Copyright 2006 Jim Martin1 Computer Communications Dr. Jim Martin [email protected].

Copyright 2006 Jim Martin 1

Computer Communications

Dr. Jim [email protected]


Web browsers and servers

InternetInternet

Internet Explorer,FireFox

www.usatoday.com

BellSouthBellSouth

HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"

Returns the web object. File size rangesReturns the web object. File size rangesFrom 20 bytes to gigabytesFrom 20 bytes to gigabytes



InternetInternet


www.usatoday.com

BellSouthBellSouth

Data sent between computers is packaged in packets.Data sent between computers is packaged in packets.TCP/IP refers to the set of protocols that defines the rules for TCP/IP refers to the set of protocols that defines the rules for sending and receiving packetssending and receiving packets


Data Communications


www.usatoday.com

Access Link:Dialup, DSL, Cable

Modem routers

Links


Data Communications

How does a computer send data to another computer?

1. They need a physical connection (called a link).2. Data is encoded and transmitted as energy.3. Energy is decoded at the destination back into data.4. Each form of energy has different properties which explains why some

connections are high speed and other connections are slow


Data Communications

Simplest approach - use varying voltages to represent 1s and 0s

One common encoding use negative voltage for 1 and positive voltage for 0

In following figure, transmitter puts positive voltage on line for 0 and negative voltage on line for 1


Back to the binary number system Let’s say one computer transmits the

message ‘hello’ to another computer. Each letter is mapped to a unique

number in the range of 0 to 255. The mapping is called the ascii character set:

Decimal Character

97 a98 b ….122 z

Decimal Character

48 049 150 2 ….57 9

Decimal Character

65 A66 B ….90 Z


Back to binary When ‘hello’ gets sent, the following decimal

numbers are sent: 104 101 108 108 109 We have now seen the message ‘hello’ in two

formats: ascii and decimal Remember what decimal format means:

A decimal number is a number (e.g., 104) that has a number of digits with the value of each digit ranging from 0 to 9.

Each digit represents some number of 1’s, 10’s, 100’s , …

Example: 104 in decimal: (1 * 100) + (0 * 10) + (4 * 1) = 104


Back to the binary number system Binary numbers are a number system made up of 0's and 1's. In base-10, the weight of each digit is based on 10EXP#digit

Digit# 3 2 1 0 1000 100 10 1

The magnitude of the first 8 places in binary notation are given by 2EXPdigit# (i.e., a base-2 number system and the digits are referred to as bits):

Bit# 7 6 5 4 3 2 1 0 128 64 32 16 8 4 2 1

Example: The number 10 interpreted in decimal is (1 * 10) + (0 * 1) = 10 (in decimal) The number 10 interpreted in binary is (1 * 2) + (0 * 1) = 2 (in decimal)

Example The number 13 in decimal is (1 * 10) + (3 * 1) = 13 (in decimal) The number 13 in binary does not exist. Digits must by 1’s and 0’s To convert the decimal number 13 to binary: (1 * 8) + (1 * 4) + (1 * 2) + (1 * 1) = 13

More examples of converting between binary and decimal systems: 0x00000010 = 2 in decimal 0x00000100 = 8 in decimal 0x10000010 = 130 in decimal 0x11111111 = 255 in decimal


Back to the binary number system The ascii message : hello

In ascii format: hello In decimal format : 104 101 108 108 109 In binary format: 1101000 1100101 1101100 1101100 1101101

Each character requires 8 bits

hello

11010001100101 1101100 1101100 1101101

hello

The least significant bit of the first character of the message is the first bit that is sent and the first bit that is received

The most significant bit of the last character (the ‘o’) is the last bit that is sent and the last bit that is received



InternetInternet


www.usatoday.com

BellSouthBellSouth

HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"

Returns the web object. File size rangesReturns the web object. File size rangesFrom 20 bytes to gigabytesFrom 20 bytes to gigabytes

The time from when the browserSends the message until when allThe data is received is theresponse time.


Where do the delays come from? Transmission time: time to transmit the

message over a link. T-t : message size in bits / link speed

(bits) bits per second

Propagation delay : Time for the bit to propagate over the physical medium. Electro-Magnetic energy travels at the

speed of light. E.g., propagation delay from NY to LA is

about .003 seconds.


Ping program Ping is an Internet program that tests if a

machine is alive. Also let’s us test the RTT and the loss rate between

two machines. All computers have the ping program.

However not all computers will reply.

Ping request msg

Ping reply msg


Ping: RTT calculation Two computers connected by a 64000 bps link. The one – way propagation delay over the link

is .003 seconds. What RTT would you expect if a 64 byte

message is sent and echoed back?

RTT= 2 * transmission delay + 2 * propagation delay = 2 * ( (64 * 8) / 64000) + 2 * (.003) = 2 * (.008) + 2 * (.003) = .022 seconds


Assessing application performance

When downloading a file the throughput is used to assess performance: Throughput: how much data is sent

in a given time. Download a 10,000 byte file in .060

seconds Throughput = 10,000 * 8 / .060 = 1.33

megabits per second (1.33 Mbps)


History of the Internet

Goal:To function if

part of network were disabled

Became functional

September 1969

ARPANET

Networking project by Pentagon’s Advanced

Research Projects Agency (ARPA)Goal:

To allow scientists at different

locations to share information


History of the InternetToday

More than 400 million host nodes

1984More than 1,000 host nodes

1969Four host nodes


Who controls the Internet?

World Wide Web Consortium (W3C)

Oversees research, sets standards and guidelines

Tim Berners-Lee, director

Internet2 (I2) Internet-related research

and development project

Develops and tests advanced Internet technologies

No onec—cit is a public, cooperative, andindependent network

Several organizations set standards


Internet names and addresses

The Internet Protocol (IP) defines many of the rules that make the Internet work. IP requires all computers on the Internet have an IP address.

A 32 bit (4 bytes) quantity Every computer must have a different IP address.

You might here about an IP address shortage… There are only 4,294,967,296 unique IP addresses (according to http://www.ibiblio.org/lunarbin/worldpop there are just over 6.6 billion

people- so everyone can not have their own IP address)

To find the IP address of a Windows machine, Go to start, control panel, network and Internetconnections, network connections and click the rightButton on the Local Area network connection andSelect status. You will see this panel of information.The default gateway is the IP address of a machineNearby that helps your machine connect to the Internet.


Internet names and addresses

The Internet Protocol (IP) defines many of the rules that make the Internet work. All computers on the Internet have an IP address What is a domain name?

Number that uniquely identifies each computer or device connected to Internet

Some computers have a domain name that is mapped to the computers IP address Domain Name: www.google.com Address in dotted decimal format: 216.239.39.99 Address in binary:

11011000 11101111 00101001 01100011


High-speed connection

High-speed connection

Slow-speed technology

Slow-speed technology

How to connect …

Dial-up accessmodem in your computer uses a

standard telephone line to connect to the Internet

Dial-up accessmodem in your computer uses a

standard telephone line to connect to the Internet

Digital subscriber line (DSL), cable telephone Internet

services (CATV), cable modem,fixed wireless, and satellite modems

Digital subscriber line (DSL), cable telephone Internet

services (CATV), cable modem,fixed wireless, and satellite modems

Connection is always on—whenever the computer

is running

Connection is always on—whenever the computer

is running

Connection must be established each time you log on. Slow but inexpensive

Connection must be established each time you log on. Slow but inexpensive


Broadband Access:DSL DSL is a very high-speed connection that uses the same

wires as a regular telephone line. Provided by an Internet Service Provider (ISP)

Here are some advantages of DSL: •You can leave your Internet connection always on and still use the phone line for voice calls. •Doesn't require new wiring. •Provides asymmetric high speeds: up to 6Mbps downstream and 768,000 upstream.

But there are disadvantages: •A DSL connection works better when you are closer to the provider's central office. •The connection is faster for receiving data than it is for sending data over the Internet. •The service is not available everywhere.


Broadband Access: WiMAX

WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.

No wires needed between a house and the ISP.

House can be 10 miles from the tower.

Provides access speeds from 1 Mbps to 70 Mbps depending on range and terrain.


Broadband Access + Home Networks: SECURITY Issues

Security issues Hacking : someone from the outside can hack into your

systems preventing your network from working Attacks on machines connected to your home network

Viruses that can delete your files Spyware that your files to the outside world Programs that can force your computer to attack other

computers

Your computer or home network must have these three security components:

Anit-spyware software: Spy bot, ad aware or Microsoft’s SpyWare Defender

Anti-virus software : Norton’s Antivirus, McAfee VirusScan Firewall : Norton’s Internet Security, zone labs, or

purchase a broadband router ($30 Linksys boxes come with a firewall).

Date post:	26-Dec-2015
Category:	Documents
Upload:	lester-armstrong
View:	215 times
Download:	1 times

Copyright 2006 Jim Martin1 Computer Communications Dr. Jim Martin [email protected].

Documents