Lecture #25: Networks and Communications Communication and Networks What will we learn? How a communications system works What a network is What networks used for What network operating systems do What LAN, WAN and MAN are What a peer-to-peer network LAN is What a client/server LAN is Network topologies 1
Uses of Communications and Network Technology Voice mail: allows caller to leave a message by converting the analog signal into digital form. Fax: transmit or receive documents over telephone lines. E-mail: allows users to exchange text messages over a network. Chat rooms/ Instant messaging: real-time communications. Newsgroup: conversation about a particular topic (not real-time). Internet telephony: audio (voice) communications over a network. Videoconferencing: real-time audio and video communications. Communications Systems Consist of: Sending side: Sending device Communications device Communication channel Receiving side: Communications device Receiving device 2
Sending and Receiving Devices Initiate or accept transmission of data, instructions and information. s (notebook or desktop) Servers Mainframes Handheld devices Communications Channel 1: Sending device requests information 2: When request leaves the ISP, it travels over a variety of lines until it reaches Internet backbone 3: Request travels over T3 lines along Internet backbone 4: Request travels over T1 lines until it reaches destination network server destination network server T1 lines T3 lines T1 lines T1 lines 3
Communications devices Hardware that converts the data, instructions or information to digital signals. Also must be capable of transmitting and/or receiving data, instructions and information. Dial-up modems ISDN or DSL modems cable modems network interface cards Telephone networks Dial-up: temporary connection using analog phone line. Dedicated line: constant connection which can be either digital or analog ISDN/ DSL lines: digital lines provide faster transmission rates than analog. Cable TV lines: type of dedicated line allowing internet connection. T-carrier lines: allow multiple signals (fast transfer rates) 4
Networks collection of computers and devices connected together to allow users to: facilitate communications share hardware share data and information share software Network operating Systems Perform the following tasks: Administration (adding and deleting users) File management (locating and transferring files) Hardware management (like printers) Security 5
Uses and Types of Networks: LANs A network is created when data communication channels link more than one computer or device. These connections can be permanent or temporary. Networks allow communication over short and vast distances and also allow users to share data. There are two basic types: local area networks and wide area networks. Local Area Networks or LANs LANs link computers and users in a more defined area, such as an office, a Network building, or adjacent buildings. printer s in a LAN usually share one or more printers and storage devices. A LAN can be connected to another LAN by use of a bridge. A LAN can be connected to a dissimilar network type by using a gateway. A LAN can also be connected to a wide area network (WAN) by using a router. Network hard drives Local printer Types of LANs Peer-to-peer Client/Server clie nt clie nt clie nt laser printer serv er 6
Wide Area Networks or WANs Uses and Types of Networks: WANs WANs link computers and users over a wide geographic area. Wide area networks are usually linked by high-speed telephone communication channels or by satellite and microwave relays. A network in Los Angeles Modem Modem connection Modem A network in New York Printer Other network types: Client-Server Networks In a client-server network, one or more computers on the network function as file servers. These file servers store programs and data which are accessed by other computers on the network, called clients. Peer-to-Peer Networks In a peer-to-peer network every computer is both a client and a server. All computers on the network are able to access and provide data to all the computers. Uses and Types of Networks: MANs Metropolitan Area Networks or MANs 7
Network Layouts Local area networks can be organized in different ways. The three most common topologies of networks are linear bus, star, and ring. Linear Bus Networks In a linear bus network, a single path (bus) connects each node (computer). Using a transceiver on each node, data is allowed to be sent along the bus in both directions. Linear networks encounter problems when two or more nodes send data at the same time, which jams and blocks all transmissions. The network will go down if a node is broken from the connection. Printer Printer Bus Star Networks In a star network, each node is connected by its own path to the central hub. The hub acts as a switching station, routing data to the appropriate node. This topology prevents data jamming or collisions from occurring. This network can remain active even when a node is broken from the connection. Printer Host computer 8
Ring Networks This network connects each node to every other node in a circular path. Messages and data travel around the circular path until reaching the destination. Ring networks prevent data collisions. Ring networks will go down if a node connection is broken. Printer Token Ring LAN technology that controls access to network by requiring network devices to share or pass a special signal, called a token Device with token can transmit data over network Only one token exists per network Based on ring topology, although it can use star topology 9
Ethernet LAN technology that allows personal computers to contend for access to network personal compute r personal compute r personal compute r Based on bus technology personal compute r personal compute r TCP/IP transmission control protocol/internet protocol Transmits data by breaking it up into packets Commonly used for Internet transmissions packets - Data divided into small pieces called packets routers - Devices that direct packets along fastest available path packet switching - technique of breaking a message into packets, sending packets, and then reassembling data 10
What is the Wireless Applications Protocol (WAP)? Allows wireless mobile devices to access Internet and its services Wireless device contains client software,which connects to Internet service provider's server Internal Networks Intranet Internal network that us Internet technologies Lets company make information accessible to employees and facilitate working in groups Typically includes a connection to Internet Extranet Allows customers or suppliers to access part of company s intranet 11
Linking Networks to the Internet Network Network Modem Workstation Router Mainframe Internet Provider Satellite Link Router Network Access Point Network Access Point Router Network Network Regional Network Regional Network Twisted-pair cables Common medium for connecting computers. Consists of plastic-wrapped copper wires in a plastic casing. Used in telephone and specially designed twisted-pair networks. Potential bandwidth up to 6 Mbps. Good for Internet and modem data connections but impractical for real-time music and video. Limits bandwidths of telephone/modem connections because the digital signals must be translated to analog signals. Copper wires Plastic wrapping Plastic casing 12
Coaxial Cables Coaxial cables are often used for VCR, cable TV connections, telephone networks, and some computer networks. Coaxial cables consist of a center copper wire, insulation sheathing, a conducting and shielding wire mesh that protects against interference, and a plastic outer sheathing. Baseband and broadband coaxial cables are the two main types of coaxial cable. Baseband transmits one digital channel at 10 to 80 Mbps. Broadband transmits multiple analog channels. Baseband coaxial cable is used in computer networks. Broadband coaxial cable is used in cable television transmissions. Copper wire Plastic sheathing Insulation sheathing Wire mesh Fiber Optic Cables Fiber optic cable is a string of glass used to transmit light or photons. It contains a very pure central glass filament surrounded by a refractive material called cladding. Digital pulses at one end of the cable are translated into light pulses by use of a laser. The light pulses travel down the cable by bouncing off the cladding. The other end of the cable has a photodetector which transforms the light back into electrical impulses. Capable of transmitting up to 1000 billion bps. No interference from electromagnetic fields. Very expensive to install. Used primarily in telephone lines. 13
What you need to know How a communications system works What a network is What networks used for What network operating systems do What LAN, WAN and MAN are What a peer-to-peer network LAN is What a client/server LAN is Network topologies Reading Assignment: Chapter 10 in Discovering s 2003: E-Commerce and Society 14
Return to Lynne s website To return to Lynne Mayer s website, click on one of the following links: Lynne s homepage CIS110 CIS121 15