Transcript EE/CS 450 Introduction to Networks

CPEG 419
COMPUTER COMMUNICATION
NETWORKS
Instructor: Stephan Bohacek
Course webpage:
www.eecis.udel.edu/~bohacek/classes/
419
Email: [email protected]
Office: Evans 315
Phone: 831-4274
TA: Ignjat Kilibarda
TA’s email: [email protected]
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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.
OSI’s 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 (cont’d)
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 (cont’d)
Transport Layer
UDP
TCP
End-to-end argument
Error control
Flow and congestion control
Security
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Outline (cont’d)
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
(cont’d)
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
(cont’d)
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 1970’s/ early 1980’s: 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 (cont’d)
Early 1990’s, the Web caused the Internet
revolution: the Internet’s 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 -> RFC -> 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
Link Layer
e.g., CSMA/CD
Physical Layer
e.g., twisted pair
Network Layer
Link Layer
Link Layer
Link Layer
Physical Layer
Physical Layer
Physical Layer
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Link Layer
e.g., CSMA/CD
Physical Layer
e.g., twisted pair
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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
(cont’d)
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.
TCP/IP
Application
Transport
Internet
Network
Access
Physical
Application
Presentation
ISO OSI
Session
Transport
Network
Data link
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: signal’s amplitude varies
continuously over time, ie, no discontinuities.
Digital signal: data represented by sequence
of 0’s and 1’s (e.g., square wave).
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Digital vs. Analog Signals
Digital signals don’t really exists. We interpret analog signals as digital
1.4
1.2
1
analog
signal
0.8
0
0.6
0
1
0
0
1
0
0
digital
signal
0.4
0.2
0
0
10
20
30
40
50
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Bandwidth vs. Data Rate
Q. What is the bandwidth of 10base-T ethernet?
A. 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 

 jwt 2


x
t
e
dt


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 > fBW
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Bandwidth vs. Data Rate
2
time
domain
signal
 1 for t  T
xt   
0 otherwise
1.5
1
0.5
0
0
10
20
30
40
50
60
70
80
90
2.5
frequency
domain
signal
Xf 
sin Tf 
f
2
1.5
1
0.5
0
-0.5
0.98
0.99
1
1.01
1.02
1.03
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 0 0 1 1 0 1 1 0
2
0 0 0 1 1 0 1 1 0
sample times
2
threshold
0
0
5
4
3
2
1
0
1
2
3
4
5
5
0.3 time the bit-rate
2
1
0
1
2
3
4
5
0.5 time the bit-rate
2
000110110
1.5
1
1
1
0.5
0.5
0
0
0
0.5
3
000110110
000110110
1.5
4
5
4
3
2
1
0
1
2
3
4
0.75 times the bit-rate
5
1
0.5
5
4
3
2
1
0
1
2
3
4
1 times the bit-rate
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4
3
2
1
0
1
2
3
5
2 times the bit-rate
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4
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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.
1 for 2kT  t  2k  1T
xt   
where k  ..., - 2, - 1, 0, 1, 2, ...
otherwise
0
xt  
1
1
 n

 
sin 
2t 
2 n 1,3,5,... n
 2T

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Fourier Series
(Fourier Transform for periodic signals)
Let x be periodic with period 2T

 n

 n

xt   a 0   a n cos
2t   bn sin 
2t 
 2T

 2T

n 1
where
1
a0 
2T
1
an 
T
 nt 


x
t
cos

dt
T
 T 
T
 xt dt
T
T
1
bn 
T
 nt 


x
t
sin

dt
T
 T 
T
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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.
1 for 2kT  t  2k  1T
xt   
where k  ..., - 2, - 1, 0, 1, 2, ...
otherwise
0
1
1
 n

 
sin 
2t 
2 n 1,3,5,... n
 2T

n1
1
The component at frequency
is
2 T n
xt  
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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