The Infrastructure Technologies

Communication All communications require: Transmitters/Senders and receivers Transmission medium Rules of communication A message

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

The Message 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 Signals transmitted in the context of a Carrier Signal Known frequency Known amplitude

Signal Incompatibility ■ 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 1-bit 0-bit 1-bit

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  common carrier  boost and filter signal Enterprise networks  Intranet Supply chain integration  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 ■ A bridge links similar networks. ■ A gateway links dissimilar networks.

Routers accept messages at one of several input ports and forward the message to the appropriate output port

Common Network Topologies

Clients/Server Networks

Peer to Peer Networks

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 Agent process on client client’s link to 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 Network operating system Windows ME Communication software ServerClient Network

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 Circulating electronic token prevents collisions Must possess the token to transmit a message Random Access Control Eliminates collisions  CSMA/CD (collision detection) “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 ■ Break message into packets ■ Transmit packets independently ■ Multiple messages share line ■ Reassemble message at receiving end

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 TCP/IP is the standard packet switching protocol for the Internet

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  ■ Standards  IPv4 – current : IPv4 addresses are 32 bits supports 2 32 (about 4.3 billion) addresses  IPv6 – proposed: a 64-bit (sub-)network prefix and a 64- bit host part supports 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 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

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.