ITTC Communication Networksjpgs/courses/intronets/lecture...Lab NET-L2-19 Socket Programming Lab...

Communication NetworksThe University of Kansas EECS 563Introduction to Socket Programming

Trúc Anh N. Nguyễn, Mohammed J.F. Alenazi,Egemen K. Çetinkaya, and James P.G. Sterbenz

Department of Electrical Engineering & Computer Science

Information Technology & Telecommunications Research Center

The University of Kansas

jpgs@eecs.ku.edu

https://www.ittc.ku.edu/~jpgs/courses/nets

07 September 2017 KU EECS 563 – Intro Comm Nets – Socket Prog. Lab NET-L2-2

Socket ProgrammingOutline

L2.1 Motivation and overview

L2.2 Socket programming stages

L2.3 Socket programming examples

L2.4 Socket programming assignment

Socket ProgrammingMotivation and Overview

Motivation and OverviewSocket Programming and Applications

• Also called client/server application development

• Introduced in 4.1 BSD in 1982

• Network application implementations

– standard network application

• based on RFCs

• programs conform rules

• port numbers should be implemented per RFC

– proprietary network application

• they don’t conform RFCs

• code will not interoperate

• don’t use standard RFC well-known port numbers (0-1023)

Motivation and OverviewE2E Application Data Flow and Sockets

• Application process send messages via sockets

• Application process is controlled by the developer

• TL (TCP,UDP) is controlled by the OS

Application

Transport

Socket

Network

Physical

Network

Physical

Application

Transport

Socket

Network

Physical

End host End hostChannel Router Channel

Motivation and OverviewSockets and Processes

• Socket is a method for Inter Process Communication

• Processes are created via client/server programs

• IPC can be done on a single host as well

Client program Server program

Client process Server process

Internet

read/write from/to sockets

End Host 1 End Host 2

Socket ProgrammingSocket Programming Stages

Socket Programming StagesPlanning Phase

1. Developer decides programming language and OS

– Python, C, Java etc. and UNIX, Linux, MS etc.

2. Developer should decide:

– to run the application on TCP

• TCP is connection oriented, reliable byte stream channel

– to run the application on UDP

• UDP is connectionless service, best effort, no guarantee

– skip transport layer to run the application

• for hop nodes: e.g. ICMP

• also called raw sockets

3. Developer implements the code

Socket Programming StagesSocket Programming with TCP

• In order to establish connect. between client & server

• Server process

– has to be ready to respond client’s requests

– server has to have a welcoming socket

• Client process

– creates socket

– specifies the destination

– 3-way handshake occurs

• client invokes server’s welcomeSocket accept() method

• server responds this by creating dedicated connectionSocket

• TCP establishes pipe betw. connectionSocket-clientSocket

Socket Programming StagesConnection-Oriented Flow Diagram

socket()

bind()

listen()

accept()

read()

write()

process request

wait for connection

socket()

connect()

write()

read()

connection establishment

data (request)

data (reply)

server client [Stevens-1990]

Socket Programming StagesSocket Programming with UDP

• Connectionless transport between client & server

– there is no initial handshaking

– unlike TCP client can be started first

• Client attaches destination address to each packet

• Client process– creates clientSocket of type DatagramSocket

– in TCP clientSocket is of type Socket

• Server process– creates serverSocket of type DatagramSocket

– there is no welcomeSocket as in TCP

Socket Programming StagesConnectionless Flow Diagram

socket()

bind()

recvfrom()

sendto()

process request

wait for client datasocket()

bind()

sendto()

recvfrom()

data (request)

data (reply)

server client [Stevens-1990]

Socket ProgrammingSocket Programming Examples

• Simple client-server application using TCP and UDP

– the client sends a message to the server

– the server echoes the message back to the client

– the program is written in Python 2.7.13

Socket Programming ExamplesPython TCP Client

from socket import *

serverIP = '127.0.0.1'serverPort = 5005bufferSize = 1024message = "Hello, World!"

print "TCP server IP address:", serverIPprint "TCP server port number:", serverPortprint "Message to be sent to server:", message

clientSocket = socket(AF_INET, SOCK_STREAM)clientSocket.connect((serverIP, serverPort))clientSocket.send(message)recvMessage = clientSocket.recv(bufferSize)print “Message received from server:", recvMessage

clientSocket.close()

Socket Programming ExamplesPython TCP Server

serverPort = 5005bufferSize = 1024

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()message = connectionSocket.recv(bufferSize)print "Message received from client:", messageconnectionSocket.send(message) # echoconnectionSocket.close()

Socket Programming ExamplesPython UDP Client

serverIP = "127.0.0.1"serverPort = 5005bufferSize = 1024message = "Hello, World!"

print "UDP server IP address:", serverIPprint "UDP server port number:", serverPortprint "Message to be sent to server:", message

clientSocket = socket(AF_INET, # InternetSOCK_DGRAM) # UDP

clientSocket.sendto(message, (serverIP, serverPort))recvMessage, serverAddress = clientSocket.recvfrom(bufferSize)print "Message received from server:", recvMessageclientSocket.close()

Socket Programming ExamplesPython UDP Server

serverPort = 5005bufferSize = 1024

serverSocket = socket(AF_INET, # InternetSOCK_DGRAM) # UDP

serverSocket.bind(('', serverPort))print('The server is ready to receive')

while True:message, clientAddress = serverSocket.recvfrom(1024) print "Message received from client:", messageserverSocket.sendto(message, clientAddress)

Socket ProgrammingLab Report Submission Requirement

Socket Programming AssignmentProgram Output Requirement

• Create an application that will

– convert lowercase letters to uppercase

• e.g. [a…z] to [A…Z]

• the code will not change any special characters

• e.g. &*!

– if the character is in uppercase , the program will not alter it

• Create socket API both for

– reliable-byte stream

– datagram services

• Must take the server address and port from the CLI

Socket Programming AssignmentExample for UDP

• Server side:$ python LastName_UDP_server.py 5050

• Client side:$ python LastName_UDP_server.py 127.0.0.1 5050$ Please enter the statement: eecs563$ Return text from the server: EECS563$ Please enter the statement:

• Program should keep asking user for input

– until forced to exit, e.g ctrl-c

Socket Programming AssignmentQuestions to Answer

• What are example applications using TCP and UDP?

– give two examples for each protocol

– what are the port numbers those applications use?

– use examples from well-known port number range

• In the example:

– why the UDP server needs only one socket, whereas the TCP server needs two sockets?

– if the TCP server needs to support n simultaneous connections, each from a different client host, how many sockets would the TCP server need?

Socket Programming AssignmentExtra Credit

• For client/server programs

– print local and foreign address using functions

• Run client and server programs on different machines

• In the UDP client program on slide 17:

– suppose we add the following line after we create the socket

clientSocket.bind(('', 5432))

– will it become necessary to change the UDP server program on slide 18?

– what are the port numbers for the sockets in the UDP client and UDP server programs?

– what were the port numbers before making this change?

Socket Programming AssignmentSubmission Requirements

• Submit on paper in class or to EECS office

• Your submission should include:

– printout of client program for datagram service

– printout of server program for datagram service

– printout of client program for reliable byte-stream service

– printout of server program for reliable byte-stream service

– screenshots of your test cases

– your answers to additional questions

• and optional extra credit

• Use Python

Socket ProgrammingAcknowledgements

Some material in these foils comes from the textbook supplementary materials:

• Kurose & Ross,Computer Networking:

A Top-Down Approach, 7th ed.

https://media.pearsoncmg.com/bc/abp/cs-resources/products/product.html#product,isbn=0133594149

• Stevens,

UNIX Network Programming

Prentice Hall, 1990

http://www.kohala.com/start/unp.html

Socket ProgrammingAcknowledgements

• Donahoo & Calvert,

TCP/IP Sockets in C: Practical Guide for Programmers, 2nd ed.

http://cs.ecs.baylor.edu/~donahoo/practical/CSockets/

• Donahoo & Calvert,

TCP/IP Sockets in Java: Practical Guide for Programmers, 2nd ed.

Morgan Kaufmann, 2008

http://cs.ecs.baylor.edu/~donahoo/practical/JavaSockets/

• Python.org http://wiki.python.org/moin/TcpCommunication

• Python.org http://wiki.python.org/moin/UdpCommunication

Socket ProgrammingAdditional Reading

Some material in these foils comes from the textbook supplementary materials:

• http://www.cs.utsa.edu/~korkmaz/teaching/cn-resources/programs/capitalize-tcp/

• http://www.cs.utsa.edu/~korkmaz/teaching/cn-resources/programs/capitalize-udp/

• http://gaia.cs.umass.edu/ntu_socket/

• http://beej.us/guide/bgnet/

• http://java.sun.com/docs/books/tutorial/networking/sockets/

• http://www.faqs.org/faqs/unix-faq/socket/

• http://www.iana.org/assignments/port-numbers

• http://docs.freebsd.org/44doc/psd/20.ipctut/paper.pdf

• http://docs.freebsd.org/44doc/psd/21.ipc/paper.pdf

ITTC Communication Networksjpgs/courses/intronets/lecture...Lab NET-L2-19 Socket Programming Lab...

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