The Infrastructure Technologies

Communication

. .

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

Transmitter ReceiverMediumMessage

• 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

Connection Type Bandwidth

Local telephone line 56 Kbps

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

Wireless2G digital cellular2.5G digital cellular3G digital cellularBluetoothWi-Fi (802.11b)

19.2 Kbps144 Kbps2 Mbps1 MbpsUp to 11 Mbps

The MessageMessage

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

C yc le C yc le

+

0

-

T im e

A m p litu d e

F req u en cy = cyc le s p e r u n it o f tim e

Electromagnetic spectrum

(Fig. 13.14)

• 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 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.

ServerBridge

Gateway

Server

WorkstationWorkstation

Workstation

Server

WorkstationWorkstation

Workstation

WorkstationWorkstation

Workstation Workstation

Routers

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

In

Out

Router

Common Network Topologies

Ring

Bus

Star

Clients/Server Networks

File system

Printer

Server

Client Client

Client Client

Peer to Peer Networks

Filesystem

Filesystem

Filesystem

FilesystemPeer computer Peer computer

Peer computer

Peercomputer

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

Networkoperating system Windows ME

Communicationsoftware

Server Client

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 A1 Packet A2 Packet A3

Message A

Packet A1 Packet A2 Packet A3

Message A

Packet A3 Packet B2 Packet X3

Packet Z2 Packet A2 Packet Z1

Open Packet Y3 Packet B1

Packet A1 Packet Y1 Open

Packet Y2 Packet X2 Open

Packet Packet Packet X1

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

OSI layer Responsibilities

Application Provides a logical link between an application program andthe lower-level protocols.

Presentation Performs necessary data representation and/or syntaxconversions; e.g., encryption/decryption.

Session Establishes, maintains, and terminates a connection.

Transport Breaks the message into packets. Ensures error free, end-to-end delivery of the complete message.

Network Determines the best route for sending a packet from thesource node to the destination node.

Data-link Formats a packet for transmission to the next node.

Physical Interfaces with the physical communication medium.

The first four layers work with the user's message.

The bottom three layers work with packets and control the network.

Message Flow PhysicalMedium

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

Application layer

Transport layer

Internet layer

Network access layer

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)

FTP requestFTP

headerTCP

headerIP

header

TCPheader

FTP requestFTP

header

FTP requestFTPheader

FTP requestApplication program

Application layer

Transport layer (each packet)

Internet layer(each packet)

FTP requestFTPheader

TCPheader

IPheader

Networkheader

Network accesslayer

IP Address

• IP address– 32 bit number– dotted decimal format– 134.53.40.2

• 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 Signifies Domain Signifies aero Air-transport industry au Australia biz Business organization br Brazil com US commercial ca Canada coop Coooeratives cn China edu US educational de Germany info Unrestricted fi Finland gov US government fr France mil US military gb Great Britian museum Museums in India name Individuals it Italy net US network jp Japan org US non-profit ru Russia pro Professionals za 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 History

• 1960s Started as ARPANET (Advanced Research Projects Agency)

• 1986 NSFNET became internet Backbone (56Kbps)

• 1989 NSFNET upgraded to T1 1.44 (Mbps)

• 1991 NSFNET upgradet to T3 45 (Mbps)

• 1991 - First commercial traffic

• 1994 - First Web browser introduced

• 1995 NAPs Replaced NSFNET

• 1995 - 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 ArchitectureNetwork Service Provider (NSP)

NetworkAccess Point

(NAP)

NetworkAccess Point

(NAP)

Network Service Provider (NSP)

Regional InternetService Provider

Regional InternetService Provider

Regional InternetService Provider

Local ISP Local ISPLocal 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.