KINDS OF NETWORKSPeer-to-Peer NetworksIn a peer-to-peer network, there are no dedicated servers, and there isno hierarchy among the computers. All the computers are equal andtherefore are known as peers. Each computer functions as both a clientand a server.And there is no administrator responsible for the entire network. The userat each computer determines what data on that computer is shared onthe network. Below figure shows a peer-to-peer network in which eachcomputer functions as both a client and a server.Computers in a peer-to-peer network are called peers. In a peer-to-peernetwork, all computers are considered equal; they all have the sameabilities to use the resources available on the network. Each computer canfunction both as a client and a server. Computers are not dedicated tofunction as servers. They use the network to share resources among theindependent peers. The computer whose applications are required by theother networked computers functions as a server. The other computersfunction as clients. Therefore, a dedicated administrator is not assignedfor network management.A peer-to-peer network is a small group of people using a network. Peer-to-peer networks members usually perform similar tasks, whichnecessitates the sharing of resources. The peer-to-peer networks support10 computers. The users in a peer-to-peer network are located in thesame geographical area. Operating systems, such as Microsoft Windows98 or Microsoft Windows XP, can be used to set up a peer-to-peer
network. Additional software is not required because peer-to-peernetworking is built into the systems.Another important point of peer-to-peer networks is that the users ofeach computer plan and control the security of their resources. The usersdetermine the resources on their computers, which can be shared on thenetwork. The shared network resources, such as disk space, printers orfaxes, can be used by anyone who has access to the network. This ispossible only if the shared network resources are not password protected.Peer-to-peer networks have weak and intrusive security because a centralserver is not used to administer and secure the network. In addition,some users may not implement security.A peer-to-peer network does not support a central login process. Thisimplies that a user who logs on to one peer can access any sharednetwork resource, which is not controlled by a specific password. Peer-to-peer networks are relatively simple. Because each computer functions asa client and a server, there is no need for a powerful central server or forthe other components required for a high-capacity network. Peer-to-peernetworks can be less expensive than server-based networks.Peer-to-peer networks are simple and inexpensive to install and maintain.The cost of implementing peer-to-peer networks is low because a centralserver is not used to administer the network. In addition, the componentsfor a high-capacity network are not required in a peer-to-peer network.In a peer-to-peer network, the users handle administration. This meansthat all the users need to be trained in how to share files, folders, andprinters. In a peer-to-peer network, suddenly shutting down yourcomputer can cause one of your colleagues to be unable to print.Peer-to-peer networks are appropriate for environments where all theusers are located in the same geographical area and the network securityis not an important factor. In addition, these networks are useful whenthe network expansion is limited.Advantages of a peer-to-peer network: Less initial expense - No need for a dedicated server. Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations.Disadvantages of a peer-to-peer network: Decentralized - No Centralized server. Security - Does not provide the security available on a peer-to-peer network.
Server Based NetworksA dedicated server is one that functions only as a server and is not usedas a client or workstation. Server based networks (see below Figure) havebecome the standard models for networking.In a server-based network, clients rely on the services that the serverprovides, such as file storing and printing. Client computers are generallyless powerful than server computers.A server-based network using network operating system is that thenetworks are organized into domains. A domain is a collection of networksand clients that share security information. Domain security and logonpermissions are controlled by special servers called domain controllers.Users cannot access the resources of servers in a domain until a domaincontroller has authenticated them.In server-based networks, a network administrator centrally manages theresource security. The administrator defines and manages user access tonetwork resources.Another beneficial of server-based networks is central file storage.Server-based networks provide easy backup of critical data. Data backupis another useful characteristic of server based networks.Server based networks can support a larger number of users than peer-to-peer networks. To support a large number of users, server-basednetworks use monitoring and network management tools. Servers mustperform varied and complex tasks. (See below figure)
Security is often the primary reason for choosing a server-based approachto networking. In a server-based environment, one administrator whosets the policy and applies it to every user on the network can managesecurity. (see below figure)Advantages of a client/server network Centralized - Resources and data security are controlled through the server. Security - More security then Peer-to-peer network. Flexibility - New technology can be easily integrated into system. Interoperability - All components (client /server) work together. Accessibility - Server can be accessed remotely and across multiple platforms.
Disadvantages of a client/server network Expense - Requires initial investment in dedicated server. Maintenance - Large networks will require a staff to ensure efficient operation. Dependence - When server goes down, operations will cease across the network.A LAN is a network with two or more computers connected to each other in a single locationWired Local Area Network (LAN)It is the simplest type of network in which computers are connected toeach other by cables.Each of the computers on the LAN is also called a node .A LAN is characterized by three primary attributes: TopologyThe topology is the pattern used to connect the computers together. Witha bus topology, a network cable connects each computer to the next one,forming a chain. With a star topology, each of the computers is connectedto a central nexus called a hub/Switch. A ring topology is essentially a busnetwork with the two ends joined together. (You will see more aboutnetwork topologies in Chapter 6) Medium
Four basic types of media are used in local-area networks; coaxial cable,twisted-pair wires, fiber-optic cable, And wireless.Each medium has its advantages and disadvantages relative to cost,speed, and expandability. Coaxial cables provide high speed and low errorrates. Twisted-pair wires are cheaper than coaxial cables, can sustain thespeeds common to most personal computers, and are easy to install.Fiber-optic cable is the medium of choice for high-speed local-areanetworks. Wireless local-area networks have the advantage ofexpandability. (You will see more about network medium in Chapter 5.2) ProtocolsThe topology and the medium used on a particular network are specifiedby the protocol. (You will see more about protocol in Chapter 8).LAN computer networks that usually cover a limited range, say, within theboundary of a building. A LAN computer network is two or morecomputers that communicate with each other through some medium.The primary usage of local-area networks (LANs) is the sharing ofhardware, software, or information, such as data files, multimedia files, orelectronic mail. Resource sharing provided by local-area networksimproves efficiency and reduces overhead.There are a number of ways in which nodes can communicate over anetwork. The simplest is to establish a dedicated link between thetransmitting and receiving stations. This technique is known as circuitswitching. A better way of communicating is to use a technique known aspacket switching, in which a dedicated path is not reserved between thesource and the destination. Data are wrapped up in a packet andlaunched into the network. In this way, a node only has exclusive accessto the medium while it is sending a packet. During its inactive period,other nodes can transmit. A typical packet is divided into preamble,address, control, data, and error-check fields.The computers in a LAN are connected by using cables. This methodcannot be used to connect computers that are in different locations, forexample, in buildings across a town or city. Therefore, a LAN is notsuitable for large businesses with offices in several locations.Wireless Local Area NetworkThe term wireless networking refers to technology that enables two ormore computers to communicate using standard network protocols, butwithout network cabling.
Peer-to-peer wireless network consists of a number of computers eachequipped with a wireless networking interface card. Each computer cancommunicate directly with all of the other wireless enabled computers.They can share files and printers this way, but may not be able to accesswired LAN resources, unless one of the computers acts as a bridge to thewired LAN using special software.A wireless network can also use an access point, or base station. In thistype of network the access point acts like a hub, providing connectivity forthe wireless computers. It can connect the wireless LAN to a wired LAN,allowing wireless computer access to LAN resources, such as file serversor existing Internet Connectivity.There are two types of access points: Hardware access points (HAP)Hardware access points offer complete support of most wireless features,but check your requirements carefully. Software Access Points
Software Access Points which run on a computer equipped with a wirelessnetwork interface card as used in peer-to-peer wireless network. Thesoftware routers that can be used as a basic Software Access Point, andinclude features not commonly found in hardware solutions.Connected wireless LAN to wired LANTo do this you will need some sort of bridge between the wireless andwired network. This can be accomplished either with a hardware accesspoint or a software access point.Hardware access points are available with various types of networkinterfaces, such as Ethernet or Token Ring, but typically require extrahardware to be purchased if youre networking requirements change. Ifnetworking requirements go beyond just interconnecting a wired networkto a small wireless network, a software access point may be the bestsolution.A software access point does not limit the type or number of networkinterfaces you use. It may also allow considerable flexibility in providingaccess to different network types, such as different types of Ethernet,Wireless and Token Ring networks. Such connections are only limited bythe number of slots or interfaces in the computer used for this task.Further to this the software access point may include significant additionalfeatures such as shared Internet access, web caching or content filtering,providing significant benefits to users and administrators.Wireless networking offers a cost-effective solution to users with difficultphysical installations such as campuses, hospitals or businesses withmore than one location in immediate proximity but separated by publicthoroughfare.This type of installation requires two access points. Each access point actsas a bridge or router connecting its own LAN to the wireless connection.
The wireless connection allows the two access points to communicate witheach other, and therefore interconnect the two LANs.Wireless network rangeEach access point has a finite range within which a wireless connectioncan be maintained between the client computer and the access point. Theactual distance varies depending upon the environment; manufacturerstypically state both indoor and outdoor ranges to give a reasonableindication of reliable performance. Also it should be noted that whenoperating at the limits of range the performance may drop, as the qualityof connection deteriorates and the system compensates.Typical indoor ranges are 150-300 feet, but can be shorter if the buildingconstruction interferes with radio transmissions. Longer ranges arepossible, but performance will degrade with distance. Outdoor ranges arequoted up to 1000 feet, but again this depends upon the environment.There are ways to extend the basic operating range of Wirelesscommunications, by using more than a single access point or using awireless relay /extension point. Multiple access points can be connected toa wired LAN, or sometimes even to a second wireless LAN if the accesspoint supports this.In most cases, separate access points are interconnected via a wired LAN,providing wireless connectivity in specific areas such as offices or rooms,but connected to a main wired LAN for access to network resources, suchas file servers.
If a single area is too large to be covered by a single access point, thenmultiple access points or extension points can be used. Note that an"extension point" is not defined in the wireless standard, but have beendeveloped by some manufacturers.When using multiple access points, each access point wireless area shouldoverlap its neighbors. This provides a seamless area for users to movearound in using a feature called "roaming.” See Roaming for furtherinformation.Some manufacturers produce extension points, which act as wirelessrelays, extending the range of a single access point. Multiple extensionpoints can be strung together to provide wireless access to far awaylocations from the central access point.
RoamingA wireless computer can "roam" from one access point to another, withthe software and hardware maintaining a steady network connection bymonitoring the signal strength from in-range access points and locking onto the one with the best quality.Usually this is completely transparent to the user; they are not aware thata different access point is being used from area to area. Some accesspoint configurations require security authentication when swapping accesspoints, usually in the form of a password dialog box.Access points are required to have overlapping wireless areas to achievethis as can be seen in the following diagram.
A user can move from Area 1 to Area 2 transparently. The Wirelessnetworking hardware automatically swaps to the Access Point with thebest signal.Sharing an internet connection in wireless networkTo share an Internet connection across a LAN you need two things: an Internet sharing hardware device or software program a LANIf your LAN is wireless. You need hardware or software access point and awireless LAN. Any computer equipped with a wireless network cardrunning suitable Internet sharing software can be used as a softwareaccess point. A number of vendors offer hardware access points.A hardware access point may provide Internet Sharing capabilities toWired LAN computers, but does not usually provide much flexibilitybeyond very simple configurations.If an existing wired LAN already has an Internet connection, then thehardware access points simply connect to LAN and allow wirelesscomputers to access the existing Internet connection in the same way aswired LAN computers.
Wireless Network securityWireless communications obviously provide potential security issues, asan intruder does not need physical access to the traditional wired networkin order to gain access to data communications. However, 802.11 wirelesscommunications cannot be received much less decoded by simplescanners, short wave receivers etc. This has led to the commonmisconception that wireless communications cannot be eavesdropped atall. However, eavesdropping is possible using specialist equipment.To protect against any potential security issues, 802.11 wirelesscommunications have a function called WEP (Wired Equivalent Privacy), aform of encryption which provides privacy comparable to that of atraditional wired network. If the wireless network has information thatshould be secure then WEP should be used, ensuring the data is protectedat traditional wired network levels.IEEE 802.11Wireless networking hardware requires the use of underlying technologythat deals with radio frequencies as well as data transmission. The mostwidely used standard is 802.11 produced by the Institute of Electrical andElectronic Engineers (IEEE). This is a standard defining all aspects ofRadio Frequency Wireless networking.Also it should be noted that traditional Virtual Private Networking (VPN)techniques will work over wireless networks in the same way astraditional wired networks.
Wide Area Network (WAN)A wide area network (WAN) is a telecommunications network, usuallyused for connecting computers, that spans a wide geographical area.WANs can by used to connect cities, states, or even countries.An example of a WAN connection would be a company with two offices indistant cities, each with its own LAN and connected by a leased telephoneline. This type of WAN is illustrated in below figure. Each end of theleased line is connected to a router and the routers are connected toindividual LANs. Any computer on either of the LANs can communicatewith any one of the other computers at the other end of the WAN link orwith a computer on its own LAN.WANs are often used by larger corporations or organizations to facilitatethe exchange of data and in a wide variety of industries, corporations withfacilities at multiple locations have embraced WANs. Increasingly,however, even small businesses are utilizing WANs as a way of increasingtheir communications capabilities.Although WANs serve a purpose similar to that of local area networks(LANs), WANs are structured and operated quite differently. The user of aWAN usually does not own the communications lines that connect theremote computer systems; instead, the user subscribes to a servicethrough a telecommunications provider. Unlike LANs, WANs typically donot link individual computers, but rather are used to link LANs. WANs alsotransmit data at slower speeds than LANs.WANs have existed for decades, but new technologies, services, andapplications have developed over the years to dramatically increase theirefficacy for business. WANs were originally developed for digital leased-line services carrying only voice, rather than data. As such, they
connected the private branch exchanges (PBXs) of remote offices of thesame company. WANs are still used for voice services, but today they areused more frequently for data and image transmission (such as videoconferencing). These added applications have spurred significant growthin WAN usage, primarily because of the surge in LAN connections to thewider networks.WANs are either point-to-point, involving a direct connection between twosites, or operate across packet-switched networks, in which data istransmitted in packets over shared circuits. Point-to-point WAN servicemay involve either analog dial-up lines, in which a modem is used toconnect the computer to the telephone line, or dedicated leased digitaltelephone lines, also known as "private lines." Analog lines, which may beeither part of a public-switched telephone network or leased lines, aresuitable for batch data transmissions, such as congruent order entry andpoint-of-sale transactions. Dedicated digital phone lines permituninterrupted, secure data transmission at fixed costs.Point-to-point WAN service providers include both local telephonecompanies and long distance carriers. Packet-switched network servicesare typically chosen by organizations which have low volumes of data ornumerous sites, for which multiple dedicated lines would be tooexpensive.Depending on the service, WANs can be used for almost any data sharingpurpose for which LANs can be used. Slower transmission speeds,however, may make some applications less practical for WANs. The mostbasic uses of WANs are for electronic mail and file transfer, but WANs canalso permit users at remote sites to access and enter data on a centralsites database, such as instantaneously updating accounting records.New types of network-based software that facilitate productivity andproduction tracking, such as groupware and work-flow automationsoftware, can also be used over WANs. Using groupware, workers atdispersed locations can more easily collaborate on projects. WANs alsogive remote offices access to a central offices other data communicationsservices, including the Internet.Wireless Fidelity Wi-Fi
A typical Wi-Fi setup contains one or more Access Points (APs) and one ormore clients. An AP broadcasts its SSID (Service Set Identifier, "Networkname") via packets that are called beacons, which are usually broadcastevery 100 ms. The beacons are transmitted at 1 Mbit/s, and are ofrelatively short duration and therefore do not have a significant effect onperformance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that theclient who receives the beacon can communicate at least 1 Mbit/s. Basedon the settings (e.g. the SSID), the client may decide whether to connectto an AP. If two APs of the same SSID are in range of the client, the clientfirmware might use signal strength to decide which of the two APs tomake a connection to.The Wi-Fi standard leaves connection criteria and roaming totally open tothe client. This is a strength of Wi-Fi, but also means that one wirelessadapter may perform substantially better than the other. Since Wi-Fitransmits in the air, it has the same properties as a non-switchedethernet network.Wi-Fi DevicesWireless Access Point (WAP)A wireless access point (AP) connects a group of wireless stations to anadjacent wired local area network (LAN). An access point is similar to anethernet hub or switch, but instead of relaying LAN data only to other LANstations, an access point can relay wireless data to all other compatiblewireless devices as well as to a single (usually) connected LAN device, inmost cases an ethernet hub or switch, allowing wireless devices tocommunicate with any other device on the LAN.Wireless RoutersA wireless router integrates a wireless access point with an IP router andan ethernetswitch . The integrated switch connects the integrated accesspoint and the integrated ethernet router internally, and allows for externalwired ethernet LAN devices to be connected as well as a (usually) singleWAN device such as cable modem or DSL modem . A wireless routeradvantageously allows all three devices (mainly the access point androuter) to be configured through one central configuration utility, usuallythrough an integrated web server .Wireless Ethernet BridgeA wireless Ethernet bridge connects a wired network to a wirelessnetwork. This is different from an access point in the sense that an accesspoint connects wireless devices to a wired network at the data-link layer .Two wireless bridges may be used to connect two wired networks over a
wireless link, useful in situations where a wired connection may beunavailable, such as between two separate homes.Advantages of Wi-Fi Allows LANs to be deployed without cabling, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs. Wi-Fi silicon pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever- widening array of devices. Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are interoperable and include WPA2 security. Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area. Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area. Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.Disadvantages of Wi-Fi Wi-Fi can be interrupted by other devices, notably 2.4 GHz cordless phones and microwave ovens. Power consumption is fairly high compared to some other standards, making battery life and heat a concern. The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be breakable even when correctly configured. Wi-Fi Access Points typically default to an open ( encryption -free) mode. Novice users benefit from a zero configuration device that works out of the box but might not intend to provide open wireless access to their LAN. Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g with a stock antenna might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band, as Wi-Fi is no exception to the physics of radio wave propagation. Wi-Fi in the 2.4 GHz frequency block has better range than Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi
(and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennascan be several kilometres or more with line-of-sight.Wi-Fi networks can be monitored and used to read and copy data(including personal information) transmitted over the network when noencryption such as VPN is used.