Introduction to Network Programming Asst. Prof. Chaiporn Jaikaeo, - PowerPoint PPT Presentation

Introduction to Network Programming Asst. Prof. Chaiporn Jaikaeo, Ph.D. chaiporn.j@ku.ac.th http://www.cpe.ku.ac.th/~cpj Computer Engineering Department Kasetsart University, Bangkok, Thailand

Outline  End-to-end communication  Direct serial communication  Internet communication  Simple client-server applications 2

End-to-End Communication  Direct communication  Communicating devices are directly connected TX TX RX RX GND GND  Internet communication  Communication is performed over the Internet Internet 3

Client-Server Paradigm Client Server  Client  Initiates communication  Issues command  Server  Awaits and respond to commands  Most common model for Internet applications 4

Our Simple Protocol command response Client Server Request Issued by Response by Server Client Your student ID, followed by \r\n id\r\n Your name, followed by \r\n name\r\n Server responds with "ERROR" when receiving an unknown command. 5

Hands-on Activity 1: Serial Comm.  Most basic form of device-to-device communication  However, most recent computers do not come with a serial port  Use USB-Serial dongle instead TX TX RX RX GND GND USB- USB- Serial Serial Dongle Dongle 6

Python's Serial API  Opening a serial port from serial import Serial ser = Serial("/dev/ttyUSB0")  Sending data with newline characters ser.write('Hello\r\n')  Receiving data (blocking call)  Wait until new line characters are received and return the whole line ser.readline()  Wait until 100 bytes are received ser.read(100) 7

Internet Comm. - App's Viewpoint  Two network applications should interact as if they were directly connected write read App App A B Internet 8

Internet Comm. – Socket API  API for developing applications that perform inter- process communication  most commonly for communications across a computer network  Example functions  listen – used by server to wait for contact from client  connect – used by client to contact server  send – used by either client or server to send data  recv – used by either client or server to receive data  close – close the connection 9 9

Services Provided by Socket API  Connection-oriented, stream-like service  Provides virtual stream-oriented pipe  Data transfer is reliable  No loss, in-order arrival App App A B Internet  Both machines use Transmission Control Protocol (TCP) to transfer data 10

Services Provided by Socket API  Connectionless, datagram service  User must prepare packet of data before sending  Data transfer is NOT reliable  Loss possible, out-of-order arrival possible App App A B Internet  Both machines use User-Datagram Protocol (UDP) to transfer data 11

Port Addressing  IP addresses are used to identify hosts (i.e., machines) on the Internet  Port numbers are used to distinguish different processes running on the same host Proc4 Ports Proc3 Proc2 Proc1 Proc5 A B Internet IP Address 1 IP Address 2 12

Hands-on Activity 2: Internet Comm.  Implement Activity 1 over the Internet using stream-oriented service

TCP Socket: Flow in Python Client Server bind() listen() connect() accept() receive() send() send() recv() close() close() 14

Server: Creating Socket  Create a socket object and bind it to port 12345 on any available network interface Listen on any from socket import * Port 12345 interface listen_sock = socket() listen_sock.bind(('0.0.0.0',12345)) listen_sock.listen(1) # max. of 1 client can wait sock,info = listen_sock.accept() 15

Client: Create Socket  On another machine, create a client socket and connect to the server's IP and port from socket import * sock = socket() server = (" <server's IP> ", 12345) sock.connect(server) 16

Finding Out Your IP Address  Windows – Run ipconfig from a command prompt  MacOS/Linux/Unix – Run ifconfig from a terminal 17

Server: Check Client's IP and Port  The method getpeername() tells us about client's IP address and port number  The method returns a tuple (ip-addr, port) addr,port = sock.getpeername() print "Client is connected from",addr 18

Transferring Data  Use send() and recv() methods to send and receive data, respectively  E.g., specify the max number of  At the server, enter the command bytes to be received msg = sock.recv(1024) The server will block until it receives data  At the client, enter the command sock.send('hello') 19

Closing Connection  Server: sock.close() listen_sock.close()  Client: sock.close() 20

Assignment: Throw me your name  I will be running a server on my machine  For each of you  Create a socket to connect to my machine  Then send a line containing <student id> , <first-last name> , <nickname> , <email>  Server will close connection immediately 21