The document outlines the use of DatagramSockets in Java for network communication via UDP, highlighting its advantages in applications like live TV coverage and online gaming where speed is prioritized over reliability. It details the steps for creating DatagramSockets and DatagramPackets, and provides sample server and client code implementations for both unicast and multicast communication. Additionally, it includes references for further learning through YouTube and GitHub.

1. Distributed Systems
Lecture -2-
Created by :
Eng. Ghadeer Al Hasan
UDP

2. Intro 1
- DatagramSockets are Java’s mechanismfor network communication via UDP insteadof
TCP.
- Java provides DatagramSocket to communicate over UDP insteadof TCP.
- DatagramSockets can be usedto both send and receive packets over the Internet.

3. Intro… 2
- It is preferredover TCP is the live coverage of TV channels.
- In this aspect, we want to transmit as many frames to live audience as possible not worrying about
the loss of one or two frames.(TCP being a reliable protocol add its own overhead while transmission)
- Another example where UDP is preferred is online multiplayer gaming.
- In games likecounter-strike or call of duty, it is not necessaryto relayall the information but the
mostimportant ones.
- It should also be noted that most of the applications in real life uses careful blendof both UDP and
TCP; transmitting the critical data over TCP and rest of the data via UDP.

4. Java Datagram programming model Steps

5. 1st Step 4
1- Creation of DatagramSocket: - First, a datagramSocket object is createdto carry the
packet to the destination and to receive it whenever the server sends any data.
To createa datagramSocket followingconstructors can be used:
protected DatagramSocket DatagramSocket()
protected DatagramSocket DatagramSocket(int port)
protected DatagramSocket DatagramSocket(int port, InetAddress inetaddress)
What is
port?

6. 2nd Step 5
2 - Creation of DatagramPacket: In this step, the packet for sending/receiving data via a
datagramSocket is created.
Constructor to senddata:
DatagramPacket(byte buf[], int length, InetAddress inetaddress, int port)
Parameters:
buf - the packet data.
offset - the packet data offset.
length - the packet data length.
address - the destination socket address.
Constructs a DatagramPacket for sending data at specifiedaddress and specifiedport.

7. 2nd Step… 6
Constructor to receive the data:
DatagramPacket(byte buf[], int length)
Parameters:
buf - thepacket data.
length- the packet data length.
Constructs a DatagramPacket for receiving the data of lengthlengthin the byte array buf.

8. 3rd Step 7
Invoke a send() or receive() call on socket object
void send(DatagramPacket packet)
void receive(DatagramPacket packet)

9. Server side Implementation

10. 9DatagramSocket socket = null;
byte[] receiverBuffer = null;
DatagramPacket receivePacket = null;
private void initializeVarible(){
try {
socket = new DatagramSocket(Constants.PORT);
receiverBuffer = new byte[Constants.BUFFER_SIZE];
} catch (SocketException ex) {
log("initializeVarible : " + ex.getMessage());
}
}
private String receiveData(){
String line = "";
try {
receivePacket = new
DatagramPacket(receiverBuffer,receiverBuffer.length);
socket.receive(receivePacket);
line = new
String(receivePacket.getData(),0,receivePacket.getLength());
} catch (IOException ex) {
log("receiveData : " + ex.getMessage());
}
return line;
}

11. 10
public static void main(String[] args){
Server server = new Server();
server.initializeVarible();
server.connecting();
}
private void connecting(){
while(true){
String data = receiveData();
log("Client : " + data);
if(data.equals(Constants.STOP)){
log("Client say bye...Exiting");
break;
}
receiverBuffer = new byte[Constants.BUFFER_SIZE];
}
}

12. Client side Implementation

13. 12Scanner scan = null;
DatagramSocket socket = null;
byte[] buffer = null;
private void initializeVarible(){
try {
scan = new Scanner(System.in);
socket = new DatagramSocket();
} catch (SocketException ex) {
log("initializeVarible : " + ex.getMessage());
}
}
private void send(String message){
try {
InetAddress ip = InetAddress.getLocalHost();
buffer = message.getBytes();
DatagramPacket packetSend = new
DatagramPacket(buffer,buffer.length,ip,Constants.PORT);
socket.send(packetSend);
} catch (IOException ex) {
log("send : " + ex.getMessage());
}
}

14. 13
private void connecting(){
while(true){
String line = readFromKeyboard();
send(line);
if(line.equals(Constants.STOP)){
break;
}
}
}
private String readFromKeyboard(){
String line = scan.nextLine();
return line;
}
public static void main(String[] args){
Client client = new Client();
client.initializeVarible();
client.connecting();
}

15. Run 14

16. Multicast Example

17. Server Side 16
MulticastSocket socket = null;
byte[] buffer = null;
DatagramPacket receivePacket = null;
Scanner scan = null;
private void initializeVarible() {
try {
socket = new MulticastSocket();
buffer = new byte[Constants.BUFFER_SIZE];
scan = new Scanner(System.in);
log("Server Running...");
} catch (SocketException ex) {
log("initializeVarible : " + ex.getMessage());
} catch (IOException ex) {
log("initializeVarible : " + ex.getMessage());
}
}

18. Server Side… 17
private String readFromKeyboard(){
String line = scan.nextLine();
return line;
}
private void send(String message) {
try {
InetAddress ip = InetAddress.getByName(Constants.IP);
buffer = message.getBytes();
DatagramPacket packetSend = new DatagramPacket(buffer, buffer.length,
ip, Constants.PORT);
socket.send(packetSend);
log("Message Sent");
} catch (IOException ex) {
log("send : " + ex.getMessage());
}
}

19. Server Side… 18
private void connecting() {
while (true) {
String data = readFromKeyboard();
send(data);
buffer = new byte[Constants.BUFFER_SIZE];
}
}
public static void main(String[] args) {
Server server = new Server();
server.initializeVarible();
server.connecting();
}

20. Client Side 19
MulticastSocket socket = null;
byte[] buffer = null;
DatagramPacket packet = null;
InetAddress ip = null;
private void initializeVarible() {
try {
socket = new MulticastSocket(Constants.PORT);
ip = InetAddress.getByName(Constants.IP);
buffer = new byte[Constants.BUFFER_SIZE];
} catch (SocketException ex) {
log("initializeVarible : " + ex.getMessage());
} catch (IOException ex) {
log("initializeVarible : " + ex.getMessage());
}
}

21. Client Side… 20
private String receiveData() {
String line = "";
try {
packet = new DatagramPacket(buffer, buffer.length);
socket.receive(packet);
line = new String(packet.getData(), 0, packet.getLength());
} catch (IOException ex) {
log("receiveData : " + ex.getMessage());
}
return line;
}
private void joinGroup(){
try {
socket.joinGroup(ip);
log("Client Running...");
} catch (IOException ex) {
log("joinGroup : " + ex.getMessage());
}
}

22. Client Side… 21
private void connecting(){
joinGroup();
while(true){
String line = receiveData();
log("Client Received : " + line);
}
}
public static void main(String[] args){
Client client = new Client();
client.initializeVarible();
client.connecting();
}

23. Run 22

24. References 24
- YouTube link
https://www.youtube.com/playlist?list=PLtDIUAtyP4lhV7CsYfLuIx26UeG4J-ujZ
- GitHub
https://github.com/Ghadeerof

25. End Lecture