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Computer Communication
Networks
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Communications activity associated withdistributing or exchanging information
Telecommunications technology of communications at a distance that permitsinformation to be created any where and used
everywhere with little delay Today it, involves
Data: digital and analog (how analog data istransmitted?)
Voice: spoken word, music..
Video: telelcommunication imaging
Introduction
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Communication Services &Applications
A communication service enables the exchange of information between users at different locations. Communication services & applications are
everywhere .
E-mailserver Exchange of text messages via servers
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Communication Services &Applications
Web Browsing
Web server
Retrieval of information from web servers
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Communication Services &Applications
Instant Messaging
Direct exchange of text messages
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Communication Services &Applications
Telephone
Real-time bidirectional voice exchange
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Communication Services &Applications
Cell phone
Real-time voice exchange with mobile users
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Communication Services &Applications
Short Message Service
Fast delivery of short text messages
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SummarizingSummarizing
Two or more than two computersystems connected by means of acommunication medium like cables is
termed as a Network. Computer Network is a
communication system, which linkscomputers and their resources.
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Why we need Networking? Sharing of data and resources Distributing computation
among nodes Remote I/O devices To share data/files access.
Personal Communication (Chat,E-mail, now VOIP)
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BENEFITS OF A NETWORK BENEFITS OF A NETWORK
Following are the benefits of networking. Information Sharing
Printer Sharing Hard Disk Sharing Modem Sharing
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Hardware Sharing Software Sharing Service Access
Easy Back-Up Management Security Centralized Administration and
SupportNetworking helps to increase
the productivity
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Many other examples!
Peer-to-peer applicationsFile exchangeSearching for Extraterrestrial
Intelligence (SETI) Audio & video streaming Network games On-line purchasing Text messaging in PDAs, cell phones
(SMS) Voice-over-Internet
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What is a communicationnetwork?
The equipment (hardware & software) and facilities that provide the basiccommunication service
Virtually invisible to the user; Usually represented by a cloud
CommunicationNetwork
EquipmentRouters, servers,
switches,multiplexers, hubs,modems,
FacilitiesCopper wires,
coaxial cables,optical fiber
Ducts, conduits,telephone poles
How are communication networks designed and operated?
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Communication NetworkArchitecture
Network architecture : the plan thatspecifies how the network is built andoperated
Architecture is driven by the network services
Overall communication process is complex Network architecture partitions overall
communication process into separatefunctional areas called layers
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Networking: Why do we neednetworks?
Direct point-to-point communication is notalways possible/practical/efficient: Communicating entities can be too far apart for a single
link A large set of communicating entities (e.g. telephones)
would need impractically large number of connections
(full connectivity for N nodes needs N (N 1) / 2 links) Not all links would be needed all the time!
Solution isa communication network: Wide Area Network (WAN) Metropolitan Area Network (MAN)
Local Area Network (LAN)
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Network Architecture Evolution
1.0E+00
1.0E+02
1.0E+04
1.0E+06
1.0E+08
1.0E+10
1.0E+12
1.0E+14
1850 1875 1900 1925 1950 1975 2000
Telegraphnetworks
Telephonenetworks
Internet, Optical& Wireless
networks
Informationtransfer
persecond
NextGeneration
Internet
?
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Network Architecture Evolution
Telegraph NetworksMessage switching & digital transmission
Telephone NetworksCircuit SwitchingAnalog transmission digital transmissionMobile communications
InternetPacket switching & computer applications
Next-Generation InternetMultiservice packet switching network
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A Communication Model
Sourcegenerates data to be transmitted
TransmitterConverts data into transmittable signals
Transmission SystemCarries data
ReceiverConverts received signal into data
DestinationTakes incoming data
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Communications Tasks
Transmission systemutilization
Addressing
Interfacing Routing
Signal generation Recovery
Synchronization Message formatting
Exchange management Security
Error detection andcorrection
Network management
Flow control
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Simplified CommunicationsModel - Diagram
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Data Communication System Components
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Network Transmission Medium
Open air
radio, microwaves, satellites, infrared
noise signals, collision
Optical fiber
clear signals, low power and high rate (Gbps)
Copper wire
Lower cost interfacesBi-directional
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Whats a protocol?
human protocols: whats the time? I have a question introductions
specific msgs sent specific actions
taken when msgsreceived, or otherevents
network protocols: machines rather than
humans all communication
activity in Internetgoverned by protocols
protocols define format,order of msgs sent and received among network
entities, and actions taken on msg
transmission, receipt
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Whats a protocol?a human protocol and a computer network protocol:
Hi
HiGot thetime?2:00
TCP connection
reqTCP connectionresponseGet http://www.awl.com/kurose-ross
time
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Key Elements of a Protocol
SyntaxData formatsSignal levels
SemanticsControl informationError handling
TimingSpeed matchingSequencing
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Basic Concepts
Line Configuration Topology
Transmission Mode Categories of Networks Internetworks
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Point-to-Point Line Configuration
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Point-to-Point Line Configuration
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Point-to-Point Line Configuration
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Multipoint Line Configuration
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Networking
Point to point communication notusually practicalDevices are too far apartLarge set of devices would need
impractical number of connections Solution is a communications network
Wide Area Network (WAN)
Local Area Network (LAN)
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Mesh Network Topology
Type I - Nodes are arranged in gridseach node can talk to its neighbors directlynon-neighbor nodes needs store-and-forward
for communication
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Type II - Mesh Topology
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Star Network TopologyOne node at the center acts as the master nodeOther nodes linked to the master function as slaves
slaves communicate via master
easy to arbitrate among slaves (master decides)
not scalable (the master is the bottleneck)
normally for small networks or that requirespredictable performance
master failure shutdowns the whole net
Example: Ethernet, DSLMaster
slave
slave
slave
slave slave
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Star Topology
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Tree Topology
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Bus Network TopologyEvery node taps into a common mediumSignals may collide with each other
need to arbitrate who will get the bus
capable of broadcasting message (one send & many listen)
the common medium is the bottleneck
single node failure causes no network failure
the medium failure brings down the network
Example: (10BASE2, 10BASE5) Ethernet
common medium
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Bus Topology
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Ring Network Topology
Nodes are arranged in a ring One node receives from its predecessor & sends
to its successor arbitrate who can access the ring messages forwarded by each node sender deletes its messages from the ring the common ring is the single point of failure (complicated
connectors needed)
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Ring Topology
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Hybrid Network Topology
No restrictions on how to link the nodes Topology can adapt to individual organization
needs
Master
slave
slave
slave
slave slave
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Hybrid Topology
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Simplex
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Half-Duplex
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Full-Duplex
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Network Classification
Classification of interconnectedprocessors by scale.
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Network Types by Scope
WAN - wide area network cross large span of space (continental)
typically heterogeneous and low speed
example: Internet
MAN - metro-area network regional scope (city-wide)
LAN - local area network
limited scope (a couple of buildings)
typically homogeneous & high speed
example: Ethernet & Token ring
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Local Area Networks
Local area networks (LANs) areprivately-owned networks within asingle building or campus of up to afew kilometers in size.
LANs are distinguished by threecharacteristics: (Restricted in) Size Transmission technology: 10 Mbps to 10
Gbps (1 Mbps = 1,000,000 bits/sec, 1Gbps = 1,000,000,000 bits/sec).
Topology: bus and ring
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Local Area Networks
Two broadcast networks (a) Bus: Ethernet IEEE 802.3 (b) Ring: IEEE 802.5, FDDI
Local Area Network
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Local Area Network
Local Area Network
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Local Area Network
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LAN Configurations
SwitchedSwitched Ethernet
May be single or multiple switches
ATM LAN
Fibre Channel Wireless
MobilityEase of installation
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Metropolitan Area Networks
A metropolitan Area Networks (MAN)is a network that interconnects userswith computer resources in ageographic area or region such as acity.
Deployment Cable television Wireless: IEEE 802.16
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Metropolitan Area Networks
MAN Middle ground between LAN and
WAN
Private or public network High speed data transmission Large area coverage
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Metropolitan Area Networks
A metropolitan area network based oncable TV.
Metropolitan Area Network
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Metropolitan Area Network
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Wide Area Networks
A wide area network (WAN ) spans alarge geographical area, often a countryand continent.
It contains a collection of machines(hosts ).
The hosts are connected by acommunication subnet .
The subnet consists of two components: Transmission lines Switching elements: router
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Wide Area Networks
Relation between hosts on LANs and thesubnet.
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Wide Area Networks
Large geographical area Crossing public rights of way Rely in part on common carrier circuits
Alternative technologiesCircuit switchingPacket switchingFrame relay
Asynchronous Transfer Mode (ATM)
Wide Area Network
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Internetworks
Different networks are connected bymeans of machines called gateways .
A collection of interconnected networks
is called an internetwork or internet . A common form of internet is acollection of LANs connected by a WAN.
Internetwork
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Internetwork (Internet)
Networking
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NetworkingConfiguration
Wh t th I t t t d b lt
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Whats the Internet: nuts and boltsview
millions of connectedcomputing devices: hosts,end-systems PCs workstations, servers PDAs phones, toasters
running network apps
communication links fiber, copper, radio, satellite transmission rate bandwidth
routers: forward packets(chunks of data)
local ISP
companynetwork
regional ISP
router workstationserver
mobile
C l i t t li
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Cool internet appliances
Worlds smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html
IP picture frame
http://www.ceiva.com/
Web-enabled toaster + weather forecaster
Wh t th I t t t d b lt
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Whats the Internet: nuts and boltsview protocols control sending,
receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP
Internet: network of networks loosely hierarchical public Internet versus private
intranet
Internet standards RFC: Request for comments IETF: Internet Engineering Task
Force
local ISP
companynetwork
regional ISP
router workstationserver
mobile
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Whats the Internet: a service view communication
infrastructure enablesdistributed applications: Web, email, games, e-
commerce, database.,
voting, file (MP3) sharing communication servicesprovided to apps: connectionless connection-oriented
cyberspace [Gibson]:a consensual hallucination experienced daily by
billions of operators, in every nation, ...."
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Frame Relay
Packet switching systems have largeoverheads to compensate for errors Modern systems are more reliable
Errors can be caught in end system Most overhead for error control is stripped
out
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Asynchronous Transfer Mode
ATM Evolution of frame relay Little overhead for error control
Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching
technique
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Wireless Communication
Wireless communication is not anew idea.Native American smoke signal
Chinese Beacon fireWireless telegraph using Morse Code
Modern digital wireless systems
have better performance, but thebasic idea is the same.
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Wireless Networks
Categories of wireless networks:System interconnectionWireless LANsWireless WANs
System Interconnection
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System Interconnection
System interconnection is all aboutinterconnecting the components of acomputer using short-range radio.
Some companies got together to design ashort-range wireless network calledBluetooth to these components.
Bluetooth allows digital cameras, headsets,
scanners, and other devices to connect to acomputer is a short range.
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Bluetooth Standard
The Bluetooth document is adopted byIEEE (Institute of Electrical and ElectronicsEngineers) 802.15 as a basis for wirelesspersonal area networks.Work at 2.4 GHz Transfer up to 2 Mbps10 meters range
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Wireless Networks
(a) Bluetooth configuration (b) Wireless LAN
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Wireless LANS
The wireless local area networks (LANs)are systems in which every computer hasa radio modem and antenna with which itcan communicate with other systems.
Wireless LANs are common in small officesand homes.
There is a standard for wireless LANs,called IEEE 802.11 .
Wi l WANS
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Wireless WANS
The wireless wide area networks (WANs) aresystems used in the wide area. The radio network used for cellular
telephones is an example of a low-bandwidth (low transfer rate) wirelesssystem.First generation: analog for voice
Second generation: digital for voice Third generation: digital for voice and
data
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Wireless WANS
High-bandwidth wide area wirelessnetworks are also being developed. A standard for metropolitan area networks
(MANs), called IEEE 802.16 , has alsobeen developed .Work at 10-to-66 GHz Transfer up to 155 Mbps30 miles range
Wi l N k
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Wireless Networks
(a) Individual mobile computers (b) A flying LAN
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Wireless WANS
High-bandwidth wide area wirelessnetworks are also being developed. A standard for it, called IEEE 802.16 , has
also been developed.Work at 10-to-66 GHz Transfer up to 155 Mbps30 miles range
H N t k C t i
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Home Network Categories
Computers (desktop PC, PDA, sharedperipherals)
Entertainment (TV, DVD, VCR, camera,stereo, MP3)
Telecomm (telephone, cell phone,intercom, fax)
Appliances (microwave, fridge, clock,
furnace, airco) Telemetry (utility meter, burglar alarm,
babycam).
Home Network Properties
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Home Network Properties
The network and devices have to be easy to install. The network and devices have to be foolproof in operation. Low price is essential for success. The main application is likely to involve multimedia.
It must be possible to start out with one or two devices andexpand the reach of the network gradually.
Security and reliability will be very important .
A closer look at network
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structure:
network edge: applicationsand hosts
network core: routers
network of networks
access networks, physicalmedia: communication links
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Circuit Switching
Dedicated communications pathestablished for the duration of theconversation
e.g. telephone network
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Packet Switching
Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node
between source and destination Used for terminal to computer and
computer to computer communications
Data Communication
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Frameworks
Two major data communicationframeworks have been developed to helpensure that networks meet business andcommunication requirements:Open Systems Interconnection (OSI) reference
model developed by the InternationalStandards Organization (ISO)
Transmission Control Protocol/Internet Protocol(TCP/IP) suite
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Transmission Speeds
Medium Speed CostTwistedWire 300bps-10Mbps LowMicrowave 256Kbps-100Mbps
Satellite 256Kbps-100MbpsCoaxial Cable 56Kbps-200MbpsFiber-Optic Cable 500Kbps-10Gbps High
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Important Standard-Setting
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Organizations
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Online System Requirements
Response Time Throughput Consistency Flexibility
Online Systems Requirements
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Continued
Availability ReliabilityMean time between failure (MTBF)Mean time to repair (MTTR)Fault Tolerance
Recovery Security
Business Data Communication
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Applications
Major data communication applicationsinclude:E-mailGroupware
Knowledge management systemsE-commerce and e-business applicationsWireless applications
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Groupware Applications
Group calendarsystems Electronic filing
cabinets Project
managementsoftware
Group supportsystems
Electronic meetingandvideoconferencingsystems
Documentmanagementsystems (imageprocessingsystems)
Other Data Communication
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Applications
Batch applications Data entryapplications
Distributedapplications
Inquiry/responseapplications
Interactiveapplications Sensor-based
applications Combined
applications
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Application Service Providers
Many businesses have turned to third-party services for some or all of theirbusiness and data communicationsapplications
Application service providers (ASPs) arethird-party organizations that manage anddistribute software and services to othercompanies over the Web
Many ASPs specialize in integrated e-commerce and e-business applications
Business Data Communications
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Issues Major data communications issues
include:Cost-effectiveness The InternetBandwidthEvolving technologiesConvergenceStandards
Privacy and security
Services versus Throughput Rates
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