Computer Networks and Internets Term Presentation

1. Computer Networks and Internets Term Presentation ASLIHAN BÜLBÜL 28672442386 19.11.2007-23.11.2007

2. Client/Server Architecture • What are Client and Server? • Characteristics of Clients and Servers • Information Flow between Client and Servers • Communication Paradigm • The important issues about Client Server Communication • Most Commonly Used Server Types • Web Server • E-mail Server • FTP Server • IRC Server • DNS Server • Telnet/SSH Server • DHCP (Dynamic Host Configuration Protocol)

3. What are Client and Server? • What is Client? • What is Server?

4. Client Software Local running.(on PC). Contact initiator. Active contact with one remote server at a time. No need of special hardware or sophisticated OS. For one session execution. Arbitrary application program. Server Software Not local running. Contact expectant. Contact from arbitrary clients, but offering a single service. Need of powerful hardware and sophisticated OS. One service, many clients. Special-purpose program. Characteristics of Client and Servers

5. Information Flow Between Client and Servers • Type of Information flow. • Request-Response Mechanism. • Server behaviors in Request- Response Mechanism. • Client behaviors in Request- Response Mechanism.

6. Communication Paradigm • Establish communication. • Exchange messages. • Terminate communication. • Ex. Video: • http://www.youtube.com/watch?v=ey9HCvTIO70

7. The important issues about Client Server Communication • Client and Server communication protocols. • Working style of Client and Servers. • How can a client find server? • Port Numbers. • How can server’s hardware capacity and internet connection speed can be specified?

8. Most Common Server Types Web Server • Publishing web sites. • Importance of Adjusting connection capacity • In LANs or ISP’s system rooms(colocation). • Web hosting Need of: • 7x24 internet connection • Real and static IP address • Domain name • Port situation (80th TCP port) Examples: Open Source Apache Server on Linux, IIS(Internet Information System) on Windows XP OS, Windows 2000.

9. Most Common Server Types-2 E-Mail Server: • Delivery of e-mail from sender to receiver’s e-mail server. • Saving e-mails and deliver them when user connects. • E-mail sending operation: 1.Connecting to the server. 2.Sending e-mail. 3.Looking receiver address’s domain name by server. (xxx@ddd.com) 4.Delivering the mails according to domain name. (if same domain deliver to own POP3 server, otherwise ask to the DNS server and learn the IP address). 5.Send e-mail with STMP(Simple Mail Transfer Protocol) to the other server. 6.Looking to the user name of this e-mail address and accept this e-mail.

10. Most Common Server Types-3 FTP(File Transfer Protocol) Server: • A program or file transfer from network. • Download links • Connecting to FTP: Web browsers Command line of OSs. FTP Client Programs (cuteFTP, FlashFXP) • Updating web sites. • Remote control of PC. • User types (anonymous and private) and security. • Ex: for Linux, ProFTP, PureFTP for Windows, an FTP Server exists with IIS(Internet Information Server) • Uses TCP 21th port.

11. Most Common Server Types-4 IRC (Internet Relay Chat) Server: • Communication and chat. • Basic client server paradigm. • More than one clients and server at the scene. • Ex: for UNIX/shell: ircII for Windows:mIRC or PIRCH for Macintosh Ircle

12. Most Common Server Types-5 DNS (Domain Name)Server: • Conversion between domain names and IPs. • Resource Records (tables). • Hierarchical communication of DNS servers. • Cache (temporary database) and TTL (time to live). • Duties of DNS • Response to Clients • Response to other DNS servers. • nslookup command. • For client requests UDP 53th port. • For other DNS requests TCP 53th port. • Mostly used DNS server is BIND (Berkeley Internet Domain).

13. Most Common Server Types-6 Telnet/SSH (Secure Shell) Servers: • Remote connection and using commands. (LAN and internet) • Terminal usage. • E-mail send/receive, e-chat, news group in the past, management and control duties now. • Difference of SSH from Telnet. • Text-based servers.

14. DHCP(Dynamic Host Configuration Protocol) • IP address specification. • Distributing IP addresses. • IP address pool. • Net mask, gateway and DNS server addresses.

15. Most Common Server Types

16. PORTS • Definitions and Classification • TCP (Transport Control Protocol) • Characteristics of TCP • UDP (User Datagram Protocol) • TCP/UDP and Application Programs • Port Numbers of various application programs • Packet Loss and Retransmission

17. Definitions and Classification • What is PORT? • Why port is needed? • Entrance points. • Security. • Types of ports • TCP (Transport Control Protocol) • UDP (User Datagram Protocol)

18. TCP (Transport Control Protocol) • Segmentation and TCP • Secure Communication • Advantage and disadvantages of security • Source Port • Destination Port • Connection-Oriented • SYN, SYN/ACK, ACK, FIN • Acknowledgement information • Optimum Window Size (536 byte)

19. Characteristics of TCP • Connection-Orientation • Point-To-Point Communication • Complete Reliability • Full Duplex Communication • Stream Interface • Reliable Connection Startup • Graceful Connection Shutdown

20. UDP (User Datagram Protocol) • Simpler than TCP • No handshaking • Not secure communication • No acknowledgement information • Advantages and disadvantages

21. TCP/UDP and Application Programs • Differences of TCP and UDP • Where to use TCP or UDP? • Simultaneous usage of TCP & UDP • Ex. MSN messenger, Skype • See the open ports: • http://www.youtube.com/watch?v=fuZylN8ZV_o Port Numbers of some network Servers

22. Packet Loss and Retransmission • Acknowledgement message (ACK) • Timer • Delay • Retransmission • Concurrent working of application programs. • Duplicate packets problem

23. IP (Internet Protocols) • General Expression about IP • The explanation of IPv4 • IPv4 address format • The explanation of IPv6 • IPv6 address format • Transition Duration to IPv6 • IPV4 vs. IPv6

24. General Expression about IP • What is IP? The Success of IP: • Unique • Locator • Identifier • Handling heterogeneity • IP datagram • Compatibility • Frame sizes and IP

25. IPv4 • IP and IPv4 • 32 bit address • Solving need of IP • NAT (Network Address Translation), CIDR(Classless Inter-Domain Routing), DHCP • What will happen in 2010s? Deficiencies of IPv4 • Quality of service • Security • Compatibility with electronic devices • IPv4 Routing Protocols

26. IPv4 Address Format • Four numbers, each ranging from 0 to 255 Ex. 147.132.42.18 • Classes of networks • A class (1-126) • B class (128-191) • C class (192-223)

27. IPv6 • Why IPv6 is needed? • Transition from IPv4 to IPv6 • Changes in this transition duration • Producers and IPv6 (MAC OS, Solaris, Linux, WinXP/2003) • Providing IPv6 support to application programs • IOS (Interface Operating Systems) Nokia, Cisco,3Com • Ex. video: http://www.youtube.com/watch?v=qsWNWm2O0_Q

28. IPv6 Address Format • 8 Pieces, 32 x hexadecimal numbers 32*4=128 bits. Ex: 3FFE:0B00:0000:0000:0000:0000:0000:0046 • 0000:0000:0000:0000:0000:0000:0000:0000 Same with  0:0:0:0:0:0:0:0 or :: • 2010:0234:0000:0000:0067:0000:0000:00E2 Same with  2010:234:0:0:67:E2 • 40A1:0000:16FE:0000:0000:0C23:86E1 Same with  40A1:0:16FE:0:0:C23:86E1 Or 40A1:0:16FE::C23:86E1 Only once usage of ::

29. Transition Duration to IPv6 • Changes in Client-Server Software • Cost of change • Updating; • Client programs, • OSs, • Hardware • Network Connection device software updates.

30. IPv4 vs. IPv6 Ex. video: http://www.youtube.com/watch?v=-ZW8v0zd6C0

31. Sources BOOKS: • Bilgisayar Ağları ve Güvenliği – Alper ÖZBİLEN (Pusula Yayıncılık) • IPv6 clearly explained- Pete LOSHIN • Internetworking with TCP/IP vol:III Client Server Programming and Applications INTERNET Sources: • http://en.wikipedia.org/wiki/IP_address • www.youtube.com (videos)

32. Thank you for listening. Questions