1. Network Programming Eddie Aronovich mail: eddiea@mta.ac.il

2. How did it started ?

3. How can we write communication ? • Application Program Interface (API) • Sockets • TLI (Transport Layer Interface) • System calls • Library functions

4. What is it for ? Communication systems provides 3 services: • Information & resource Sharing • Distance gapping • Backup abilities

5. Fundamentals • Server - An entity which gives services • Client - An entity which requests services • Transport layer - To transfer the data

6. The 7 layers model

7. The 7 Layer model in real life

8. The message is built in one side...

9. And striped in the dest. side…

10. From Lynx to Netscapeor chat client Presentation

12. Descriptors • Everything in Unix is a file • Descriptor is an index into an array

13. Memory Buffers • Contains Socket Address Structure • Headers • Data

14. The Basics of communication LectureII

15. Processing Techniques Decentralized Centralized WEB

16. The Client  Server Model • The server roles: • Give service as asked • Wait the client to appeal to him • The client roles: • Start the communication process • Asks the wanted service

17. Design considerations • Serve single or multiple users • Use reliable or unreliable protocol • Software updates

18. Client and server roles in UDP • Server roles: • Bind a port • Wait for a message to come • Send reply • Client roles: • Send a message • Get the reply

19. User Datagram Protocol* • Simple protocol • Connectionless • Unreliable *{RFC 768}

20. Socket:={ip_addr, port number} • API, an interface for the program to contact with communication. • Enable usage of regular file commands as read, write and so on. • The sockets are structures passed from kernel to process and vice versa.

21. What the socket struct contains ? • Socket type {stream, dgram, raw,…} • Socket options {broadcast, OOB...} • Time to linger wait before close the socket • Socket state flags • Protocol Control Block • Protocol Handle

22. The socket & address structs • Generalstruct sockaddr { uint8_t sa_len; /*Len of socket struct */ sa_family_t sa_family; /*Addr family as AF_INET */ char sa_data[20]; /*Protocol Address */ • IP V4 address socket struct sockaddr_in { uint8_t sin_len; /*The socket length */ sa_family_t sin_family; /*AF_INET for IP addresses */ unit16_t sin_port; /*The port id 16-bit port num */ struct in_addr sin_addr; /*The IP address 32-bit */ char sin_zero [8]; /* FFU - Must be zero */

23. How the socket is created • The system call passes identifiers for address family(e.g.AF_UNIX, AF_INET,etc.), socket type and protocol. • Socket data structure is allocated. • Pointer from the fd table to other i-node struct which points to the socket.

24. User Datagram Protocol (rfc 768) • Data transport layer protocol(Fragment packets to fit local MTU) • Used to make available datagram packet switched mode • Connectionless protocol • Used when RTT is important or no connection needed

25. UDP header

26. UDP by network monitor

27. Lets do it in UDP - client C:\TEMP\udp-cli-c.htm C:\TEMP\udp-cli-c.htm

28. Lets do it in UDP - server C:\TEMP\udp-srv-c.html

29. TCP LectureIII

30. Transmission Control Protocolrfc 793 • Reliability • Sequenced data transfer • Flow control • Full duplex

31. TCP Header

34. Ack & Flow control • Acknowledgements are sent by byte. • The acks can be sent for group of packets (but should arrive before time out of first packet). • Window size is used for flow control and is controlled by receiver.

35. How connection starts ? SYN j SYN k, ACK j+1 ACK k+1 Connection Established

36. How we do it in C ?

37. Ending Sessions Passive close (FIN arrives) Vs. Active close FIN M ACK M+1 FIN N ACK N+1

38. Internet Protocol LectureIV

39. Network Layer • Passing packet from source host to destination host (cross networks if needed) • Independent of the datalink layer • QoS • Flow control

40. Internet Protocol • Connectionless • Unreliable • Best effort

41. Address • IP address consist 32bit and is divided into {network id.,host id} • Part of host id can be used for subnet mask • Some special addresses are defined (as: net-addr, broadcast-addr, multicast-addr)

42. Addresses and Classes Class A Addresses: 0-127.X.X.X Class B Addresses: 128-191.0-255.X.X Class C Addresses: 192-223.0-255.0-255.X

43. Masks • Mask is used to refine network division. • ‘1’b in mask symbolize bit belongs to network address. • ‘0’b in mask symbolize bit belongs to host address.

44. Address conventions • Network address filled with ‘0’ in host address. • Broadcast address filled with ‘1’ in host address. • First, last subnet and address aren’t used

45. How routing is done ? • The router compares destination IP with each Network & subnet address. • Unknown destination is routed to default. • Routers update each other with appropriate algorithms.