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Transcript
Networks and the Internet Unit E 1 Objectives Introduce Networks Classify Networks Understand Network Topology Explore Network Hardware Explore Communications Channels Transport Data Explore LAN Standards Explore Wireless 2 Objectives Understand Internet connections Introduce IP Addresses and Domain Names Connect to the Internet using Dial-up Connect to the Internet using Broadband Connect to the Internet using Cable Connect to the Internet without Wires 3 Communications Network The combination of hardware, software and connecting links that transport data Data is encoded, sent to its destination then decoded Noise Encoded Data Source Signal Communications Channel Transmitter Decoded Data 4 Receiver Destination Shared Resources Networks share hardware, software, and data Sharing reduces costs – Peripheral devices, site licenses Provides access to Internet Share data – Groupware, e-mail, IM, online conferencing 5 Shared Resources (cont.) Networks are vulnerable – Unauthorized access – Malicious code • Viruses, Trojan horses, worms Networks are becoming more standardized Most benefits outweigh risks – Computers can be protected 6 Network Classifications by Geographic Coverage PAN: Personal Area Network (PDAs) WAN: Wide Area Network (Internet is one) MAN: Metropolitan Area Network (50 miles) LAN: Local Area Network (single building) 7 Network Classifications by Organizational Structure Client/Server: – One or more computers configured as servers and other computers configures as clients – Server is central repository for data Peer-to-Peer (P2): – Treats every computer as an equal – Workstations transfer data to each other without going through server – File-sharing networks 8 Network Classifications by Organizational Structure 9 Network Software Licenses Single-user Multiple-user – Priced per user Concurrent-user – Certain number of copies at a time Site – Any and all computers at a location 10 Network Classifications CATEGORY DESCRIPTION EXAMPLES Geographical Area where network devices PAN, LAN, WAN, MAN are located Organizational Hierarchy of devices Client/Server, P2P Physical Layout and relationship between devices Star, bus, ring, mesh, tree Network Technologies for cables and signals that carry data Twisted-pair, coaxial, or fiber-optic cable; RF; microwaves; Infrared; power or phone line Bandwidth Capacity of network Broadband, narrowband Communications protocols Standards for orderly & safe data transfer TCP/IP, SPX/IPX, NetBEUI/NetBIOS, 11 AppleTalk Network Topology Physical arrangement of devices, cables, and wires 5 common topologies named for their shapes – Star (central connection point) – Ring (connects devices in a circle) – Bus (common backbone) – Mesh (each device connected to others) – Tree (blend of star and bus) 12 Network Topology Star Bus Ring 13 Network Topology (cont.) Each connection point on a network is a Node: – Server – Workstation – Network peripheral – Network device 14 Interconnecting Networks Two similar networks can be connected by a bridge – Transfers data without regard to format Gateway – A device or software used to join dissimilar networks by making data compatible Router – Electronic device that connects 2 or more networks 15 Network Hardware Overview 16 Network Hardware Server (also called host computer) – Distribute resources to network users – Contains network management software and files Workstation (also called client) – PC on a LAN – Client is software that lets it talk to server 17 Network Hardware Network Interface Card (NIC) – Example: Ethernet card Connection Devices – Modem: converts PC digital signals – Hub: connects nodes on a LAN – Router: decides best way to route data on network – Gateway: entrance to another network – Repeater: amplifies and regenerates 18 signals Network Addresses Physical address: – Every node has one – Built into circuitry of network device Logical address: – Used if physical address is incompatible with particular network 19 Wired Communication Channels Twisted-pair cables (phones) – STP: shielded twisted pair – UTP: unshielded twisted pair for small networks 20 Wired Communication Channels Coaxial cable (television) – High capacity 21 Wired Communication Channels Fiber-optic cable – Pulses of light in thin glass tubes – Essential to Internet backbone 22 Wireless Communication Channels RF: radio frequency signals – Send and receive by a transceiver with antenna Microwaves – More capacity than radio waves – Need clear path between transmitter and receiver – Cannot penetrate metal objects 23 Wireless Communication Channels Satellites – Signal relayed from ground station to satellite – Transponder on satellite receives, amplifies and retransmits signal back to earth – Key technology for Internet backbone 24 Wireless Communication Channels Infrared light – Short distance with clear line of site – Example: connect notebook with printer Laser light – Larger distance with clear line of site – Example: between buildings in future 25 Bandwidths The transmission capacity of a communications channel measured in bps (bits per second) Low-bandwidth carries less data than high bandwidth – Telephone – Narrowband High-bandwidth – Coaxial cable – DSL lines – Called broadband 26 Transporting Data Depends On: Network Topology: configuration Packet Switching Technology: determines how data is broken up Protocols: rules for successful and accurate data transmission 27 Packet Switching Technology Packet is a parcel of data on network or a file broken into small, equal size pieces Contains – – – – Sender address Destination address Sequence number Data Packet switching: packets sent independently of each other 28 Circuit Switching Establishes a dedicated, private link between phone lines during a call Inefficient because it reserves a circuit even if data is not being transmitted 29 Communications Protocol Allows two devices to negotiate and agree on how data will be transmitted TCP/IP – Transport Control Protocol/Internet Protocol – Most common – TCP: breaks data into packets – IP: addresses packets 30 Controlling Direction of Data Flow Simplex: one direction (TV) Half duplex: can send and receive data, but not at same time (CB radio) Full Duplex: can send and receive data at same time on same channel (Telephone) 31 Protocol Characteristics Handshaking: negotiating transmission speed Synchronous Protocol: sender and receiver synchronize signal with a fixed clock rate Asynchronous Protocol: requires a start and stop bit (most common) Parity bits: used for error checking 32 Communications Protocols PROTOCOL MAIN USE TCP/IP Internet NetBIOS/NETBEUI Microsoft networks Macintosh networks Novell networks AppleTalk IPX/SPX 33 LAN Standards Institute of Electrical and Electronics Engineers (IEEE) IEEE designation numbers identify compatible network technologies – ARCnet: old, simple, inexpensive – Token Ring: ring topology – FDDI: fiber-optic cables – Ethernet: simultaneous broadcast of data packets 34 Ethernet Packets accepted only by device to which it is addressed CSMA/CD protocol Refers to a family of LAN technologies – Various transmission rates – Fiber-optic and twisted-pair cables – Bus or star topology Connect many workstations 35 Ethernet 36 Home Ethernet Equipment Ethernet card in each workstation and peripheral device Link between network nodes such as cable Central connection point (hub) 37 Wireless Standards Wi-Fi (Wireless Fidelity) – Set of wireless networking technologies – Defined by IEEE 802.11 standards – Compatible with Ethernet Popular because of absence of cables Desirable for notebook and tablet computers 38 Wi-Fi Disadvantages Speed – Radio waves Distance – 25-150 feet Security – War driving/LAN-jacking – Wired Equivalent Privacy: encryption 39 Wi-Fi (cont.) Wi-Fi cards required – Include transceiver and antenna – Can be added to notebooks, PCs, and Tablets – Wireless access point is same as hub or router in Ethernet Bluetooth makes short-range wireless connections between devices such as a mouse, keyboard, printer 40 Internet Connections The Internet isn’t owned or operated by corporations or governments Traffic exceeds 100 trillion bytes (terabytes) each week Backbone provides high-speed routes for data traffic 41 Internet Connections Users connect to Internet Service Provider (ISP) or through LAN ISP provides e-mail and access to Web Networks use TCP/IP as standard 42 Internet Connections Ping software: Packet Internet Groper – Checks internet pathways to be sure they are open Traceroute software: traces data paths SMTP POP FTP SSL HTTP TELNET IMAP 43 IP Addresses ISP gives unique IP address to subscriber Series of numbers in 4 parts – 204.127.129.001 Static IP address: permanent, usually servers Dynamic IP address: temporary, for one session Look at your Internet configuration settings to find your IP address 44 Domain Names Translates directly into IP address Examples: course.com, rutgers.edu Top-level domain: indicated by extension ICANN handles domain name registration and control edu com info gov org mil int net 45 Dial-up Internet Connections Plain old telephone service (POTS) Dial-up connection via modem Circuit switching technology gives continuous private link 46 Dial-up Internet Connections Modem: Modulate/demodulate; digital to analog – Speed: 56 Kbps – Upstream actually 33 Kbps – Downstream actually 44 Kbps VIOP (Voice Over IP): can talk on computer at same time as running other programs on-line 47 Broadband Internet Connections High-speed digital communications links for voice and data DSL: Digital Subscriber Line (always-on) – Uses standard copper phone cables – Fastest and most affordable to individuals – Variations are ADSL, SDSL, HDSL AND DSL lite – DSL modems give 1.5 Mbps downstream 48 Broadband Internet Connections ISDN: Integrated Services Digital Network – 64 or 128 Kbps – Mostly used for business LANs – Need ISDN terminal adapter –1.544 Mbps –24 channels –43 Mbps T1 –Used by business and ISPs on dedicated leased lines –672 channels T3 –Also called DS3 (Digital Service-3) 49 Security When Always-On Same IP address when on – hackers can use High-speed access desirable for hackers Turn machine off often 50 Cable Internet Connections You need – Ethernet card – Cable modem: usual ISP provides – Splitter to connect both modem and TB if necessary Could slow down as more neighbors use service 51 Cable Security DOCSIS-compliant cable modems – Security technology filters packets to certain ports – Secures your computer from your neighbors – Doesn’t close up all security holes associated with always-on connections 52 Wireless Internet Connections DSS: Direct Satellite Service – Some allow only downstreaming Two-way Satellite Service – Downstream 500 Kbps vs. 40-60 Kbps upstream Cellular telephone infrastructure is slowest at 14.4 Kbps 53 Wireless Internet Connections Mobile Internet Connections Public Wi-Fi – Range of coverage: hotspot WWAN (wireless WAN) – Cell phone networks – Cell-ready modem or subscription WAP (wireless access protocol) 54 TechTalk: Installing a LAN Install Ethernet NIC – On motherboard or with PC card; both have port for network cable Attach cable to NIC port and hub port Turn on PCs Windows should automatically detect and establish connection Can activate file sharing and drive mapping by using Windows Network Neighborhood 55 Context: Education CBT (computer-based training) CAL (computer-aided learning) CAI (computer-aided instruction) Simulations 99% of American public schools have computers – Not all students have daily access though 56 Context: Education Some colleges require incoming students to have a computer DE/DL (Distance Education/Learning) Life-long learning 57 Issue: Free Wi-Fi? 58 Networks and the Internet End 59