Class Notes #1 (08/21 – 08/25)

Lecture of 08/21

CS422 Computer Networks

Home Page – http://www.cs.purdue.edu/homes/cs422

Mailing List (From your CS account):

> mailer add me to cs422l1 <or cs422l2>, etc.

Grading:

– 5% Quizzes

– 5% Homework problems

– 50% Laboratory problems

– 40% Examinations (midterm and final)

Textbook:

Comer, Computer Networks And Internets, second edition, Prentice-Hall, 1999.

Lab: REC108

Schedule: Divided in four parts.

1. Low level details

- Signals and Media

- Digital VS Analog

- Synchronous & Asynchronous

- Modulation and Modems

- Time & Frequency division multiplexing

2. Packet transmission

- Frames & encapsulation

- Error detection techniques

- LAN/WAN topologies

- Bus topology: CSMA/CD, CSMA/CA

- Ethernet

- FDDI, ATM, ADSI

- Repeaters, bridges, Switches

3. Internet working:

- Protocol layering

- IP addressing

- TCP, UDP, ICMP

- IP fragmentation & reassembly

- ARP

- TCP reliability, flow control, port multiplexing

4. Applications:

- Socket API

- Client/server concurrency

- Telnet, FTP, HTML/HTTP, CGI

- RPC, CORBA, DCOM, JAVA RMI

Lecture of 08/23

Lab Configuration:

>ifconfig –a;

Gives IP address of a computer.

What is a network?

- A group of interconnected computers

Why a network is necessary?

¨ Resource sharing

· Files

· Information

· Databases

· Devices, such as printers, etc

· Processing power

¨ Communication between users and applications

- PCs started as autonomous units now the connection to the Internet has become important part of the

computer

" The network is the computer!" ã Sun Microsystems, Inc. 1980s

History of the Internet:

- In the late 1960s the Department of Defense Advanced Research Project Agency (ARPA) created

network nationwide to give computer access to different research centers.

- The alternative was to give a computer to each center. This was too expensive.

- Research in the Internet evolved in 70s and 80s (TCP/IP, FTP, Telnet).

- The Internet becomes a commercial success in the 90s.

- The Internet has been doubling in size every nine to twelve months.

Lecture of 08/25:

Transmission Media:

Forms of energy used for transmission

- Electricity

- Light

- Microwaves

- Sound

- Infrared light

Media used for transmission:

¨Copper wire

· Coaxial cable (Less noise than twisted pair)

· Twisted pair

· Transmission speed is 0.7c (c is speed of light – 3*10⁸ m/s)

· Not good for long distances

- Noise is added

- Signal decreases due to resistance of cable

¨ Fiber optic

· Less susceptible to noise

· Good for long distances

· Expensive

· High bandwidth – high throughput

¨ Radio

· Wireless networks

· Radios are electromagnetic waves also called radio frequency

· Frequency spectrum is limited

- Microwaves also used to link to points. Needs a clear path.

- Satellites

Two types:

- GEO (Geostationary Earth Orbit)

· Remain at the same point in the sky related to earth

· They are about 36,000km (20,000 miles) above earth

· Long delay

· They have to be in the equator

· Limited to 40 – 45 satellites

- LEO (Low Earth Orbit) - -

· Not in equator

· 200 – 400 miles above earth

· Faster than rotation of earth (1.5 hours/revolution)

· An array of satellites is needed

Important limits of a transmission system

- Propagation delay

Time required for a signal to travel across media:

Light: c=3*10⁸ m/s

Copper: 0.7c

- Bandwidth:

Maximum times/sec that a signal can change. This limits the maximum throughput.

Types of Encoding:

- Analog:

Change of the signal is proportion to the information sent.

It is difficult to distinguish noise from information.

- Digital:

Signal is encoded in 0s and 1s. It is possible to differentiate noise from information.

Analog Signal:

Information:

Standards:

ITU – International Telecommunication Union

EIA – Electronic Industries Association

IEEE – Institute of Electrical and Electronic Engineers