Copyright 2006 Jim Martin1 Computer Communications Dr. Jim Martin

Copyright 2006 Jim Martin2 Web browsers and servers Internet Internet Explorer, FireFox BellSouth HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0" Returns the web object. File size ranges From 20 bytes to gigabytes

Copyright 2006 Jim Martin3 Web browsers and servers Internet Internet Explorer, FireFox BellSouth Data sent between computers is packaged in packets. TCP/IP refers to the set of protocols that defines the rules for sending and receiving packets

Copyright 2006 Jim Martin4 Data Communications Internet Explorer, FireFox Access Link: Dialup, DSL, Cable Modemrouters Links

Copyright 2006 Jim Martin5 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

Copyright 2006 Jim Martin6 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

Copyright 2006 Jim Martin7 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 a 98 b …. 122 z Decimal Character … Decimal Character 65 A 66 B …. 90 Z

Copyright 2006 Jim Martin8 Back to binary When ‘hello’ gets sent, the following decimal numbers are sent: 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

Copyright 2006 Jim Martin9 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# 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# 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: 0x = 2 in decimal 0x = 8 in decimal 0x = 130 in decimal 0x = 255 in decimal

Copyright 2006 Jim Martin10 Back to the binary number system The ascii message : hello In ascii format: hello In decimal format : In binary format: Each character requires 8 bits hello 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

Copyright 2006 Jim Martin11 Web browsers and servers Internet Internet Explorer, FireFox BellSouth HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0" Returns the web object. File size ranges From 20 bytes to gigabytes The time from when the browser Sends the message until when all The data is received is the response time.

Copyright 2006 Jim Martin12 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.

Copyright 2006 Jim Martin13 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

Copyright 2006 Jim Martin14 Ping: RTT calculation Two computers connected by a 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

Copyright 2006 Jim Martin15 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)

Copyright 2006 Jim Martin16 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

Copyright 2006 Jim Martin17 History of the Internet Today More than 400 million host nodes 1984 More than 1,000 host nodes 1969 Four host nodes

Copyright 2006 Jim Martin18 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 one c — c it is a public, cooperative, and independent network  Several organizations set standards

Copyright 2006 Jim Martin19 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 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 Internet connections, network connections and click the right Button on the Local Area network connection and Select status. You will see this panel of information. The default gateway is the IP address of a machine Nearby that helps your machine connect to the Internet.

Copyright 2006 Jim Martin20 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: Address in dotted decimal format: Address in binary:

Copyright 2006 Jim Martin21 High-speed connection Slow-speed technology How to connect … Dial-up access modem 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 Connection is always on— whenever the computer is running Connection must be established each time you log on. Slow but inexpensive

Copyright 2006 Jim Martin22 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.

Copyright 2006 Jim Martin23 Broadband Access: WiMAX WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 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.

Copyright 2006 Jim Martin24 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).