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The Infrastructure Technologies Communication All communications require: Transmitters/Senders and receivers Transmission medium Rules of communication A message Transmitter Medium Message Receiver Computer Data Communication Transmitter/Receiver Combination of Hardware and software Physical Media Types Cable twisted pair coaxial cable fiber-optic cable Wireless media radio microwave cellular telephone satellite infrared Data Communication Media ■ Bandwidth ■ Measure of a medium’s carrying capacity Measured in bits (bps) Two categories Baseband one line, one channel most local communication Broadband one line, simultaneous channels DSL, cable Connection Type Bandwidth Local telephone line 56 Kbps Wireless 2G digital cellular 2.5G digital cellular 3G digital cellular Bluetooth Wi-Fi (802.11b) 19.2 Kbps 144 Kbps 2 Mbps 1 Mbps Up to 11 Mbps Home satellite service 400 Kbps DSL 1.44 Mbps Cable service 2 to 10 Mbps Leased line (T-1, T-3) 1.5 to 43 Mbps Fiber optic cable Up to 10 Gbps The Message Message Header Body Trailer Messages have header and trailer carry information for delivering and ensuring the integrity of the message These are used by application and communication protocols The electronic form of a message is a signal Protocols A precise set of rules for communicating A communication protocol defines: message format (header/trailer) communication speed How the message is encoded (e.g., ASCII, EBCDIC) filtering/error correction rules An implementation of standard rules for passing parameters between adjacent layers Signal Transmission Time + 0 Amplitude Cycle Cycle Frequency = cycles per unit of time Signals transmitted in the context of a Carrier Signal Known frequency Known amplitude Signal Incompatibility 1-bit 1-bit 0-bit 0-bit ■ Inside the computer must have discrete/digital ■ Many existing communication lines are continuous/analog (especially in the last mile) ■ Signal must be converted between digital/discrete and analog/continuous through modulation/demodulation. ■ The function of a modem Networks A network consists of two or more computers linked by communication lines. Connectivity – the ability of a device or software to work with other devices and/or software over a network connection Each connected device is called a node Local Area Network - LAN Small geographic scope Computers in close proximity Local communications no boosting or filtering Workstations Wide Area Network - WAN Network of networks Computers geographically disbursed Long-distance communication Enterprise networks Intranet Supply chain integration common carrier boost and filter signal Extranet Global networks Internetworking Hardware Use to connect multiple LANs or WANs Have intelligence to filter, route and do protocol conversion Examples Bridges - Similar Networks Gateways - Dissimilar networks Routers Switches Bridges and Gateways Workstation Workstation Workstation Workstation Workstation Server ■ A bridge links similar networks. ■ A gateway links dissimilar networks. Workstation Bridge Server Workstation Workstation Server Gateway Workstation Workstation Routers accept messages at one of several input ports and forward the message to the appropriate output port Router Out In Common Network Topologies Bus Ring Star Clients/Server Networks Client Client Server Printer Client File system Client Peer to Peer Networks Peer computer Peer computer File system File system Peer computer File system Peer computer File system Network Operating Systems ■ ■ Client/server architecture LANs The system software runs on the server Part of the NOS runs on each workstation Software that handles communication between the workstation and the NOS Server Agent process on client Network client’s link to network operating system Network Examples Novell NetWare Windows Server 2000, 2003, NT Server Peer to Peer Networks NOS is installed on each attached workstation Runs on top of the local operating system Client Windows ME Communication software Message Delivery ■ ■ Each computer or terminal is a node Messages (signals) are either ■ Broadcast to all nodes Or move from node to node (point to point) Topology or routing determines the route Protocols define the precise rules to follow for LAN access and message delivery (Many different protocol exist) ■ Popular LAN Access control methods Collision detection Token passing Network Access Control Methods ■ Distributed Access Control Token passing CSMA/CD (collision detection) ■ Circulating electronic token prevents collisions Must possess the token to transmit a message Random Access Control Eliminates collisions “Listen” for quiet line (carrier signal); then send message Collision occurs with simultaneous messages Must wait and resend Three major standard protocols for LANs Ethernet - (CSMA/CD, Star or Bus) Token-Ring - (Token passing, Ring) ARCnet - (Token passing, Star or bus) Packet Switching ■ ■ ■ ■ ■ Most popular type of message delivery Message A Packet A1 Packet A2 Packet A3 Packet A3 Packet B2 Packet X3 Packet A1 Packet Y1 Open Packet Z2 Packet A2 Packet Z1 Packet Y2 Packet X2 Open Open Packet Y3 Packet B1 Packet Packet Packet X1 Break message into packets Transmit packets independently Multiple messages share line Reassemble message at receiving end Packet A1 Packet A2 Message A Packet A3 Packet Switching ■ ■ Packets can follow different routes to reach destination Error handling is important ■ Packets can arrive out of order Individual packets may be lost Objectives Deliver the message accurately Efficient utilization of available bandwidth Efficient error recovery The TCP/IP Model Application layer TCP/IP is the standard packet switching protocol for the Internet Transport layer Internet layer Network access layer TCP/IP Layers ■ ■ Application layer protocols that directly support application programs protocols such as telnet, FTP, SMTP, DNS, POP, and HTTP Transport layer TCP (Transmission Control Protocol) creates packets and reassembles messages guarantees delivery Receiving end acknowledges each packet Sending end re-sends unacknowledged packets TCP/IP Layers (continued) ■ ■ Internet layer • IP (Internet Protocol) • routes and delivers individual packets Network access layer This is where Ethernet, Token ring and other network access protocols reside IP Address ■ IP address 32 bit number dotted decimal format 134.53.40.2 ■ Standards IPv4 – current: IPv4 addresses are 32 bits supports 232 (about 4.3 billion) addresses IPv6 – proposed: a 64-bit (sub-)network prefix and a 64bit host part ■ supports 2128 addresses Internet protocol communication requires IP address Assigning an IP Address ■ ■ ■ All computers attached to the Internet must have an IP address. Static allocation IP address established at installation linked to specific computer’s Media Access Control (MAC) address (i.e. Ethernet address) Dynamic allocation IP address allocated dynamically at login time Must use a protocol such as Dynamic Host Configuration Protocol (DHCP) Domains Domain aero biz com coop edu info gov mil museum name net org pro Signifies Air-transport industry Business organization US commercial Coooeratives US educational Unrestricted US government US military Museums Individuals US network US non-profit Professionals Domain au br ca cn de fi fr gb in it jp ru za Signifies Australia Brazil Canada China Germany Finland France Great Britian India Italy Japan Russia South Africa Domain Name System (DNS) • Accepts domain name • Converts to IP address • Network operating system routine on each host each server each Internet service provider (ISP) each network service provider (NSP ) Caching ■ Domain name and IP address cached by all participating Domain Name Systems. ■ Subsequent references use cached IP address. Business student uses cob Internet Architecture Network Service Provider (NSP) Network Access Point (NAP) Network Access Point (NAP) Network Service Provider (NSP) Regional Internet Service Provider Local ISP Regional Internet Service Provider Local ISP Regional Internet Service Provider Local ISP Internet Access ■ ■ ■ ■ ■ Access via local point of presence (POPs) by local call broadband access into the home ISPs provide access (the “on-ramp”) POPs connect up the network hierarchy to an interconnect point Phone is most common for individuals Broadband (Cable and ADSL) are coming fast...and competing for market share.