1. CSI 4118 – UNIVERSITY OF OTTAWA
Introduction
Computer Networks & Protocols
Dr. R.L. Probert, SITE, University of Ottawa
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CSI 4118 – UNIVERSITY OF OTTAWA

2. CSI 4118 – UNIVERSITY OF OTTAWA
Part I
Introduction
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CSI 4118 – UNIVERSITY OF OTTAWA

3. CSI 4118 – UNIVERSITY OF OTTAWA
Topic and Scope
Computer networks and internets: an overview of concepts, terminology, and technologies that form the basis for digital communication in private corporate networks and the global Internet.
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CSI 4118 – UNIVERSITY OF OTTAWA

4. CSI 4118 – UNIVERSITY OF OTTAWA
You Will Learn
Internets and Internetworking
Motivation and concept
Internet Protocol (IP) datagram format and addressing
Internet routers and routing
Address binding (ARP)
Internet control messages (ICMP)
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
Protocol ports and demultiplexing
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CSI 4118 – UNIVERSITY OF OTTAWA

5. You Will Learn (continued)
Some network applications!
Client-server paradigm
Domain name system (DNS)
File transfer (FTP)
Remote login (TELNET)
transfer (SMTP)
Web technologies and protocols
HTTP, CGI, Java
Security
Voice over IP, …
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CSI 4118 – UNIVERSITY OF OTTAWA

6. CSI 4118 – UNIVERSITY OF OTTAWA
Background Required
Ability to program in Java, ability to read C code
Knowledge of low-level programming constructs
Pointers
Bit fields in structures
Familiarity with basic tools
Text editor
Compiler / linker / loader
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CSI 4118 – UNIVERSITY OF OTTAWA

7. Background Required (continued)
Basic knowledge of operating systems
Terminology
Functionality
Processes and concurrent processing
CSI 3103/3503
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8. Motivation for Networking
Information access
Interaction among cooperative application programs
Resource sharing
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9. CSI 4118 – UNIVERSITY OF OTTAWA
The Internet Concept The illusion of a single network that TCP/IP software provides to users and applications
User’s
computers
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CSI 4118 – UNIVERSITY OF OTTAWA

10. CSI 4118 – UNIVERSITY OF OTTAWA
The Internet Concept The underlying physical structure in which a computer attaches to one physical network and routers interconnect the networks
Net 2
Net 1
Net 1
Net 4
Net 3
Net 5
Router
Physical net
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CSI 4118 – UNIVERSITY OF OTTAWA

11. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.1
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CSI 4118 – UNIVERSITY OF OTTAWA

12. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.2
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13. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.3
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14. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.4
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15. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.5
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16. CSI 4118 – UNIVERSITY OF OTTAWA
Figure 2.6
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17. CSI 4118 – UNIVERSITY OF OTTAWA
Practical Examples
File transfer / access
Web browsing
Remote login / execution
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CSI 4118 – UNIVERSITY OF OTTAWA

18. CSI 4118 – UNIVERSITY OF OTTAWA
What is a Network?
Transmission hardware (media) [Ch. 4]
Special-purpose hardware devices [Ch. 9, 10]
Interconnect transmission media
Control transmission
Run protocol software
Protocol software [Ch. 16 and following]
Encodes and formats data
Detects and corrects problems
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CSI 4118 – UNIVERSITY OF OTTAWA

19. CSI 4118 – UNIVERSITY OF OTTAWA
What does a Network Do?
Provides communication which is:
Reliable
Fair
Efficient [15.14]
Allows communication between applications
(Allows arbitrary applications to communicate via Network (Distributed) Programming)
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CSI 4118 – UNIVERSITY OF OTTAWA

20. CSI 4118 – UNIVERSITY OF OTTAWA
Network Efficiency
Delay
Propagation Delay
Switching Delay
Access Delay
Queuing Delay
Throughput
Rate of Data Transmission
How many bits can enter (or leave) network in fixed unit of time
Effective Throughput
Capacity
Congestion
Degree of Utilization
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CSI 4118 – UNIVERSITY OF OTTAWA

21. What Does a Network Do? (continued)
Automatically detects and corrects
Data corruption (e.g. CRC [7.9, 7.10])
Data loss
Duplication
Out-of-order delivery e.g., sequencing [16.10]
Automatically finds optimal path from source to destination, routing [Ch. 13]
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CSI 4118 – UNIVERSITY OF OTTAWA

22. Network (Distributed) Programming [Ch. 3]
Networks allow arbitrary applications to communicate
Programmer does not need to understand network technologies
Network facilities are accessed through an Application Program Interface (API)
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CSI 4118 – UNIVERSITY OF OTTAWA

23. Basic Paradigm for Pairwise Internet Communication
Establish contact
Exchange data (bi-directional)
Terminate contact
Note: NO data processing by the network
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CSI 4118 – UNIVERSITY OF OTTAWA

24. CSI 4118 – UNIVERSITY OF OTTAWA
Establishing Contact
Performed by pair of applications
One application waits for contact (called server)
Other application initiates contact (called client)
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CSI 4118 – UNIVERSITY OF OTTAWA

25. Identifying a Waiting Application
Conceptually two items specified
Computer
Application on that computer
Terminology
Computer identified by domain name
Application identified by program name
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CSI 4118 – UNIVERSITY OF OTTAWA

26. Representations and Translations
Humans use names such as
computer:
application: ftp
Network protocols require binary values
Library routines exist to translate from names to numbers
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CSI 4118 – UNIVERSITY OF OTTAWA

27. CSI 4118 – UNIVERSITY OF OTTAWA
Example API
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28. CSI 4118 – UNIVERSITY OF OTTAWA
Simplified API
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CSI 4118 – UNIVERSITY OF OTTAWA

29. Simplified API (Cont’d)
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30. Simplified API (Cont’d)
The Await_Contact Function
connection await_contact(appnum a)
The argument specifies a number that identifies the server application
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CSI 4118 – UNIVERSITY OF OTTAWA

31. Simplified API (Cont’d)
The Make_Contact Function
connection make_contact(computer c, appnum a)
The client uses the return value, which is of type connection, to transfer data
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CSI 4118 – UNIVERSITY OF OTTAWA

32. Simplified API (Cont’d)
The appname_to_appnum Function
appnum appname_to appnum(char *a)
Clients and servers both use appname_to_appnum to translate from a human-readable name for a service to an internal binary value
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CSI 4118 – UNIVERSITY OF OTTAWA

33. Simplified API (Cont’d)
The Cname_to_comp Function
computer cname_to_comp(char *c)
Clients call cname_to_comp convert from a human-readable computer name to the internal binary value
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CSI 4118 – UNIVERSITY OF OTTAWA

34. Simplified API (Cont’d)
The Send Function
int send (connection con, char *buffer, int length, int flags)
Both clients and servers use send to transfer data across the network
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CSI 4118 – UNIVERSITY OF OTTAWA

35. Simplified API (Cont’d)
The Recv And Recvln Functions
int recv (connection con, char *buffer, int length, int flags)
Both clients and servers use recv to access data that arrives across the network
int recvln (connection con, char *buffer, int length)
Recvln repeatedly calls recv until an entire line of test has been received
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CSI 4118 – UNIVERSITY OF OTTAWA

36. Simplified API (Cont’d)
The Send_eof Function
int send_eof (connection con)
Both the client and server must use send_eof after sending data to inform the other side that no further transmission will occur
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CSI 4118 – UNIVERSITY OF OTTAWA

37. Simplified API (Cont’d)
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38. CSI 4118 – UNIVERSITY OF OTTAWA
Conceptual Client-Server Map
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39. CSI 4118 – UNIVERSITY OF OTTAWA
Example #1: Echo
Useful for network testing
Server returns exact copy of data sent
User on computer X runs
echoserver 22000
User on another computer runs
echoclient X 22000
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CSI 4118 – UNIVERSITY OF OTTAWA

40. Example Code Using API: Echoserver
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CSI 4118 – UNIVERSITY OF OTTAWA

41. CSI 4118 – UNIVERSITY OF OTTAWA
Echoserver (Cont’d)
Actually works on the Internet
API calls replace conventional I/O
No networking knowledge required
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CSI 4118 – UNIVERSITY OF OTTAWA

42. CSI 4118 – UNIVERSITY OF OTTAWA
Example #2: Chat
Miniature version of Internet chat service
Allows two users to communicate
User on computer X runs
chatserver 25000
User on another computer runs
chatclient X 25000
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CSI 4118 – UNIVERSITY OF OTTAWA

43. Example Application: Web Server
User on computer X runs
webserver 27000
User on another computer runs browser and enters URL:
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CSI 4118 – UNIVERSITY OF OTTAWA

44. Example Code Using API: Webserver
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CSI 4118 – UNIVERSITY OF OTTAWA

45. CSI 4118 – UNIVERSITY OF OTTAWA
Webserver (2 of 6)
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CSI 4118 – UNIVERSITY OF OTTAWA

46. CSI 4118 – UNIVERSITY OF OTTAWA
Webserver (3 of 6)
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CSI 4118 – UNIVERSITY OF OTTAWA

47. CSI 4118 – UNIVERSITY OF OTTAWA
Webserver (4 of 6)
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CSI 4118 – UNIVERSITY OF OTTAWA

48. CSI 4118 – UNIVERSITY OF OTTAWA
Webserver (5 of 6)
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CSI 4118 – UNIVERSITY OF OTTAWA

49. CSI 4118 – UNIVERSITY OF OTTAWA
Webserver (6 of 6)
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CSI 4118 – UNIVERSITY OF OTTAWA

50. Network Programming in Java
The java.net package provides two classes--Socket and ServerSocket--that implement the client side of the connection and the server side of the connection, respectively.
java.io package also has to be used together with socket API.
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CSI 4118 – UNIVERSITY OF OTTAWA

51. Example API in Java (v1.3+)
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52. Example Code Using Java API: (1) EchoServer.java
import java.io.*; import java.net.*; public class EchoServer {     public static void main(String args[]) {
// declare a server socket and a client socket for the server
ServerSocket echoServer = null;
String line;
BufferedReader br;
PrintStream os;
Socket clientSocket = null;
// open a server socket on a specfic port. args[0] is the port number
try {
echoServer = new ServerSocket(Integer.parseInt(args[0]));
} catch (IOException e) { }
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CSI 4118 – UNIVERSITY OF OTTAWA

53. CSI 4118 – UNIVERSITY OF OTTAWA
EchoServer.java (2 of 2)
try {
// open a socket to listen and accept connections from client
clientSocket = echoServer.accept();
br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
os = new PrintStream(clientSocket.getOutputStream());
// once receiving data from client, echo it back to the client.
while (true) {
line = br.readLine();
os.println(line);
} } catch (IOException e) { }
}//EchoServer.java
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CSI 4118 – UNIVERSITY OF OTTAWA

54. CSI 4118 – UNIVERSITY OF OTTAWA
(2) EchoClient.java
import java.io.*;
import java.net.*;
public class EchoClient {
public static void main(String[] args) throws IOException {
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
//open a socket to a specified host and port.
try { // args[0] is host address, args[1] is port number
echoSocket = new Socket(args[0], Integer.parseInt(args[1]));
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader( echoSocket.getInputStream()));
} catch (Exception e) {}
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CSI 4118 – UNIVERSITY OF OTTAWA

55. (2) EchoClient.java (2 of 2)
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String userInput;
//send user's input to server, and retrieve what the server sends back.
while ((userInput = stdIn.readLine()) != null) {
out.println(userInput);
System.out.println("echo: " + in.readLine()); }
//close everything gracefully
out.close();
in.close();
stdIn.close();
echoSocket.close();
}//EchoClient.java
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CSI 4118 – UNIVERSITY OF OTTAWA

56. CSI 4118 – UNIVERSITY OF OTTAWA
(3) Test Run
1. Compile EchoServer.java and EchoClient.java.
2. Start server program:
java EchoServer localhost 4118
3. Start client program:
java EchoClient 4118
Then type in something at prompt to see what will happen.
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CSI 4118 – UNIVERSITY OF OTTAWA

57. CSI 4118 – UNIVERSITY OF OTTAWA
Summary
Studying networks is important because
The world is interconnected
Applications now operate in a distributed environment
This course
Covers networking and internetworking
Explains the mystery
Will be hard work
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CSI 4118 – UNIVERSITY OF OTTAWA

58. CSI 4118 – UNIVERSITY OF OTTAWA
Summary (continued)
Computer networks
Deliver data from source to destination
Automatically find optimal paths
Handle problems that occur
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CSI 4118 – UNIVERSITY OF OTTAWA