WHAT IS A NETWORK? A network is simply two or more computersthat are linked together. The most common types of networks are:Local Area Networks (LANS) and Wide Area Networks (WANS). The primary difference between the two isthat a LAN is generally confined to a limitedgeographical area, whereas a WAN covers alarge geographical area. Most WANs aremade up of several connected LANs.
TYPES OF NETWORKS Local Area Network (LAN) – a network that spans asmall area such as a building or an office. Software applications and other resources are stored on afile server. Print servers enable multiple users to share the sameprinter. Wide Area Network (WAN) – a network that spans awide geographical area; there are several types ofWANS Metropolitan area network (MAN) Public access network (PAN) Value added network (VAN) Virtual private network (VPN)
TYPES OF NETWORKS Intranet – An intranet is a private LAN designed foruse by everyone within an organization. An intranetmight consist of an internal e-mail system, a messageboard and one or more Web site portals that containcompany news, forms, and personnel information.Access to an intranet’s web site is restricted by afirewall. Extranet – a network that connects people withinyour company with people who are outside yourcompany--all within a secure, password-protectednetwork that can be accessed from anywhere.http://www.clienthelpdesk.com/dictionary
BENEFITS OF ANETWORK Information sharing: Authorized users can use othercomputers on the network to access and share information and data.This could include special group projects, databases, etc. Hardware sharing: One device connected to a network, suchas a printer or scanner, can be shared by many users. Software sharing: Instead of purchasing and installing asoftware program on each computer, it can be installed on the server.All of the users can then access the program from a single location. Collaborative environment: Users can work together ongroup projects by combining the power and capabilities of diverseequipment.Ambrose, Bergerud, Busche, Morrison, and Wells-Pusins: IC3 BASICS, Thomson Course Technology, 2003
RISKS OF NETWORKCOMPUTING The security of a computer network ischallenged everyday by: Equipment malfunctions System failures Note: equipment malfunctions and system failures maybe caused by natural disasters such as floods, storms, orfires, and electrical disturbances Computer hackers Virus attacksAmbrose, Bergerud, Busche, Morrison, and Wells-Pusins: IC3 BASICS, Thomson Course Technology, 2003
COMMUNICATIONSMEDIA Communications Channel To transfer data from one computer to anotherrequires some type of link through which the datacan be transmitted. This link is known as thecommunications channel. To send data through the channel requires sometype of transmission media, which may be eitherphysical or wireless.
PHYSICAL MEDIA Twisted-pair cable – consists of two independentlyinsulated wires twisted around each other (leastexpensive type of cable—the kind that is used in many telephonesystems) Coaxial cable – consists of an insulated center wiregrounded by a shield of braided wire (the primary type ofcabling used by the cable television industry; it is more expensive thantwisted pair) Fiber-optic cable – contains hundreds of clearfiberglass or plastic fibers (threads) (made from thin, flexibleglass tubing; bandwidth is greater, so it can carry more data; it is lighterthan metal wires and is less susceptible to interference; it is fragile andexpensive) ISDN line – a special digital telephone line thattransmits and receives information at very highspeedsFuller, Floyd, Computers: Understanding Technology: EMC Paradigm, 2003.
WIRELESS MEDIA Microwave system – transmits data via high-frequency radio signals through the atmosphere Satellite system – receive transmitted signals, amplifythem, and then transmit the signals to the appropriatelocations Cellular technology – uses antennae resemblingtelephone towers to pick up radio signals within aspecific area (cell) Infrared technology – transmits data as infrared lightwaves from one device to another, providing wirelesslinks between PCs and peripheralsNote: The type selected is determined by the type ofnetwork, the size of the network, and the cost.Fuller, Floyd, Computers: Understanding Technology: EMC Paradigm, 2003.
HOW ARE NETWORKSCATEGORIZED? Networks are usually classified usingthree properties:TopologyProtocolArchitecture
NETWORKTOPOLOGIES Network Topology (or layout) – refers to the waycomputers and peripherals are configured to formnetworks Bus topology – all computers are linked by a singleline of cable Star topology – multiple computers and peripheraldevices are linked to a central computer, called ahost Ring topology – each computer or workstation isconnected to two other computers, with the entirenetwork forming a circle Hybrid topology – combine network layouttypes to meet their needs
NETWORK/COMMUNICATIONPROTOCOLS A protocol is simply an agreed-on set ofrules and procedures for transmitting databetween two or more devices. Features determined by the protocol are: How the sending device indicates it has finishedsending the message. How the receiving device indicates it has receivedthe message. The type of error checking to be used.Ambrose, Bergerud, Busche, Morrison, and Wells-Pusins: IC3 BASICS, Thomson Course Technology, 2003
NETWORK/COMMUNICATIONSPROTOCOLS Most networks use Ethernet, but somenetwork may use IBM’s Token Ringprotocol. On the Internet, the major protocol isTCP/IP (an acronym for TransmissionControl Protocol/Internet Protocol).Networks for Beginners: http://compnetworking.about.com/
EXAMPLE OF AN ETHERNETBUS Ethernet LANs use a bustopology. All stations are connected toa single long cable. Any station can send asignal along the cable, whichall other stations will receive.Unlike ring topologies, thecable doesnt close a loop.Networks for Beginners: http://compnetworking.about.com/
TOKEN RING NETWORK A token passing ring LAN is agroup of computers connected ina loop. The group uses a tokenpassing access mechanism. A computer wishing to send datashould first receive permission.When it gets control of thenetwork it may transmit a frame.Each frame transmitted on thering is transmitted from onecomputer to the next, until itultimately returns to the initiator ofthe transmission.Networks for Beginners: http://compnetworking.about.com/
INTERNET PROTOCOLSNetworks for Beginners: http://compnetworking.about.com/
NETWORKING HARDWAREAND SOFTWARE Hub – electronic device (with a number of ports) usedin a LAN to link groups of computers Repeaters (also called amplifiers) – electronic devicesthat receive signals and amplify and send them alongthe network Routers - electronic devices used to ensuremessages are sent to their intended destinations Gateway – consists of hardware and/or software thatallows communications between dissimilar networks Bridge – consists of hardware and/or softwarethat allows communication between twosimilar networks
HUBSThe original Ethernet LANs relied on certain physicalcharacteristics of the cable carrying the network data(usually coaxial cable). New Ethernet technologiesintroduced new cable types that we unable to fulfill theoriginal physical requirements. New devices - hubs -were introduced to simulate those characteristics.Simply put, the hubs major function is to replicate data itreceives from one device attached to it to all others.Networks for Beginners: http://compnetworking.about.com/
REPEATERSAn illustration of a repeater at workThe electrical signal entering the repeater at one end is weakened.The repeater amplifies the electrical signals and resends the data.A common problem in the networking world is that of weakeningelectrical signals. Electrical signals traveling through wires (such ascopper wires used in most networks), weaken due to the wireselectrical resistance. This effect limits the lengths of the cable that canbe used. A repeater will overcome this limit, when there is a need toconnect two computers at a larger distance.A repeater is connected to two cable segments. Any electrical signalreaching the repeater from one segment, will be amplified andretransmitted to the other segment.Networks for Beginners: http://compnetworking.about.com/
ROUTERS Routers connect two or more networks and forward datapackets between them. When data arrives from one ofthe segments, the router decides, according to its routingtable, to which segment to forward that data.Networks for Beginners: http://compnetworking.about.com/
GATEWAY "Gateway" is a term that was once used to refer to a routing device.Today, in the TCP/IP world, the term "router" is used to describe such adevice.The term gateway now refers to special-purpose devices, that performprotocol conversions. Gateways implement application layerconversions of information received from various protocols. Examples of gateways found on todays markets are: VocalTec Gateway: A gateway that converts human speech traveling onanalog phone lines into local area network protocol data, and visa-versa. RadVision Gateway: Converts video from digital phone lines into local areanetwork protocol data, and visa-versa.Networks for Beginners: http://compnetworking.about.com/
MODEMSAn illustration of data sent using a modem and a regulartelephone line.A modem is a device that converts digital data originating from aterminal or computer, to analog signals used by voicecommunication networks such as the telephone system. At oneend, modems convert the digital pulses to audible tones andconvert audio tones back to digital pulses at the other.The word "Modem" stands for "MOdulator-DEModulator".Networks for Beginners: http://compnetworking.about.com/
MODEMS Transmission speedModems are available in different transmission speeds, whichare measured in BPS (bits per second) also called BAUD rate.Standard modems speeds: 9600 baud, 14400 baud, 28800baud, 33600 baud, 56800 baud. Internal/ExternalInternal modems are electronic cards. An internal modem isinstalled in one of the computers expansion slot.External modems are fully functioning external devices. Theexternal modem is connected to a computer using a serialcable to one of the computers serial ports, and draws powerfrom an external power source.Networks for Beginners: http://compnetworking.about.com/
EXAMPLE OFFIREWALL Firewalls are systems that establish access control policiesamong networks. They can block information from enteringa network or from getting out of that network, they canpermit different users to perform different kinds ofoperations, according to the users authorizations.Networks for Beginners: http://compnetworking.about.com/
NETWORKARCHITECTURE Network architecture – refers to the way anetwork is designed and built. The two majortypes are: Peer-to-peer architecture – Computers connectwith each other in a workgroup to share files,printers, and Internet access. This is used toconnect a small number of computers. Client/server architecture – sends information froma client computer to a server, which then relays theinformation back to the client computer, or to othercomputers on the networkNetworks for Beginners: http://compnetworking.about.com/
COMMUNICATIONPROTOCOLS File transfer protocol (FTP) – used to transmit files. Simple mail transfer protocol (SMTP) – used totransmit e-mail messages. Post office protocol (POP) – allows the recipient toretrieve messages. Wireless application protocol – enables wirelessdevices to access and use the Internet using aclient/server network. 802.11 – protocol for wireless LAN technology
DATA TRANSMISSIONCHARACTERISTICS Bandwidth (rate of transmission) Analog or Digital (type of signal) Analog transmission – takes the form ofcontinuous waves transmitted over a medium at acertain frequency rage Digital transmission – sends data in the form of bits Serial or Parallel (order of bits) Serial transmission – all of the data bits aretransmitted one bit after another in a continuousline Parallel transmission – data bits are sent at thesame time along multiple paths
COMMUNICATIONSSOFTWARE E-Mail Software – used to send and receiveelectronic messages using the Internet Web Browser – allows users to access andview Web pages Groupware – allows groups of people on anetwork to share information and tocollaborate on various projects