Class Notes #1 (08/21 – 08/25)
Lecture of 08/21
CS422 Computer Networks
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– 5% Quizzes
– 5% Homework problems
– 50% Laboratory problems
– 40% Examinations (midterm and final)
Comer, Computer Networks And Internets, second edition, Prentice-Hall, 1999.
Schedule: Divided in four parts.
- 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
- FDDI, ATM, ADSI
- Repeaters, bridges, Switches
3. Internet working:
- Protocol layering
- IP addressing
- TCP, UDP, ICMP
- IP fragmentation & reassembly
- TCP reliability, flow control, port multiplexing
- Socket API
- Client/server concurrency
- Telnet, FTP, HTML/HTTP, CGI
- RPC, CORBA, DCOM, JAVA RMI
Lecture of 08/23
Gives IP address of a computer.
What is a network?
- A group of interconnected computers
Why a network is necessary?
¨ Resource sharing
· 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
" 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:
Forms of energy used for transmission
- Infrared light
Media used for transmission:
· 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
· High bandwidth – high throughput
· 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.
- 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
Maximum times/sec that a signal can change. This limits the maximum throughput.
Types of Encoding:
Change of the signal is proportion to the information sent.
It is difficult to distinguish noise from information.
Signal is encoded in 0s and 1s. It is possible to differentiate noise from information.
ITU – International Telecommunication Union
EIA – Electronic Industries Association
IEEE – Institute of Electrical and Electronic Engineers