CSI 4118 – UNIVERSITY OF OTTAWA Introduction Computer Networks & Protocols Dr. R.L. Probert, SITE, University of Ottawa FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Part I Introduction FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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. FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

You Will Learn (continued) Some network applications! Client-server paradigm Domain name system (DNS) File transfer (FTP) Remote login (TELNET) Email transfer (SMTP) Web technologies and protocols HTTP, CGI, Java Security Voice over IP, … FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Background Required (continued) Basic knowledge of operating systems Terminology Functionality Processes and concurrent processing CSI 3103/3503 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Motivation for Networking Information access Interaction among cooperative application programs Resource sharing FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.1 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.2 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.3 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.4 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.5 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Figure 2.6 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Practical Examples E-mail File transfer / access Web browsing Remote login / execution FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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] FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Basic Paradigm for Pairwise Internet Communication Establish contact Exchange data (bi-directional) Terminate contact Note: NO data processing by the network FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Identifying a Waiting Application Conceptually two items specified Computer Application on that computer Terminology Computer identified by domain name Application identified by program name FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Representations and Translations Humans use names such as computer: www.netbook.cs.purdue.edu application: ftp Network protocols require binary values Library routines exist to translate from names to numbers FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Example API FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Simplified API FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Simplified API (Cont’d) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Simplified API (Cont’d) The Await_Contact Function connection await_contact(appnum a) The argument specifies a number that identifies the server application FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Simplified API (Cont’d) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Conceptual Client-Server Map FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Example Code Using API: Echoserver FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Echoserver (Cont’d) Actually works on the Internet API calls replace conventional I/O No networking knowledge required FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Example Application: Web Server User on computer X runs webserver 27000 User on another computer runs browser and enters URL: http://X:27000/index.html FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Example Code Using API: Webserver FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Webserver (2 of 6) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Webserver (3 of 6) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Webserver (4 of 6) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Webserver (5 of 6) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Webserver (6 of 6) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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. FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

Example API in Java (v1.3+) FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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) { } FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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) {} FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

(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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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. FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

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 FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA

CSI 4118 – UNIVERSITY OF OTTAWA Summary (continued) Computer networks Deliver data from source to destination Automatically find optimal paths Handle problems that occur FALL 2003 CSI 4118 – UNIVERSITY OF OTTAWA