1 Computer Networks DA2402

2 Chapter 1-3 Introduction

3 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.

4 You Will Learn  Terminology  Communication basics  Media and signals  Asynchronous and synchronous communication  Relationships among bandwidth, throughput, and noise  Frequency-division and time-division multiplexing

5 You Will Learn (continued)  Networking and network technologies  Packet switching  Framing, parity, and error detection  Local and wide area technologies  Network addressing  Connection and extension (repeaters, bridges, hubs, switches)  Topologies and wiring (star, ring, bus)  Next-hop forwarding  Shortest path computation  Measures of delay and throughput  Protocol layers

6 You Will Learn (continued)  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

7 You Will Learn (continued)  Network applications  Client-server paradigm  Domain name system (DNS)  File transfer (FTP)  Remote login (TELNET)  transfer (SMTP)

8 What You Will NOT Learn  Commercial aspects  Products  Vendors  Prices  Network operating systems  How to purchase/configure/operate

9 Background Required  Ability to program (in Java)  Familiarity with basic tools  Text editor  Compiler / linker / loader

10 Background Required (continued)  Basic knowledge of operating systems  Terminology  Functionality  Processes and concurrent processing  Desire to learn

11 Motivation for Networking  Information access  Interaction among cooperative application programs  Resource sharing

12 Practical Results   File transfer / access  Web browsing  Remote login / execution  The Internet

13 What a Network Includes  Transmission hardware  Special-purpose hardware devices  Interconnect transmission media  Control transmission  Run protocol software  Protocol software  Encodes and formats data  Detects and corrects problems

14 What a Network Does  Provides communication that is  Reliable  Fair  Efficient  From one application to another

15 What a Network Does (continued)  Automatically detects and corrects  Data corruption  Data loss  Duplication  Out-of-order delivery  Automatically finds optimal path from source to destination

16 Network Programming  Network allows arbitrary applications to communicate  Programmer does not need to understand network technologies  Network facilities are accessed through an Application Program Interface

17 Basic Paradigm for Internet Communication  Establish contact  Exchange data (bi-directional)  Terminate contact

18 Establishing Contact  Performed by pair of applications  One application waits for contact (called server )  Other application initiates contact (called client )

19 Identifying a Waiting Application  Conceptually two items specified  Computer  Application on that computer  Terminology  Computer identified by domain name  Application identified by program name

20 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

21 Example API

22 Example #1: Echo  Useful for network testing  Server returns exact copy of data sent  User on computer X runs echoserver  User on another computer runs echoclient X 22000

23 Example #2: Chat  Miniature version of Internet chat service  Allows two users to communicate  User on computer X runs chatserver  User on another computer runs chatclient X 25000

24 Example Application: Web Server  User on computer X runs webserver  User on another computer runs browser and enters URL:

25 Example Code Using API: Echoserver

26 Echoserver (2 of 2)  Actually works on the Internet  API calls replace conventional I/O  No networking knowledge required

27 Example Code Using API: Webserver

28 Webserver (2 of 6)

29 Webserver (3 of 6)

30 Webserver (4 of 6)

31 Webserver (5 of 6)

32 Webserver (6 of 6)

33 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

34 Summary (continued)  Computer networks  Deliver data from source to destination  Automatically find optimal paths  Handle problems that occur  We will learn how