1. Transport layer (last part) Application layer
CSE 524: Lecture 14
Transport layer (last part)
Application layer

2. Administrative
Homework #4 due today
Reading assignment Chapter 2

3. Transport layer Done except for TCP Reno fast recovery This class
Finish TCP Reno fast recovery
Start application layer
Socket programming
HTTP

4. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd=8
base 23 22 21 20 19 18 17 16 S D
Ack16
(15)

5. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd=8
base 23 22 21 20 19 18 17 16 X S D

6. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd=8 23 22 21 20 19 18
base S D
Ack16
(17) S D
Ack16
(17)
Ack16
(18)
Ack16
(19)
Ack16
(20)
Ack16
(21)
Ack16
(22)
Ack16
(23) 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd=8
base

7. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
3rd Dup. Ack 13
cwnd=8 S D
base
Ack16
(17)
Ack16
(18)
Ack16
(19)
Ack16
(20)
Ack16
(21)
Ack16
(22)
Ack16
(23) 16 S D
Ack16
(19)
Ack16
(20)
Ack16
(21)
Ack16
(22)
Ack16
(23) 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd_to_use_after_recovery=4
inflated_cwnd=4+3=7
base

8. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24 16
cwnd_to_use_after_recovery=4
inflated_cwnd=8
base S D
Ack16
(20)
Ack16
(21)
Ack16
(22)
Ack16
(23) 24 16 S D
Ack16
(21)
Ack16
(22)
Ack16
(23) 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
cwnd_to_use_after_recovery=4
inflated_cwnd=9
base

9. TL: Reno fast recovery example15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 15 16 17 18 19 20 21 22 23 24
cwnd_to_use_after_recovery=4
inflated_cwnd=12
base 27 26 25 24 S D
Ack24
(16) 27 26 25 24 S D 15 16 17 18 19 20 21 22 23 24 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
cwnd=4
base

10. TL: Reno fast recovery example
What if the retransmission is lost?
Window inflation to support sending at halved rate until eventual RTO
Reference

11. Application layer Network programming Application layer functions
API to transport layer
BSD socket API
java.net API
Application layer functions
Specific application layers
http
ftp
smtp
dns

12. AL: Network programming
How can applications programmatically access TCP/UDP/IP?
Many possible interfaces
Too many to teach adequately in detail
Socket APIs
BSD socket API
Java socket API
Other APIs
Client-side Java URLconnections
Server-side Java servlets
RPC, CORBA, Java RMI (not covered)

13. AL: Socket programming
Socket API
introduced in BSD4.1 UNIX, 1981
explicitly created, used, released by apps
client/server paradigm
three main types of transport service via socket API:
unreliable datagram
reliable, byte stream-oriented
raw IP datagrams
a host-local, application-created/owned,
OS-controlled interface (a “door”) into which
application process can both send and
receive messages to/from another (remote or
local) application process
socket

14. AL: Socket-programming using TCP
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
application
developer
process
TCP with
buffers,
variables
socket
process
TCP with
buffers,
variables
socket
controlled by
operating
system
controlled by
operating
system
internet
host or
server
host or
server

15. AL: 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
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
allows server to talk with multiple clients (using multiple sockets)
TCP provides reliable, in-order
transfer of bytes (“pipe”)
between client and server
application viewpoint

16. AL: BSD sockets in C/Unix
Socket API (socket.h)
socket(): create unnamed socket (data structure)
UDP (SOCK_DGRAM), TCP (SOCK_STREAM)
IP (SOCK_RAW)
bind(): name socket (bind local address to socket)
listen(): enable socket to accept connections
accept(): get connect() request from listen queue, allocate file descriptor for new socket
connect(): initiate connection on a socket (TCP handshake)
send(), sendto(), sendmsg(), writev(), write(): send data
recv(), recvfrom(), recvmsg(), readv(), read(): receive data
setsockopt(), getsockopt(): set socket options (such as buffer sizes, flag fields)
close(), shutdown(): teardown connection

17. AL: BSD sockets in action
UDP example
TCP example
client
server
client
server
socket()
socket()
socket()
bind()
bind()
socket()
bind()
connect()
listen()
sendto()
accept()
recvfrom()
write()
read()
sendto()
write()
recvfrom()
read()

18. AL: BSD example For reference only….

19. AL: Java network programming
Java network applications
java.net package
System-dependent
implementations

20. AL: Java installation on church/state
Programming assignment
J2SE 1.3
javac
java compiler
java
java interpreter
Example program

21. AL: java.net classes
Low-level networking classes (Sockets and Packets)
High-level URL networking classes
java.lang.Object
java.net.Socket
java.net.ServerSocket
java.net.DatagramSocket
java.net.MulticastSocket
java.net.DatagramPacket
java.net.URL
java.net.URLConnection
java.net.HttpURLConnection
java.net.URLencoder
java.net.InetAddress

22. AL: java.net.Socket Constructors Some methods Socket(InetAddress, int)
Socket(String, int)
Socket(InetAddress, int, InetAddress, int)
Some methods
getInputStream()
getOutputStream
getInetAddress()
getPort()
getLocalAddress()
getLocalPort()
get/set individual socket options

23. AL: java.net.ServerSocket
Constructors
Socket(int)
Socket(int, int) // backlog specified
Socket(int, int, InetAddress) // local address and backlog specified
Some methods
accept()
getInetAddress()
getLocalPort()

24. AL: Socket programming with TCP
Example client-server app:
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)
Input stream: sequence of bytes into process
Output stream: sequence of bytes out of process
outToServer
iinFromServer
inFromUser
client socket

25. AL: Java client/server socket interaction: TCP
Server (running on hostid)
Client
create socket,
port=x, for
incoming request:
welcomeSocket =
ServerSocket()
TCP
connection setup
close
connectionSocket
read reply from
clientSocket
create socket,
connect to hostid, port=x
clientSocket =
Socket()
wait for incoming
connection request
connectionSocket =
welcomeSocket.accept()
send request using
clientSocket
read request from
connectionSocket
write reply to

26. AL: 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());
Create
input stream
Create
client socket,
connect to server
Create
output stream
attached to socket

27. AL: Example: Java client (TCP), cont.
Create
input stream
attached to socket
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(); }
Send line
to server
Read line
from server

28. AL: 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()));
Create
welcoming socket
at port 6789
Wait, on welcoming
socket for contact
by client
Create input
stream, attached
to socket

29. AL: Example: Java server (TCP), cont
DataOutputStream outToClient =
new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence); }
Create output
stream, attached
to socket
Read in line
from socket
Write out line
to socket
End of while loop,
loop back and wait for
another client connection

30. AL: 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

31. AL: java.net.DatagramSocket
Constructors
DatagramSocket()
DatagramSocket(int) // bind to specific port
DatagramSocket(int, InetAddress) // specify local address
Some methods
getLocalAddress()
getLocalPort()
receive(DatagramPacket)
send(DatagramPacket)
get/set individual socket options

32. AL: java.net.DatagramPacket
Constructors
DatagramPacket(byte[], int) // receiving packets
DatagramPacket(byte[], int, InetAddress, int) // sending packets
Some methods
getAddress() // remote address
getPort() // remote port
getLength() // get packet length
getData() // return data received or to be sent
setAddress(InetAddress) // set remote address
setData(byte[]) // set packet data
setLength(int) // set packet length
setPort(int) // set remote port

33. AL: Client/server socket interaction: UDP
Server (running on hostid)
create socket,
clientSocket =
DatagramSocket()
Client
Create, address (hostid, port=x,
send datagram request
using clientSocket
create socket,
port=x, for
incoming request:
serverSocket =
DatagramSocket()
read request from
serverSocket
close
clientSocket
read reply from
clientSocket
write reply to
serverSocket
specifying client
host address,
port umber

34. AL: 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();
Create
input stream
Create
client socket
Translate
hostname to IP
address using DNS

35. AL: Example: Java client (UDP), cont.
Create datagram with data-to-send,
length, IP addr, port
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
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(); }
Send datagram
to server
Read datagram
from server

36. AL: Example: Java server (UDP)
import java.io.*;
import java.net.*;
class UDPServer {
public static void main(String args[]) throws Exception {
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
while(true)
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
Create
datagram socket
at port 9876
Create space for
received datagram
Receive
datagram

37. AL: Example: Java server (UDP), cont
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 addr
port #, of
sender
Create datagram
to send to client
Write out
datagram
to socket
End of while loop,
loop back and wait for
another datagram

38. AL: High-level Java networking classes
Socket/Packet
Low level building blocks
Must implement all application-level logic
Many protocols based on URLs and/or tunneled in http
Program at a higher-level to hide underlying protocol details
Do not re-implement http, URL parsing, mime handling for each application

39. AL: High-level client-side Java networking classes
java.net.URL
Represent a URL object
java.net.URLConnection
Represent a connection to a URL which can be read and written from
java.net.HttpURLConnection
Subclass of URLConnection for URLs

40. AL: High-level server-side Java networking classes
Servlets
Dynamically generate content
Implement common protocol header logic
Example http servlets
Cookies
Content-type
Content-length
Servlet classes
javax.servlet.Servlet
init()
service()
destroy()
javax.servlet.ServletRequest
javax.servlet.ServletResponse
javax.servlet.HttpServlet
javax.servlet.HttpServletRequest
javax.servlet.HttpServletResponse