Download EEE3080F - PolyU EIE

Application Layer
EEE3080F
Communication Network and System Fundamentals
http://web.uct.ac.za/depts/commnetwork/eee3080
H Anthony Chan; Yang Li
[email protected]; [email protected]
http://web.uct.ac.za/depts/commnetwork/achan.html
Department of Electrical Engineering
University of Cape Town
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 1 February 23, 2007
♦ Our goals:
♦ conceptual, implementation
aspects of network
application protocols
¾ client-server paradigm
¾ service models
♦ learn about protocols by
examining popular
application-level protocols
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
Application layer
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 2 February 23, 2007
Socket
♦ Principles of network applications
♦ Web and HTTP
♦ FTP
♦ Electronic Mail: SMTP, POP3, IMAP
♦ Ssh
♦ DNS
♦ Port numbers
♦ P2P file sharing
♦ Socket programming with TCP
♦ Socket programming with UDP
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
♦ More chapter goals
♦ specific protocols:
¾ http
¾ ftp
¾ smtp
¾ pop
¾ dns
♦ programming network
applications
¾ socket API
♦ a host-local, application-created/owned, OScontrolled interface (a “door”)
♦ into which application process can both send and
receive messages
♦ to/from another (remote or local) application
process
Communication Networks
218 Page 3 February 23, 2007
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 4 February 23, 2007
Socket programming
Socket-programming using TCP
Goal: learn how to build client/server application that
communicate using sockets
Socket API
♦ introduced in BSD4.1 UNIX, 1981
♦ explicitly created, used, released by apps
♦ client/server paradigm
♦ two types of transport service via socket API:
¾unreliable datagram
¾reliable, byte stream-oriented
♦ Socket: a door between application process and
end-end-transport protocol (UCP or TCP)
♦ TCP service: reliable transfer of bytes from one
process to another
controlled by
application
developer
controlled by
operating
system
process
process
socket
TCP with
buffers,
variables
socket
TCP with
buffers,
variables
host or
server
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 5 February 23, 2007
Socket programming with TCP
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
controlled by
operating
system
host or
server
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 6 February 23, 2007
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 client-local TCP socket
♦ specifying IP address, port number of server
process
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
internet
controlled by
application
developer
Communication Networks
218 Page 7 February 23, 2007
♦ 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
client
¾allows server to talk with multiple clients
♦ application viewpoint
♦ TCP provides reliable, in-order transfer of bytes
(“pipe”) between client and server
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 8 February 23, 2007
Socket programming with TCP
Example client-server app
Socket programming with TCP
Output
stream
to network
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
outToServer
output
stream:
sequence of
bytes
out of
process
Client
Process
inFromServer
Input
stream
monitor
inFromUser
keyboard
Input
stream:
sequence of
bytes
into process
Input
stream
♦ client reads line from standard input (inFromUser
stream) , sends to server via socket (outToServer
stream)
♦ server reads line from socket
♦ server converts line to uppercase, sends back to
client
♦ client reads, prints modified line from socket
(inFromServer stream)
clientSocket TCP socket
from network
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 9 February 23, 2007
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
Client/server socket interaction: TCP
Server (running on hostid)
Client
wait for incoming
connection request
connectionSocket = welcomeSocket.accept()
write reply to
connectionSocket
read reply from
clientSocket
close
connectionSocket
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
close
clientSocket
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Example: Java client (TCP)
public static void main(String argv[]) throws Exception
{
String sentence;
String modifiedSentence;
create socket,
connect to hostid, port=x
clientSocket = Socket()
send request using
clientSocket
read request from
connectionSocket
Communication Networks
218 Page 10 February 23, 2007
import java.io.*;
import java.net.*;
class TCPClient {
create socket,
port=x, for incoming request:
welcomeSocket = ServerSocket()
TCP
connection setup
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 11 February 23, 2007
Create
input stream
Create
client socket,
connect to server
Create
output stream
attached to socket
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("hostname", 6789);
DataOutputStream outToServer =
new DataOutputStream(clientSocket.getOutputStream());
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 12 February 23, 2007
Example: Java client (TCP), cont.
Create BufferedReader inFromServer =
input stream new BufferedReader(new
attached to socket InputStreamReader(clientSocket.getInputStream()));
outToServer.writeBytes(sentence + '\n');
Read line
from server
import java.io.*;
import java.net.*;
class TCPServer {
public static void main(String argv[]) throws Exception
{
String clientSentence;
String capitalizedSentence;
sentence = inFromUser.readLine();
Send line
to server
Example: Java server (TCP)
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
Create
welcoming socket ServerSocket welcomeSocket = new ServerSocket(6789);
at port 6789
while(true) {
Wait, on welcoming
socket for contact Socket connectionSocket = welcomeSocket.accept();
by client
Create input BufferedReader inFromClient =
stream, attached
new BufferedReader(new
to socket
clientSocket.close();
}
}
InputStreamReader(connectionSocket.getInputStream()));
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 13 February 23, 2007
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
Example: Java server (TCP), cont
Create output
stream, attached DataOutputStream outToClient =
to socket new DataOutputStream(connectionSocket.getOutputStream());
Read in line
from socket
clientSentence = inFromClient.readLine();
Write out line
to socket
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence);
}
}
}
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
End of while loop,
loop back and wait for
another client connection
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 15 February 23, 2007
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 14 February 23, 2007
Application layer
♦ Principles of network applications
♦ Web and HTTP
♦ FTP
♦ Electronic Mail: SMTP, POP3, IMAP
♦ Ssh
♦ DNS
♦ Port numbers
♦ P2P file sharing
♦ Socket programming with TCP
♦ Socket programming with UDP
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 16 February 23, 2007
Socket programming with UDP
UDP: no “connection” between client and server
♦ no handshaking
♦ sender explicitly attaches IP address and port of
destination
♦ server must extract IP address, port of sender from
received datagram
UDP: transmitted data may be received out of order,
or lost
application viewpoint
♦ UDP provides unreliable transfer of groups of bytes
(“datagrams”) between client and server
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 17 February 23, 2007
Example: Java client (UDP)
Client
Process
UDP
packet
UDP
packet
create socket,
clientSocket = DatagramSocket()
serverSocket = DatagramSocket()
Create, address (hostid, port=x,
send datagram request
using clientSocket
read request from
serverSocket
write reply to
serverSocket
specifying client host address,
port number
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
read reply from
clientSocket
close
clientSocket
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 18 February 23, 2007
Example: Java client (UDP)
Input:
receives
packet
(TCP
received
“byte
stream”)
Create
input stream
class UDPClient {
public static void main(String args[]) throws Exception
{
Create
client socket
Translate
hostname to IP
address using DNS
Client UDP Socket
to network
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
create socket,
port=x, for incoming request:
import java.io.*;
import java.net.*;
receivePacket
Output:
sends
packet
(TCP
sent
“byte
stream”)
sendPacket
Input
stream
Client
Server (running on hostid)
monitor
inFromUser
keyboard
Client/server socket interaction: UDP
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
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();
from network
Communication Networks
218 Page 19 February 23, 2007
sendData = sentence.getBytes();
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 20 February 23, 2007
Example: Java client (UDP), cont.
Create datagram with
data-to-send,
length, IP addr, port
Example: Java server (UDP)
import java.io.*;
import java.net.*;
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
Send datagram
to server
clientSocket.send(sendPacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
Read datagram
from server
Create
datagram socket
at port 9876
clientSocket.receive(receivePacket);
while(true)
{
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}
Create space for
received datagram
Receive
datagram
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 21 February 23, 2007
Example: Java server (UDP), cont
String sentence = new String(receivePacket.getData());
Get IP addr
port #, of
sender
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
String modifiedSentence =
new String(receivePacket.getData());
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
class UDPServer {
public static void main(String args[]) throws Exception
{
InetAddress IPAddress = receivePacket.getAddress();
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 22 February 23, 2007
Socket programming: references
C-language tutorial (audio/slides):
♦ “Unix Network Programming” (J. Kurose),
♦ http://manic.cs.umass.edu/~amldemo/courseware/intro.
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
Create datagram
to send to client
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
Write out
datagram
to socket
serverSocket.send(sendPacket);
}
}
}
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
Java-tutorials:
♦ “All About Sockets” (Sun tutorial),
http://www.javaworld.com/javaworld/jw-12-1996/jw-12sockets.html
♦ “Socket Programming in Java: a tutorial,”
http://www.javaworld.com/javaworld/jw-12-1996/jw-12sockets.html
End of while loop,
loop back and wait for
another datagram
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 23 February 23, 2007
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 24 February 23, 2007
Application Layer: Summary
Our study of network apps now complete!
♦ application service
requirements:
¾ reliability, bandwidth,
delay
♦ client-server paradigm
♦ Internet transport service
model
¾ connection-oriented,
reliable: TCP
¾ unreliable, datagrams:
UDP
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
♦ specific protocols:
¾ http
¾ ftp
¾ smtp, pop3
¾ ssh
¾ dns
♦ socket programming
¾ client/server
implementation
¾ using tcp, udp sockets
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 25 February 23, 2007
EEE3080F
Communication Network and System Fundamentals
We can do no great things; only small things with
great love. (Mother Teresa of Calcutta)
© 2003-2007
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 27 February 23, 2007
Application Layer: Summary
Most importantly: learned about protocols
♦ typical request/reply
message exchange:
¾ client requests info or
service
¾ server responds with
data, status code
♦ message formats:
¾ headers: fields giving
info about data
¾ data: info being
communicated
What I have is only borrowed from God so
that I may serve others. H Anthony Chan
♦ control vs. data msgs
¾ in-band, out-of-band
♦ centralized vs.
decentralized
♦ stateless vs. stateful
♦ reliable vs. unreliable msg
transfer
♦ “complexity at network
edge”
♦ security: authentication
We can do no great things; only small things with great love.
(Mother Teresa of Calcutta)
Communication Networks
218 Page 26 February 23, 2007