Socket Programming_theory.ppt
- 1. Socket programming goal: learn how to build client/server applications that communicate using sockets socket: door between application process and end-end-transport protocol Application Layer 2-1 Internet controlled by OS controlled by app developer transport application physical link network process transport application physical link network process socket
- 2. Socket programming Two socket types for two transport services: • UDP: unreliable datagram • TCP: reliable, byte stream-oriented Application Layer 2-2 Application Example: 1. client reads a line of characters (data) from its keyboard and sends data to server 2. server receives the data and converts characters to uppercase 3. server sends modified data to client 4. client receives modified data and displays line on its screen
- 3. Socket programming with UDP UDP: no “connection” between client & server no handshaking before sending data sender explicitly attaches IP destination address and port # to each packet receiver extracts sender IP address and port# from received packet UDP: transmitted data may be lost or received out-of-order Application viewpoint: UDP provides unreliable transfer of groups of bytes (“datagrams”) between client and server Application Layer 2-3
- 4. Client/server socket interaction: UDP close clientSocket read datagram from clientSocket create socket: clientSocket = socket(AF_INET,SOCK_DGRAM) Create datagram with server IP and port=x; send datagram via clientSocket create socket, port= x: serverSocket = socket(AF_INET,SOCK_DGRAM) read datagram from serverSocket write reply to serverSocket specifying client address, port number Application 2-4 server (running on serverIP) client
- 5. Application Layer 2-5 Example app: UDP client from socket import * serverName = ‘hostname’ serverPort = 12000 clientSocket = socket(AF_INET, SOCK_DGRAM) message = raw_input(’Input lowercase sentence:’) clientSocket.sendto(message.encode(), (serverName, serverPort)) modifiedMessage, serverAddress = clientSocket.recvfrom(2048) print modifiedMessage.decode() clientSocket.close() Python UDPClient include Python’s socket library create UDP socket for server get user keyboard input Attach server name, port to message; send into socket print out received string and close socket read reply characters from socket into string
- 6. Application Layer 2-6 Example app: UDP server from socket import * serverPort = 12000 serverSocket = socket(AF_INET, SOCK_DGRAM) serverSocket.bind(('', serverPort)) print (“The server is ready to receive”) while True: message, clientAddress = serverSocket.recvfrom(2048) modifiedMessage = message.decode().upper() serverSocket.sendto(modifiedMessage.encode(), clientAddress) Python UDPServer create UDP socket bind socket to local port number 12000 loop forever Read from UDP socket into message, getting client’s address (client IP and port) send upper case string back to this client
- 7. Socket programming with TCP client must contact server server process must first be running server must have created socket (door) that welcomes client’s contact client contacts server by: Creating TCP socket, specifying IP address, port number of server process when client creates socket: client TCP establishes connection to server TCP when contacted by client, server TCP creates new socket for server process to communicate with that particular client • allows server to talk with multiple clients • source port numbers used to distinguish clients (more in Chap 3) Application Layer 2-7 TCP provides reliable, in-order byte-stream transfer (“pipe”) between client and server application viewpoint:
- 8. Client/server socket interaction: TCP Application Layer 2-8 wait for incoming connection request connectionSocket = serverSocket.accept() create socket, port=x, for incoming request: serverSocket = socket() create socket, connect to hostid, port=x clientSocket = socket() server (running on hostid) client send request using clientSocket read request from connectionSocket write reply to connectionSocket TCP connection setup close connectionSocket read reply from clientSocket close clientSocket
- 9. Application Layer 2-9 Example app: TCP client from socket import * serverName = ’servername’ serverPort = 12000 clientSocket = socket(AF_INET, SOCK_STREAM) clientSocket.connect((serverName,serverPort)) sentence = raw_input(‘Input lowercase sentence:’) clientSocket.send(sentence.encode()) modifiedSentence = clientSocket.recv(1024) print (‘From Server:’, modifiedSentence.decode()) clientSocket.close() Python TCPClient create TCP socket for server, remote port 12000 No need to attach server name, port
- 10. Application Layer 2-10 Example app: TCP server from socket import * serverPort = 12000 serverSocket = socket(AF_INET,SOCK_STREAM) serverSocket.bind((‘’,serverPort)) serverSocket.listen(1) print ‘The server is ready to receive’ while True: connectionSocket, addr = serverSocket.accept() sentence = connectionSocket.recv(1024).decode() capitalizedSentence = sentence.upper() connectionSocket.send(capitalizedSentence. encode()) connectionSocket.close() Python TCPServer create TCP welcoming socket server begins listening for incoming TCP requests loop forever server waits on accept() for incoming requests, new socket created on return read bytes from socket (but not address as in UDP) close connection to this client (but not welcoming socket)