospitals and businesses are also expected to install wireless LAN systems where existing LANs are not already in place.• Gateway: A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your companys network or at your local Internet service provider (ISP) are gateway nodes. In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.• HUB: Used as a Repeator, to emitate a Star network using a Bus network.• Modem: Enables to send and receive data through Telephone lines. 7
Data Transmission: Data are transmited as Packets.A packet is the unit of data that is routed between an origin and a destination on thenetwork. the file is divided into "chunks" of an efficient size for routing. Each ofthese packets is separately numbered and includes the Internet address of thedestination. The individual packets for a given file may travel different routes throughthe Internet. When they have all arrived, they are reassembled into the original file. Header File’s DATA Trailer A Packet (Chunk) of File’s DataPacket #, Sender & Reciver Address Actual Data checking equation Network 01001001101110100010 Network Card Communication Line CardParallel Transmission Serial Transmission Parallel Transmission Sender Computer Receiver Computer Lecture Prepared by: Assist. Prof. Emad Jihad 8