CPEG 419 COMPUTER COMMUNICATION NETWORKS

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CPEG 419 COMPUTER COMMUNICATION NETWORKS
Instructor Stephan Bohacek Course webpage
www.eecis.udel.edu/bohacek/classes/419 Email
bohacek_at_ee.udel.edu Office Evans 315 Phone
831-4274 TA Ignjat Kilibarda TAs email
cmpt_at_udel.edu
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CPEG 419

• Textbooks
• Require textbook W. Stallings, Data and Computer
  Communications, 6th edition, Prentice Hall.
• Other books
• Peterson and Davie, Computer Networks.
• Tanenbaum, Computer Networks.
• Grading
• Homework and quizzes (20)
• Midterm (20)
• Project (20)
• Final exam (40)
• Homework consist of short problems, programming
  and ns simulations.

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Who are you?

• Write the following on a piece of paper
• Name, email, Majors, Year.
• Why 419?
• Do you know what the Fourier transform is?
• Do you know how to program? (C, sockets?)
• Have you taken any probability?
• Circuits? What is an RC circuit?
• Do you know what ARP is?
• What is 10base-T?
• What is the speed of 10base-T?

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Course Objectives

• Basic understanding of computer networks and
  their protocols.
• OSIs 7 layer protocol stack and the TCP/IP
  protocol suite.
• Internet.
• LANs.

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Course Outline

• Introduction
• Basic concepts
• Layers
• OSI
• TCP/IP
• Physical Layer
• Data Link Layer
• MAC Layer
• Multiplexing
• LANs

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Outline (contd)

• Network Layer
• Routers versus bridges
• Routing and forwarding
• Addressing and subnetting
• Internetworking
• IP IPv4 and IPv6
• ICMP
• Internet routing RIP, OSPF, BGP
• IP Multicast

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Outline (contd)

• Transport Layer
• UDP
• TCP
• End-to-end argument
• Error control
• Flow and congestion control
• Security

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Outline (contd)

• Layer 5 and above
• DNS
• FTP
• E-mail
• SNMP
• HTTP
• Wireless networks (time permitting)

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Administration Issues

• How late can we start next Tuesday?
• Probably no class on Oct 3.

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Introduction

• Basic concepts
• Layers
• OSI
• TCP/IP

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Ubiquitous Computing

• Computers everywhere.
• Also means ubiquitous communication
• Users connected anywhere/anytime.
• PC, laptop, palmtop, cell phone, etc.

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Computer Network

• WHY?
• Provide access to local and remote resources
  (data/information, computing, etc.).
• Provide efficient communication (email, voice
  over IP, chatting, etc.)
• HOW?
• Collection of interconnected end systems
• Computing devices (mainframes, workstations, PCs,
  palm tops)
• Peripherals (printers, scanners, terminals,
  sensors).
• Applications location and platform transparency.

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Computer Networks (contd)

• Physical Components
• Nodes
• End systems (or hosts),
• Routers/switches/bridges, and
• Links
• twisted pair,
• coaxial cable,
• fiber,
• radio,
• etc.

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Computer Networks (contd)

• Protocols Protocols define a way for the
  physical components to work together.
• Applications The final result and end product
  of the network.

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The Internet Some History

• Late 1970s/ early 1980s the ARPANET (funded by
  ARPA).
• Connecting university, research labs and some
  government agencies.
• Main applications e-mail and file transfer.
• Features
• Decentralized, non-regulated system.
• No centralized authority.
• No structure.
• Network of networks.

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The Internet (contd)

• Early 1990s, the Web caused the Internet
  revolution the Internets killer app!
• Today
• Almost 60 million hosts as of 01.99.
• Doubles every year.

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How the Internet is designed

• Internet Society
• IAB
• IETF
• IRTF
• Internet draft -gt RFC -gt Internet standard
• There are many other standards that are also
  used, e.g., IEEE, ISO, ITU-T

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Network Architecture (chapter 2)

• Protocol layers divide and conquer.
• Main idea each layer uses the services from
  lower layer and provide services to upper layer.
• Higher layer shielded from the implementation
  details of lower layers.
• Interface between layers must be clearly defined
  services provided to upper layer.

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Network Layers in Action An Example
Goal Send a file from a web server (e.g.
yahoo.com) to a web client (e.g. your PC).
Application e.g. http server
Application e.g. http client
Transport Layer e.g. TCP source
Transport Layer e.g. TCP receiver
Network Layer IP
Network Layer IP
Network Layer
Network Layer
Link Layer e.g., CSMA/CD
Link Layer e.g., CSMA/CD
Link Layer
Link Layer
Link Layer
Physical Layer e.g., twisted pair
Physical Layer e.g., twisted pair
Physical Layer
Physical Layer
Physical Layer
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Approach 1 ISO OSI Model

• ISO International Standards Organization
• OSI Open Systems Interconnection.

Application
Presentation
Session
Transport
Network
Data link
Physical
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OSI ISO 7-Layer Model

• Physical layer transmission of bits/bytes. Deals
  with electric properties and encoding.
• Data link layer reliable transmission over
  physical medium synchronization, error control,
  flow control media access in shared medium.
• Network layer routing and forwarding congestion
  control internetworking.

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OSI ISO 7-Layer Model (contd)

• Transport layer error, flow, and congestion
  control end-to-end.
• Session layer manages connections (sessions)
  between end points.
• Presentation layer data representation.
• Application layer provides users with access to
  the underlying communication infrastructure.

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Example 2 TCP/IP Model

• Model employed by the Internet.

ISO OSI
Application
TCP/IP
Application
Presentation
Session
Transport
Transport
Internet
Network
Network Access
Data link
Physical
Physical
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TCP/IP Protocol Suite

• Physical layer same as OSI ISO model.
• Network access layer medium access and routing
  over single network.
• Internet layer routing across multiple networks,
  or, an internet.
• Transport layer end-to-end error, congestion,
  flow control functions.
• Application layer same as OSI ISO model.

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Physical Layer (Stallings Chap. 3-6)

• Sending raw bits/bytes/words across the wire.
• Point to point. No routing, no error correction
  (link layer).
• Objective Transmit a frame from a transmitter to
  receiver.

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Basic Concepts

• Signal electro-magnetic wave carrying
  information.
• Time domain signal as a function of time.
• Analog signal signals amplitude varies
  continuously over time, ie, no discontinuities.
• Digital signal data represented by sequence of
  0s and 1s (e.g., square wave).

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Digital vs. Analog Signals
Digital signals dont really exists. We interpret
analog signals as digital
digital signal
analog signal
0
1
0
0
1
0
0
0
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Bandwidth vs. Data Rate

• Q. What is the bandwidth of 10base-T ethernet?
• The data rate is 10Mbs (mega bits per second).
• The bandwidth maybe larger than 10Mhz.

Let x(t) be the analog signal broadcast.
The Fourier transform of x is
X(f) is the component of x that has frequency f
The bandwidth of x is the fBW such that X(f)
is small for f gt fBW
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Bandwidth vs. Data Rate
2
time domain signal
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
2.5
frequency domain signal
2
1.5
1
0.5
0
-0.5
0.98
0.99
1
1.01
1.02
1.03
4
x 10
A single pulse contains all frequencies!
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Bandwidth vs. Data Rate
Band-limited approximation of the digital signal
0 0 0 1 1 0 1 1 0
0
1
1
1
1
0
0
0
0
0
1
1
1
1
0
0
0
0
sample times
threshold
0.3 time the bit-rate
0.5 time the bit-rate
0
1
1
1
1
0
0
0
0
0
1
1
1
1
0
0
0
0
0
1
1
1
1
0
0
0
0
0.75 times the bit-rate
2 times the bit-rate
1 times the bit-rate
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Bandwidth vs. Data Rate
Suppose the digital signal is 0 1 0 1 0 1 0 1 0
1 And a bit is sent every T seconds.
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Fourier Series (Fourier Transform for periodic
signals)
Let x be periodic with period 2T
where
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Bandwidth vs. Data Rate
Suppose the digital signal is 0 1 0 1 0 1 0 1 0
1 And a bit is sent every T seconds.
The lowest frequency component is at ½ the data
rate. What is the lowest bandwidth of the signal
that might be able to approximate x?
Hence, to transmit a binary signal with data rate
1/T, one must use an analog signal that contains
frequencies up to ½?1/T.
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Multi-level Signals Bit Rate and Baud Rate

• The number of bits transmitted can be increased
  by transmitting more than one bit in one time
  slot
• Baud rate number of times per second signal
  changes its value (voltage).
• Each value might carry more than 1 bit.
• Example 8 values of voltage (0..7) each value
  conveys 3 bits, ie, number of bits log2V.
• Thus, bit rate log2V baud rate.
• For 2 levels, bit rate baud rate.

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Last slide
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Data Transmission 1

• Analog and digital transmission.
• Example of analog data voice and video.
• Example of digital data character strings
• Use of codes to represent characters as sequence
  of bits (e.g., ASCII).
• Historically, communication infrastructure for
  analog transmission.
• Digital data needed to be converted modems
  (modulator-demodulator).

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Digital Transmission

• Current trend digital transmission.
• Cost efficient advances in digital circuitry
  (VLSI).
• Advantages
• Data integrity better noise immunity.
• Security easier to integrate encryption
  algorithms.
• Channel utilization higher degree of
  multiplexing (time-division muxing).

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Communication Model
Network
Source
Destination
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Example
PTN
Modem
Modem
Source
Destination
Source System
Destination System
PTN Public Telephone Network
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Connecting End Systems
Dedicated link
Multiple access / shared medium
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Connecting End Systems (contd)
Router
Switched network
Router switching element a.k.a., IMPs
(Interface Message Processors) in ARPAnets
terminology.
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Shared Communication Infrastructure

• Shared medium
• Examples ethernet, radio.
• How to acquire channel medium access control
  protocols.
• Switched networks
• Shared infrastructure consisting of
  point-to-point links.
• Circuit- versus packet-switching.

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Circuit Switching

• Establish dedicated path (circuit) between source
  and destination.
• Example telephone network.
• s predictable usage of resources(stream-oriente
  d).
• -s lower resource utilization (e.g.,bursts).

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Packet Switching
S1
D1
D2
S2

• Data split into transmission units, or packets.
• Routers store packets briefly store packets and
  forward them store-and-forward.
• Efficient resource use statistical multiplexing.
• Ability to accommodate bursts.

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(Switched) Network Topologies
Ring
Tree
Star
Irregular
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Protocol

• Set of rules that allow peering entities to
  communicate.
• Example 2 friends talking on the phone.
• Peering entities or peers user application
  programs, file transfer services, e-mail
  services, etc.