The Infrastructure Technologies

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

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 Computer Data Communication

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 Electromagnetic spectrum (Fig ) 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

As Signal Moves Over Line Signal degrades or loses strength. –Called attenuation Signal picks up noise. –EMI - Electromagmetic interference –Static –If not addressed, noise can overwhelm signal These limit the distance of some communications

Digital vs. Analog Analog –contiguous signal –amplify to boost signal  noise amplified, too  noise accumulates –filter known or predictable noise  tape hiss Digital –discrete signal  digits (0, 1) –sample/retransmit  boosts signal  automatically filters most noise  errors function of sampling rate Both digital and analog data are transmitted in the context of a carrier signal.

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 (The server’s operating system) –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 2000 Server Windows NT 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 (collison 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 Open Systems Interconnect (OSI) Model

Message Flow Physical Medium Application Presentation Session Transport Network Data link Physical Display and manipulate worksheet Decrypt and decompress worksheet Drop connection on completion Reassemble packets Verify delivery of entire message Reroute if necessary Accept packets Medium of transmission Receiving computer Excel worksheet created Worksheet encrypted and compressed Establish connection Divide into packets and create messages Determine packet routing Transmit one packet to next node Medium of transmission Sending computer Each level “talks to” the equivalent level on the other node. Transmission errors call for retransmission of affected packet or packets.

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

TCP/IP Layers Application layer –corresponds to OSI Application and Presentation layers –protocols that directly support application programs –protocols such as telnet, FTP, SMTP, DNS, POP, and HTTP Transport layer –corresponds to OSI Session and Transport layers –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 corresponds to OSI Network layer IP (Internet Protocol) routes and delivers individual packets Network access layer –corresponds to OSI Data-link and Physical layer –This is where Ethernet, Token ring and other network access protocols reside

TCP/IP Layers (continued)

IP Address IP address –32 bit number –dotted decimal format – Standards –IPV4 – current –IPV6 – proposed 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 (ie. 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 History 1960s Started as ARPANET (Advanced Research Projects Agency) 1986 NSFNET became internet Backbone (56Kbps) 1989 NSFNET upgraded to T (Mbps) 1991 NSFNET upgradet to T3 45 (Mbps) First commercial traffic First Web browser introduced 1995 NAPs Replaced NSFNET Control turned over to independent governing bodies

Internet Terminology Interconnect Level Any means for bandwidth providers to interconnect Network Access Points (NAPS) MAEs, FIXs and CIX (pseudo NAPs) Network Service Providers NSPs (National Backbone Providers) Replaced NSFNET (old backbone network) high-speed lines or series of connections that form the major pathways of the internet Regional Networks –connect up to one or more national backbone providers Local Internet Service Providers (ISPs) Consumers and Businesses –Servers - Contain information and are located on independently owned networks

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.