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The Basics of communication

The Basics of communication. LectureII. Processing Techniques. Decentralized. Centralized. WEB. 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.

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The Basics of communication

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  1. The Basics of communication LectureII

  2. Processing Techniques Decentralized Centralized WEB

  3. 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

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

  5. 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

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

  7. 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.

  8. 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

  9. 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 */

  10. 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.

  11. 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

  12. UDP header

  13. UDP by network monitor

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

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

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