1. CSCE 515: Computer Network Programming
Wenyuan Xu
Department of Computer Science and Engineering
University of South Carolina

2. CSCE515 – Computer Network Programming – 2008 Fall
Course Goal:
Understand the basic principles of computer networks
Network basic
Basic design principles in network protocols
Internet protocols
Wireless network protocols
Study the programming aspects of computer networks
Socket programming
Inter-process communication
 Understand how network research is done
How to determine what is important
What are the trend
CSCE515 – Computer Network Programming – 2008 Fall

3. CSCE515 – Computer Network Programming – 2008 Fall
Administrative
Course website:
Announcements
Homework Assignments
Lecture Notes
Links to required/recommended readings
How to reach me:
Office Hours: MW 4:00pm-5:00pm or by appointment
Office: SWGN 3A54
Prerequisites: CSCE 311 Operating Systems
CSCE515 – Computer Network Programming – 2008 Fall

4. CSCE515 – Computer Network Programming – 2008 Fall
Textbook
Required:
Unix Network Programming, The Sockets Networking API, Volumes 1, by W Richard Stevens, Bill Fenner, Andrew M. Rudoff, published by Addison-Wesley (UNP)
Optional:
TCP/IP Illustrated Volumes 1, by W. Richard Stevens, published by Addison-Wesley, 1994 (TI).
Java Network Programming, by Merlin Hughes, Michael Shoffner, Derek Hamner, Maria Winslow, Conrad Hughes, published Manning Publications
Mailing list:
CSCE515 – Computer Network Programming – 2008 Fall

5. CSCE515 – Computer Network Programming – 2008 Fall
Tentative topics
OSI and TCP/IP Network models
TCP/IP
Socket programming
The Internet and Internet protocol
Web programming
Other network programming
CSCE515 – Computer Network Programming – 2008 Fall

6. CSCE515 – Computer Network Programming – 2008 Fall
Grading
0% Homework (1-2)
Q&A
50% Computer Projects (4 – three in C, one in Java)
20% Midterm
30% Final: closed book, and comprehensive.
Grading scale:
A : 90 — 100
B+ : 87 — 89
B : 80 — 86
C+ : 77 — 79
C : 70 — 76
D : 60 — 69
F <= 59
CSCE515 – Computer Network Programming – 2008 Fall

7. CSCE515 – Computer Network Programming – 2008 Fall
Homework & projects
Programming Environments
Unix workstation lab.:
1D39 (Sun + Linux)
1D45 (Linux)
All students should have an account on Computer Science and Engineering Department Unix workstations
All grading will be done on CSE Linux!
Submission should be via Drop Box
Make sure you understand how to submit (practice first)!
Directions for submission will be posted on the course home page with the first assignment.
CSCE515 – Computer Network Programming – 2008 Fall

8. CSCE515 – Computer Network Programming – 2008 Fall
Project grading
It is expected that everyone is a good programmer
Comment your code!
Your code should be readable, structured!
25% of the grade depends on the quality of the code.
Is the code easy to understand?
Is it easy to make a small change of the functionality?
Can code handle unexpected input, exceptions?
Programs must come with a makefile
Java programs must come with a shell script that starts them:
Sets CLASSPATH to the right value
Remember that I will try your programs in a directory with a different name than you!
CSCE515 – Computer Network Programming – 2008 Fall

9. CSCE515 – Computer Network Programming – 2008 Fall
Project grading
25% of the grade depends on documentation
Documentations must contain:
Your name and student number
How to use your programs
Which program does what, which parameters are needed, screenshots
A description of your program’s design
Documentations must not contain:
Your code in words
“After spending the whole weekend and today at my girlfriend’s house trying to solve the exercises for the Network Programming course which are due today, I must confess that I did not succeed in solving them all”.
CSCE515 – Computer Network Programming – 2008 Fall

10. CSCE515 – Computer Network Programming – 2008 Fall
Grading
Horner code:
All submitted work should be yours!  
NO sharing of code
Do not copy code from Internet
Discussion is encouraged
CSCE515 – Computer Network Programming – 2008 Fall

11. CSCE515 – Computer Network Programming – 2008 Fall
Policies
Make sure you put your course (CSCE515)  in the subject of the message.
Remember that it is not my emergency if you need help at the last minute. I may check my messages in time to help you make a deadline, but this may not necessarily be the case.
Ask specific question instead of general question.
Bad example: “I don’t know why it does not work?”
In general, I will answer quick questions sooner than one that will take a long time to answer
In general I will monitor and respond to during office hours, but in-person students will take precedence.
CSCE515 – Computer Network Programming – 2008 Fall

12. CSCE515 – Computer Network Programming – 2008 Fall
Your Best Strategy
Come to every lecture
Read articles related to network protocols and network programming
Do not wait till last minute to prepare for exam or work on project
Enjoy the fun!
CSCE515 – Computer Network Programming – 2008 Fall

13. Lectures need your help!
Ask questions
Correct Wenyuan! *Extra credit!
Make suggestions!
Read something interesting and relevant to this course? Announce it in class!
CSCE515 – Computer Network Programming – 2008 Fall

14. Introduction

15. CSCE515 – Computer Network Programming – 2008 Fall
What is network?
The term network can refer to any interconnected group or system.
A computer network is composed of multiple computers connected together using a telecommunication system.
“…communication system for connecting end-systems”
End-systems a.k.a. “hosts”
PCs, workstations
dedicated computers
network components
Interconnection may be any medium capable of communicating information:
Copper wire
Lasers (optical fiber)
Radio /Satellite link
Cable (coax)
Example: Ethernet.
CSCE515 – Computer Network Programming – 2008 Fall

16. CSCE515 – Computer Network Programming – 2008 Fall
Why network?
Sharing resources
Resources become available regardless of the user’s physical location (server based, peer2peer)
Load Sharing/utilization
Jobs processed on least crowed machine
Resource can be shared
High reliability
Alternative source of supply (multiple copies)
Computer as a communication tools
Early computers were highly centralized.
Single point of failure
User has to “go to” the computer.
CSCE515 – Computer Network Programming – 2008 Fall

17. Wide variety of types of networks
Circuit switched
dedicated circuit per call
performance (guaranteed)
call setup required
telephone system
Packet switched:
data sent thru net in discrete “chunks”
user A, B packets share network resources
resources used as needed
store and forward: packets move one hop at a time
The Internet (TCP/IP)
CSCE515 – Computer Network Programming – 2008 Fall

18. CSCE515 – Computer Network Programming – 2008 Fall
What is Internet?
local ISP
What is internet?
Network of networks
What is the Internet?
A global internet based on IP protocol
Internet applications:
File transfer
Newsgroup
File sharing
Resource distribution
World wide web
Video conference
Gaming
regional ISP
company
network
CSCE515 – Computer Network Programming – 2008 Fall

19. CSCE515 – Computer Network Programming – 2008 Fall
Emerging networks
Embedded networks
Every physical object is connected
Open/close your garage via network
Know which milk can is about to expire
Sensor networks
Physical space is instrumented and connected
Detect presence of people in a room and set temperature accordingly
Know exactly how many cars on Route 26
Disposable networks
One time use network
Disaster recovery, smart dust
CSCE515 – Computer Network Programming – 2008 Fall

20. CSCE515 – Computer Network Programming – 2008 Fall
Characteristics
Lots of them (density)
Cheap unreliable elements
Run on batteries
Location becomes a key attribute
Information sensing around users
CSCE515 – Computer Network Programming – 2008 Fall

21. CSCE515 – Computer Network Programming – 2008 Fall
Some terms
LAN
WAN
MAN
CSCE515 – Computer Network Programming – 2008 Fall

22. LAN - Local Area Network
connects computers that are physically close together ( < 1 mile).
high speed
multi-access
Technologies:
Ethernet 10 Mbps, 100Mbps
Token Ring 16 Mbps
FDDI Mbps
CSCE515 – Computer Network Programming – 2008 Fall

23. CSCE515 – Computer Network Programming – 2008 Fall
WAN - Wide Area Network
connects computers that are physically far apart. “long-haul network”.
typically slower than a LAN.
typically less reliable than a LAN.
point-to-point
Technologies:
telephone lines
Satellite communications
CSCE515 – Computer Network Programming – 2008 Fall

24. MAN - Metropolitan Area Network
Larger than a LAN and smaller than a WAN
- example: campus-wide network
- multi-access network
Technologies:
coaxial cable
microwave
CSCE515 – Computer Network Programming – 2008 Fall

25. Network Protocols

26. CSCE515 – Computer Network Programming – 2008 Fall
What’s a protocol?
a human protocol and a computer network protocol:
TCP connection
req. Hi
TCP connection
reply. Hi
Got the
time?
Get
<file>
An agreed upon convention for communication. both endpoints need to understand the protocol.
Protocols must be formally defined and unambiguous! We will study lots of existing protocols and perhaps develop a few of our own.
2:00
time
protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
CSCE515 – Computer Network Programming – 2008 Fall

27. Organization of air travel
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
Although this course is about network programming
(and not about networking in general), an understanding
of a complete network model is essential.
CSCE515 – Computer Network Programming – 2008 Fall

28. Organization of air travel: a different view
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
Layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
CSCE515 – Computer Network Programming – 2008 Fall

29. Distributed implementation of layer functionality
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
Departing airport
arriving airport
intermediate air traffic sites
airplane routing
airplane routing
airplane routing
CSCE515 – Computer Network Programming – 2008 Fall

30. Protocol Stack: ISO OSI Model
Data
Header encapsulation and stripping
Application
Presentation
Session
Transport
Network
Data link
Physical
Data AH
Data AH PH SH
Data AH PH TH SH
Data AH PH NH TH SH
Data AH PH DH DT NH TH SH
Data AH PH DH DT NH TH SH
Data AH PH
ISO: the International Standards Organization
OSI: Open Systems Interconnection Reference Model (1984)
CSCE515 – Computer Network Programming – 2008 Fall

31. Communicating between End Hosts
Application
Presentation
Session
Transport
Network
Data link
Physical
Host
Router
Application Protocol
Presentation Protocol
Session Protocol
Transport Protocol
interface
CSCE515 – Computer Network Programming – 2008 Fall

32. CSCE515 – Computer Network Programming – 2008 Fall
Why layering?
Divide a task into pieces and then solve each piece independently (or nearly so).
Establishing a well defined interface between layers makes porting easier.
Functions of each layer are independent of functions of other layers
Thus each layer is like a module and can be developed independently
Each layer builds on services provided by lower layers
Thus no need to worry about details of lower layers -- transparent to this layer
Major Advantages:
Code Reuse
Eases maintenance, updating of system
CSCE515 – Computer Network Programming – 2008 Fall

33. CSCE515 – Computer Network Programming – 2008 Fall
Programs & Processes
A program is an executable file.
A process or task is an instance of a program that is being executed.
A single program can generate multiple processes.
CSCE515 – Computer Network Programming – 2008 Fall

34. CSCE515 – Computer Network Programming – 2008 Fall
Client - Server
A server is a process - not a machine !
A server waits for a request from a client.
A client is a process that sends a request to an existing server and (usually) waits for a reply.
CSCE515 – Computer Network Programming – 2008 Fall

35. Client - Server Examples
Server returns the time-of-day.
Server returns a document.
Server prints a file for client.
Server does a disk read or write.
Server records a transaction.
CSCE515 – Computer Network Programming – 2008 Fall

36. CSCE515 – Computer Network Programming – 2008 Fall
Sample questions:
Difference?
Subnet, a network, WAN
Protocols vs. interface
CSCE515 – Computer Network Programming – 2008 Fall

37. CSCE515 – Computer Network Programming – 2008 Fall
Assignment & Next time
Reading:
How NOT to go about a programming assignment
TI Ch.1
Next Lecture:
OSI model
Data link layer
CSCE515 – Computer Network Programming – 2008 Fall