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2: Application Layer

Chapter 2 Application Layer. Computer Networking: A Top Down Approach , 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. 2: Application Layer. 1. Chapter 2: Application layer. 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail

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2: Application Layer

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  1. Chapter 2Application Layer Computer Networking: A Top Down Approach, 5th edition. Jim Kurose, Keith RossAddison-Wesley, April 2009. 2: Application Layer 1

  2. Chapter 2: Application layer • 2.1 Principles of network applications • 2.2 Web and HTTP • 2.3 FTP • 2.4 Electronic Mail • SMTP, POP3, IMAP • 2.5 DNS • 2.6 P2P applications • 2.7 Socket programming with TCP • 2.8 Socket programming with UDP 2: Application Layer 2

  3. recv and send • recv may be used instead of read (and is recommended): n = recv(fd, buffer, count, flags); • The first three arguments are the same as for read. The flags argument provides additional flexibility. Interesting flags are MSG_DONTWAIT and MSG_PEEK. Refer to recv(2) for details. 2: Application Layer 3

  4. recv and send • Similarly send may be used instead of write (and is also recommended): n = send(fd, buffer, count, flags); • Interesting flags are MSG_DONTWAIT, MSG_MORE and MSG_DONTROUTE. Refer to send(2) for details. 2: Application Layer 4

  5. Chapter 2: Application layer • 2.1 Principles of network applications • 2.2 Web and HTTP • 2.3 FTP • 2.4 Electronic Mail • SMTP, POP3, IMAP • 2.5 DNS • 2.6 P2P applications • 2.7 Socket programming with TCP • 2.8 Socket programming with UDP 2: Application Layer 5

  6. application viewpoint UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server Socket programming with UDP • UDP: no “connection” between client and server • no handshaking • sender explicitly attaches IP address and port of destination to each packet • server must extract IP address, port of sender from received packet UDP: transmitted data may be received out of order, or lost 2: Application Layer 6

  7. Client create socket, clifd = socket() Create datagram with server IP and port=x; send datagram viasendto read datagram using recvfrom write reply using sendto specifying client address, port number read datagram using recvfrom close close() Client/server socket interaction: UDP Server (running on hostid) create socket, port= x. srvfd = socket() bind() 2: Application Layer 7

  8. UDP Programming • The client functions for passing UDP datagrams are: socket(), sendto(), and recvfrom(). It is not necessary for the client to connect() with the server. (Although connect() can be used.) • The server uses socket(), bind(), recvfrom(), and sendto(). The server does not accept()a connection from the client, instead recvfrom() returns the data and client address. 2: Application Layer 8

  9. UDP Programming • The sendto() routine takes a destination address structure as an argument: typedef struct sockaddr SA; struct sockaddr_in srvaddr_in; memset(&srvaddr_in, 0, sizeof(srvaddr_in)); srvaddr.sin_family = AF_INET; srvaddr.sin_port = htons(9000); inet_pton(AF_INET, “10.10.0.9”, &srvaddr_in.sin_addr.s_addr); sfd = socket(AF_INET, SOCK_DGRAM, 0); sendto(sfd, msg, msglen, 0, (SA *)&srvaddr_in, sizeof(srvaddr_in)); 2: Application Layer 9

  10. UDP Programming • recvfrom() returns an address as an argument. The address is used by the server to respond to the proper client: n = recvfrom(sockfd, mesg, mesg_len, 0, (SA *)&cliaddr_in, &len); sendto(sockfd, mesg, n, 0, (SA *)&cliaddr_in, len); • A NULL address may be used in recvfrom() if we do not care about the address. • Refer to udp_server.cpp for a complete example of UDP socket programming (a modified echo server). • In-class Exercise: Write a udp_client.cpp program to communicate with udp_server.cpp. It should prompt the user for input, send the input to the server, and then read and display the response. 2: Application Layer 10

  11. Chapter 2: Summary our study of network apps now complete! • specific protocols: • HTTP • FTP • SMTP, POP, IMAP • DNS • P2P: BitTorrent, Skype • socket programming • application architectures • client-server • P2P • hybrid • application service requirements: • reliability, bandwidth, delay • Internet transport service model • connection-oriented, reliable: TCP • unreliable, datagrams: UDP 2: Application Layer 11

  12. Chapter 2: Summary Most importantly: learned about protocols • typical request/reply message exchange: • client requests info or service • server responds with data, status code • message formats: • headers: fields giving info about data • data: info being communicated • Important themes: • control vs. data msgs • in-band, out-of-band • centralized vs. decentralized • stateless vs. stateful • reliable vs. unreliable msg transfer • “complexity at network edge” 2: Application Layer 12

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