cpeg 419 computer communication networks

U of D CPEG 419 1

CPEG 419 COMPUTER COMMUNICATION

NETWORKS

Instructor: Stephan BohacekCourse webpage:

www.eecis.udel.edu/~bohacek/classes/419

Email: [email protected]: Evans 315Phone: 831-4274TA: Ignjat KilibardaTA’s email: [email protected]

mailto:[email protected]

University of Delaware CPEG 419 2

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.


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?


Course Objectives:

Basic understanding of computer networks and their protocols.

OSI’s 7 layer protocol stack and the TCP/IP protocol suite.

Internet.LANs.


Course OutlineIntroduction

Basic concepts Layers

OSITCP/IP

Physical LayerData Link LayerMAC Layer

Multiplexing LANs


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


Outline (cont’d)

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

Security


Outline (cont’d)

Layer 5 and above DNS FTP E-mail SNMP HTTP

Wireless networks (time permitting)


Administration Issues

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


Introduction

Basic conceptsLayers

OSI TCP/IP


Ubiquitous Computing

Computers everywhere.Also means ubiquitous

communication Users connected anywhere/anytime. PC, laptop, palmtop, cell phone, etc.


Computer NetworkWHY?

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.


Computer Networks (cont’d)

Physical Components: Nodes

End systems (or hosts),Routers/switches/bridges, and

Links twisted pair, coaxial cable, fiber, radio,etc.


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.


The Internet: Some HistoryLate 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.


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.


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


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.


Network Layers in Action: An ExampleGoal: Send a file from a web server (e.g. yahoo.com) to a web client (e.g. your PC).

Applicatione.g. http server

Transport Layere.g. TCP source

Network Layer: IP

Link Layere.g., CSMA/CD

Physical Layere.g., twisted pair

Network Layer

Link Layer

Physical Layer

Link Layer

Physical Layer

Network Layer

Link Layer

Physical Layer

Applicatione.g. http client

Transport Layere.g. TCP receiver

Network Layer: IP

Link Layere.g., CSMA/CD

Physical Layere.g., twisted pair


Approach 1: ISO OSI Model

ISO: International Standards Organization

OSI: Open Systems Interconnection.

Physical

Data link

Network

Transport

Session

Presentation

Application


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.


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.


Example 2: TCP/IP Model

Model employed by the Internet.

Physical

Data link

Network

Transport

Session

Presentation

ApplicationApplication

Transport

Internet

NetworkAccess

Physical

TCP/IP ISO OSI


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.


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.


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).


0 10 20 30 40 50 60 700

0.2

0.4

0.6

0.8

1

1.2

1.4

Digital vs. Analog Signals

Digital signals don’t really exists. We interpret analog signals as digital

0 1 0 0 1 0analogsignal

digitalsignal

0 0


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.

dtetxfX jwt 2The 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 > fBW



0 10 20 30 40 50 60 70 80 900

0.5

1

1.5

2

timedomain signal

otherwise 0

tfor 1 Ttx

frequency domain signal

f

TffX

sin

0.98 0.99 1 1.01 1.02 1.03

x 104

-0.5

0

0.5

1

1.5

2

2.5

A single pulse contains all frequencies!


Bandwidth vs. Data RateBand-limited approximation of the digital signal 0 0 0 1 1 0 1 1 0

0.3 time the bit-rate

0 1 111 0000

5 4 3 2 1 0 1 2 3 4 50.5

0

0.5

1

1.50 1 111 0000

0.75 times the bit-rate5 4 3 2 1 0 1 2 3 4 5

1

0

1

2

0 1 111 0000

1 times the bit-rate

5 4 3 2 1 0 1 2 3 4 50.5

0

0.5

1

1.50 1 111 0000

2 times the bit-rate

5 4 3 2 1 0 1 2 3 4 5

0

2 sample times

threshold

5 4 3 2 1 0 1 2 3 4 5

0

2

0 1 111 0000

0.5 time the bit-rate



Suppose the digital signal is … 0 1 0 1 0 1 0 1 0 1 … And a bit is sent every T seconds.

... 2, 1, 0, 1,- 2,- ..., where

otherwise 0

122for 1

kTktkT

tx

,...5,3,1

22

sin1

2

1

n

tT

n

ntx


Fourier Series (Fourier Transform for periodic signals)

10 2

2sin2

2cos

nnn t

T

nbt

T

naatx

Let x be periodic with period 2T

where

T

Tdttx

Ta

2

10

T

Tn dtT

tntx

Ta

cos

1

T

Tn dtT

tntx

Tb

sin

1


Bandwidth vs. Data RateSuppose the digital signal is … 0 1 0 1 0 1 0 1 0 1 … And a bit is sent every T seconds.

... 2, 1, 0, 1,- 2,- ..., where

otherwise 0

122for 1

kTktkT

tx

,...5,3,1

22

sin1

2

1

n

tT

n

ntx

n

1 is

T

1

2

nfrequency at component The

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 signalthat contains frequencies up to ½1/T.


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.


Last slide

cpeg 419 computer communication networks

Documents

computer communications

network of networks

computer networkwhy

internet revolution

internet contdearly

outline contdlayer

main applications

end product