2: Application Layer 1

Socket programming

Socket APIExplicitly created, used, released by apps Client/server paradigm Two types of transport service via socket API:

unreliable datagram reliable, byte stream-oriented

an application-created, application-created, OS-controlledOS-controlled interface (a “door”) into which

application process can both send and both send and receivereceive messages to/from another application

process over the network

socket

2: Application Layer 2

Socket-programming using TCP

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

2: Application Layer 3

Socket programming usingTCPClient must contact server

Server process must be runningServer must have created socket (door) that welcomes client’s contact

Client contacts server by:Creating a TCP socketSpecifying IP address, port number of server processEstablish connection to server TCP (in Java this is done automatically when you create a socket, in C you must explicitly do it)

When contacted by client, server creates new server creates new socketsocket for server process to communicate with client

Allows server to talk with multiple clientsSource port numbers used to distinguish clients

2: Application Layer 4

Stream jargon

A streamstream is a sequence of characters that flow into or out of a process.An input streaminput stream is attached to some input source for the process, e.g., keyboard or socket.An output streamoutput stream is attached to an output source, e.g., monitor or socket.

2: Application Layer 5

Socket programming with TCP

Example client-server app:

1) client reads line from standard input (inFromUser stream) , sends to server via socket (outToServer stream)

2) server reads line from socket3) server converts line to

uppercase, sends back to client

4) client reads, prints modified line from socket (inFromServer stream)

outT

oSer

ver

to network from network

inFr

omS

erve

r

inFr

omU

ser

keyboard monitor

Process

clientSocket

inputstream

inputstream

outputstream

TCPsocket

Clientprocess

client TCP socket

2: Application Layer 6

Client/server interaction: TCP

wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()

create socket,port=x, forincoming request:welcomeSocket =

ServerSocket()

create socket,connect to hostid, port=xclientSocket =

Socket()

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

Server (running on hostid) Client

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

TCP connection setup

2: Application Layer 7

Example: Java client (TCP)

import java.io.*; import java.net.*; class TCPClient {

public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence;

BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));

Socket clientSocket = new Socket("hostname", 6789);

DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());

Createinput stream

Create client socket,

connect to server

Createoutput stream

attached to socket

2: Application Layer 8

Example: Java client (TCP)

BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

sentence = inFromUser.readLine();

outToServer.writeBytes(sentence + '\n');

modifiedSentence = inFromServer.readLine();

System.out.println("FROM SERVER: " + modifiedSentence);

clientSocket.close(); } }

Createinput stream

attached to socket

Send lineto server

Read linefrom server

2: Application Layer 9

Example: Java server (TCP)import java.io.*; import java.net.*;

class TCPServer {

public static void main(String argv[]) throws Exception { String clientSentence; String capitalizedSentence;

ServerSocket welcomeSocket = new ServerSocket(6789); while(true) { Socket connectionSocket = welcomeSocket.accept();

BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));

Createwelcoming socket

at port 6789

Wait, on welcomingsocket for contact

by clientCreate input

stream, attached to socket

2: Application Layer 10

Example: Java server (TCP)

DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

clientSentence = inFromClient.readLine();

capitalizedSentence = clientSentence.toUpperCase() + '\n';

outToClient.writeBytes(capitalizedSentence); } } }

Read in linefrom socket

Create outputstream,

attached to socket

Write out lineto socket

End of while loop,loop back and wait foranother client connection

2: Application Layer 11

Socket-programming using UDP

process

UDP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

UDP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

2: Application Layer 12

Socket programming with 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

2: Application Layer 13

Client/server interaction: UDP

closeclientSocket

Server (running on hostid)

read reply fromclientSocket

create socket,clientSocket = DatagramSocket()

Client

Create, address (hostid, port=x,send datagram request using clientSocket

create socket,port=x, forincoming request:serverSocket = DatagramSocket()

read request fromserverSocket

write reply toserverSocketspecifying clienthost address,port number

2: Application Layer 14

Example: Java client (UDP)

sendP

ack

et

to network from network

rece

iveP

ack

et

inF

rom

Use

r

keyboard monitor

Process

clientSocket

UDPpacket

inputstream

UDPpacket

UDPsocket

Output: sends packet (recallthat TCP sent “byte stream”)

Input: receives packet (recall thatTCP received “byte stream”)

Clientprocess

client UDP socket

2: Application Layer 15

Example: Java client (UDP)import java.io.*; import java.net.*; class UDPClient { public static void main(String args[]) throws Exception { BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); DatagramSocket clientSocket = new DatagramSocket(); InetAddress IPAddress = InetAddress.getByName("hostname"); byte[] sendData = new byte[1024]; byte[] receiveData = new byte[1024]; String sentence = inFromUser.readLine(); sendData = sentence.getBytes();

Createinput stream

Create client socket

Translate hostname to IP

address using DNS

2: Application Layer 16

Example: Java client (UDP)

DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length,

IPAddress, 6789); clientSocket.send(sendPacket); DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); clientSocket.receive(receivePacket); String modifiedSentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedSentence); clientSocket.close(); } }

Create datagram with data-to-send,

length, IP addr, port

Send datagramto server

Read datagramfrom server

2: Application Layer 17

Example: Java server (UDP)import java.io.*; import java.net.*; class UDPServer { public static void main(String args[]) throws Exception { DatagramSocket serverSocket = new DatagramSocket(6789); byte[] receiveData = new byte[1024]; byte[] sendData = new byte[1024]; while(true) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); serverSocket.receive(receivePacket);

Createdatagram socket

at port 6789

Create space forreceived datagram

Receivedatagra

m

2: Application Layer 18

Example: Java server (UDP) String sentence = new String(receivePacket.getData()); InetAddress IPAddress = receivePacket.getAddress(); int port = receivePacket.getPort(); String capitalizedSentence = sentence.toUpperCase();

sendData = capitalizedSentence.getBytes(); DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port); serverSocket.send(sendPacket); } } }

Get IP addrport #, of

sender

Write out datagramto socket

End of while loop,loop back and wait foranother datagram

Create datagramto send to client