TCP is a connection-based protocol that provides reliable data transfer between computers. It is based on a four-layer model and provides ordered, error-free transmission of data through features like flow control and congestion control. Java's java.net package supports system-independent network communication. URLs identify Internet resources and have a standardized syntax consisting of parts like the protocol, host, port, and file name. Sockets represent endpoints for two-way communication between programs over a network, while server sockets listen for and accept client connections on a specific port. UDP is a lightweight alternative to TCP that is faster but unreliable and unordered.

1. Networking

2. TCP
connection-based protocol that provides a
reliable flow of data between two computers.
TCP is based on a four-layered model.
HTTP, FTP – High level protocol
TCP, UDP – Open, maintain connection
IP – Transmits packet from one IP add to
another
IP – Physical equipment such as twisted
pair cables

3. Data transfer
Ordered data transfer
Retransmission of lost packets
Error-free data transfer
Flow control
Congestion control

4. Java provides the java.net package to perform
system-independent network communication

5. Networking basics
A computer generally has a single physical
connection available for the network.

6. Port
The physical connection is numbered within a range of 0 to
65535, called Ports.
Ranges from 0 to 1023 are reserved for HTTP, FTP …
Data transmitted is accompanied with the destination
address and the port number.

7. URL
Uniform Resource Locator
a reference or an address to a resource on
Internet.
Two parts:

8. URL
Resource name contains:
Host name
File name
Port number

9. What different?
http://vn.yahoo.com:80/index.html
http://vn.yahoo.com/index.html
http://vn.yahoo.com/

10. URL
Constructors:
URL(String url)
URL(String protocol, String host, String file)
URL(String protocol, String host, int port,
String file)
URL(URL baseURL, String relativeURL)

11. Methods of URL
public String getHost()
public String getFile()
public String getPath()
public final InputStream openStream()

12. Methods of InetAddress
public String getHostAddress()
public String getHostName()
public static InetAddress getLocalHost()
public static InetAddress getByName(String host)

13. URLConnection
Abstract class represents the communication link
between an application and a URL.
Used to read from and to write to the resource
referenced by the URL.

14. URLConnection
Cannot instantiate a URLConnection obj directly.
Create URLConnection obj by method
openConnection() of URL class
. openConnection()
. getInputStream()
. getOutStream()

15. Socket
one end-point of a two-way communication link
between two programs running on the network

16. Socket
Socket(String host, int port)
UnknowHostException
OIException

17. Socket
Retrieve the InputStream from the socket
Retrieve the OutputStream from the socket
Read from the InputStream
Write the OutputStream

18. ServerSocket
represents the server side.
If the ServerSocket successful in binding to a
port, I can then wait and listen for client request
public ServerSocket(int port) throws IOException

19. ServerSocket
Steps:
. Initiate ServerSocket obj
. accept()
. OutputStream
. InputStream

20. UDP – User Datagram Protocol
sent message, referred to as datagrams, to other
host

21. UDP – User Datagram Protocol
Unreliable
Not ordered
Lightweight
No congestion control

22. UDP
Time-sensitive applications often use UDP
VoIp
Online games

23. DatagramPacket
create a datagram packet.
Constructors:
DatagramPacket(byte[], int)
DatagramPacket(byte[], int, InetAddress, int)
buf, length, address, port

24. DatagramSocket
represents a socket for sending and receiving
datagram packets.
Constructors:
DatagramSocket(int)
DatagramSocket(port, InetAddress)

25. Methods of DatagramSocket
public void send(DatagramPacket p)
public void receive(DatagramPacket p)

26. Methods of DatagramPackets
public InetAddress getAddress()
public int getPort()
public byte[] getData()
public void setData(byte[] data)
public void setPort(int port)