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EEC-682/782Computer Networks I
Lecture 1
Wenbing [email protected]
(Lecture nodes are based on materials supplied by Dr. Louise
Moser at UCSB and Prentice-Hall)
Spring Semester 2005EEC-682: Computer Networks I
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Outline
SyllabusIntroduction to computer networks
DefinitionUses of computer networksNetwork hardwareNetwork
software
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Course ObjectivesBecome familiar with the basics of computer
networks
What is a computer networkWhat are the network architecturesWhat
are the fundamental protocols
Get some hands-on experiences Learn some basic network computing
techniques
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Outline of Lectures
Introduction to computer networksPhysical layerData link
layerMedium access control sublayerNetwork layerTransport
layerApplication layerNetwork security
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Outline of assignments
Assignment 1: Sockets for inter-process communicationLearn some
basic network programming skills
Assignment 2: Set up your Web homepageOptional project
Must be implementation related, potential projectsImplementation
of a group communication systemImplementation of a reliable
point-to-point transport service that resembles TCP in the user
space using UDPBuild a switch using a PC and a few network
interface cards
Can substitute for a midterm/final exam, or enhance your
grade
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Grading PolicyGrade components & relative weights:
Class participants: 5%Assignments: 20%
No group is allowed, must do the assignments independentlyLate
turn-in accepted, but with penalties
1st midterm exams: 25% (chapters 1-4)2nd midterm exams: 20%
(chapters 5-6)Final exam: 30% (chapters 1-8)Exams are all
closed-book closed-notesOptional project: can substitute one exam,
or 25% extra
Individual projectA demo, detailed report, and source code
required
Do not cheat!Do not copy other students homework, exams or
projectDo not copy someone elses work found on the Internet
Including project implementation and reportYou can quote a
sentence or two, but put those in quote and give referenceYou can
build your project or homework on top of open source libraries, but
again, you need to explicitly give acknowledgement and state
clearly which parts are implemented by you
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Reference TextsAndrew S. Tanenbaum :
Computer Networks4th Edition, Prentice-Hall, 2003
Richard Stevens:Unix Network Programming: Volume 1 Sockets and
XTI
2nd Edition, 1998
Andrew S. Tanenbaum and Marten van Steen:Distributed Systems:
Principles and Paradigms
Prentice-Hall, 2002
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Misc
Instructor:Dr. Wenbing Zhao
e-mail: [email protected] hours:
TTh 6:00-7:50pmOffice hours: TTh 4:00-6:00pm and by
appointment
Networking Lab (SH 306)Upon request, I can create account on the
lab machines for youCan remotely login
Course Web
site:http://academic.csuohio.edu/zhao_w/teaching/eec682.htmLecture
nodes and homework will be posted
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Introduction of Computer Networks
Uses of computer networksNetwork HardwareNetwork software
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Definition of Computer Network
Interconnected collection of autonomous computersInterconnected
able to exchange info via copper wire, fiber, microwaves,
satellites, etc.Autonomous act independentlySingle network vs.
network of networks
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Computer Network vs Distributed SystemDistributed system - A
collection of independent computers that appear to the users as a
single coherent system
software specifically designed to provide an integrated
computing facilityTwo aspects (1) independent computers and (2)
single system middleware
Computer network User must handle network management
explicitly
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Uses of Computer Networks
Business applicationsHome applicationsMobile usersSocial
issues
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Business Applications of Networks
Goals of using computer networks for businessResource
sharingProvide powerful communication medium among employeesDoing
business electronically with other companiesDoing business with
consumers over the Internet (e-commence)
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Resource SharingResource sharing
equipment, software programs, dataClient-server model
Server provides services for clientsA network with two clients
and one server.
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Client-Server Model
The client-server model involves requests and replies.
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Home Network Applications
Access to remote informationWWW, online newspapers, sports
news
Person-to-person communicationInstant messaging, chat room,
peer-to-peer communication/file sharing
Interactive entertainmentVideo on demand, game playing
Electronic commerceOnline banking, online auction, etc.
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Home Network Applications
In peer-to-peer system there are no fixed clients and
servers.
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Home Network Applications
Some forms of e-commerce.
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Mobile Network UsersWireless network
Portable office, military, taxis, trucksFixed wireless, mobile
wireless
Combinations of wireless networks and mobile computing
Future applicationsWireless parking meters, vending machine
inventory report, utility meter reading, merge of cell phones and
PDAs, m-commerce, personal area networks and wearable
computersSmart watches, smart dust
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Social Issues
Offending contentCopyright violationsSpamsVirusesWho is
responsible?
Network operator? Software provider? Users?What kind of control
is appropriate?
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Network Hardware
No generally accepted taxonomy. Two dimensionsTransmission
technologyScale
Transmission technologyBroadcast linksPoint-to-point links
(unicasting)
ScalePersonal area networksLocal area networksMetropolitan area
networksWide area networksThe Internet
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Classification by Scale
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Local Area Networks
LAN typically spans a room, a building or a campusLANs are
distinguished from other kinds of networks by three
characteristics
Size restricted in size => worst-case transmission time is
boundedTransmission technology typically using broadcast
Static and dynamic broadcast channel allocationTopology
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Local Area Networks
Two broadcast networks(a) Bus(b) Ring
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Metropolitan Area NetworksMAN covers a cityA metropolitan area
network based on cable TV.
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Wide Area Networks
Spans a large geographical area, often a country or
continentNetwork structure in WAN
Host or end systemCollection of machines that run user
(application) programs
Communication Subnet connects hostsTwo distinct components
Transmission lines move bits (circuits, channels, trunks)Routers
or switching elements that connect two or more transmission
lines
Two types of designsPoint-to-point channelsBroadcast
channels
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Wide Area Networks
Relation between hosts on LANs and the subnet.
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Wide Area Networks
Point-to-point channelsStore and forward or packet switchIf no
direct connection, must use intermediate switching elements where
store packets until required output line is free and then
forwardMany different topologies ring, star, tree, irregular
ring star tree irregular
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Wide Area Networks
A stream of packets from sender to receiver.
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Wide Area NetworksBroadcast channels
Sent by one, received by allAddress field specifies intended
destinations
Multicast if more than one destinationWhen machine receives
packet, checks address ignores if not for itTopologies
ringbus satellite
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Wide Area Networks
Broadcast channelsNeed to arbitrate simultaneous access to
mediumTwo approaches
Static Divide time into slots, use round robin strategyWaste
channel capacity when nothing to send
DynamicCentralized bus arbitration unit decides who goes
nextDecentralized each machine decides for itself
A B C A B C
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Wireless Networks
Categories of wireless networksSystem interconnectionWireless
LANsWireless WANs
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Wireless Networks(a) Bluetooth configuration(b) Wireless LAN
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Wireless Networks
(a) Individual mobile computers(b) A flying LAN
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Home Network CategoriesComputers
Desktop PC, PDA, shared peripheralsEntertainment
TV, DVD, VCR, camera, stereo, MP3Telecomm
Telephone, cell phone, intercom, faxAppliances
Microwave, fridge, clock, furnace, air conditionerTelemetry
Utility meter, burglar alarm, babycam
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Network SoftwareProtocol hierarchies / Network
architecturesDesign issues for the layersConnection-oriented and
connectionless servicesService primitivesThe relationship of
services to protocols
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Protocol HierarchiesProtocol hierarchies are organized into
layers or levels with different protocols at each layerEach layer
offers certain services to higher layers, hiding the details of
implementation of those servicesLayer n on one machine communicates
with layer n on another machineInterface between adjacent layers
defines operations and services offered by lower layer to upper
layer
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Protocol HierarchiesLayers, protocols, and interfaces.
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Network Architectures
Network Architecture - A set of layers and protocolsMust contain
enough information for implementationDoes not contain details of
the implementation and specification of the interfacesIt is not
even necessary that the interfaces on all machines in a network be
the same
Protocol Stack - A list of protocols used by a certain system,
one protocol per layerThe subjects of network architectures,
protocols stacks, and the protocols themselves are the principal
topics of this course
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Protocol HierarchiesThe philosopher-translator-secretary
architecture.
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Protocol HierarchiesExample information flow supporting virtual
communication in layer 5.
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Design Issues for the Layers
Each layer needsMechanisms for
connection establishment and addressingConnection termination or
release
Rules for data transferSimplex one directionHalf duplex either
direction, but not simultaneouslyFull duplex both directions
simultaneouslyNumber of logical channels and their priority
Error controlError detecting and correcting codesPositive and
negative acksRe-sequencing packets that arrives out of order
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Design Issues for the Layers
Each layer needsFlow control
Need to keep a fast sender from swamping a slow receiverUse
feedback from receiver to sender
Finite buffersInability of receiver to accept arbitrarily long
messagesUse mechanisms for disassembling, transmitting,
reassembling
MultiplexingSeveral unrelated conversations between pair of
communicating processes
RoutingWhich route to use if there are several
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Connection-Oriented and Connectionless Services
Connection-oriented serviceModeled after telephone system
establish connection before communicationSome service allow a
negotiation among sender, receiver and subnet regarding the
parameters to be used, such as max message size, etc.
Connectionless serviceModeled after postal system a message
carries full destination address, and each one is routed through
the system independent of all the others
Ordering of messages are not guaranteed
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Connection-Oriented and Connectionless Services
Quality of service characterize each serviceReliable service it
does not lose data
Implemented by having the receiver acknowledge the receipt of
each messageThe acknowledgement process introduces overhead and
delaysTwo variations
Message sequences message boundaries are preservedByte streams
message boundaries are not preserved
Example: file transferUnreliable connectionless service datagram
service
No acknowledgement is usedIn analogy with telegram service
Acknowledged datagram serviceLike sending a registered letter
and requesting a return receipt
Request-reply service used in client/server model
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Connection-Oriented and Connectionless Services
Six different types of service.
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Service Primitives
Five service primitives for implementing a simple
connection-oriented service.
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Service PrimitivesPackets sent in a simple client-server
interaction on a connection-oriented network.
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Relationship of Services to Protocols
Services and protocols are distinct conceptsA service is a set
of primitives (operations) that a layer provides to the layer above
it
Defines what operations the layer is prepared to perform on
behalf of its usersHow service is implemented is not revealed
(hidden)Relates to an interface between two layers, with lower
layer being the service provider and the upper layer being service
user
A protocol is a set of rules governing the format and meaning
ofthe packets, or messages that are exchanged by the peer entities
within a layer
Entities use protocols to implement their service
definitionsDifferent protocol could be used to provide the same
serviceProtocol and service are completely decoupled
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Relationship of Services to Protocols
The relationship between a service and a protocol.
