MSDN Documentation

User Datagram Protocol (UDP)

The User Datagram Protocol (UDP) is a transport layer protocol that provides a simple, connectionless communication service. Unlike TCP, UDP does not guarantee delivery, order, or duplicate protection of datagrams. It is often used for applications where speed is more critical than reliability, or where the application layer handles reliability mechanisms.

Key Characteristics of UDP:

• Connectionless: No handshake is required before sending data.
• Unreliable: Datagrams may be lost, duplicated, or arrive out of order.
• Datagram-oriented: Data is sent in discrete packets called datagrams.
• Low Overhead: Minimal header information leads to faster transmission.
• Suitable for: Real-time applications like streaming media, online gaming, DNS, and VoIP.

UDP Header Format:

The UDP header is very small, consisting of only four fields, each 16 bits (2 bytes) in length:

• Source Port (16 bits): Identifies the port number of the sending application.
• Destination Port (16 bits): Identifies the port number of the receiving application.
• Length (16 bits): The length of the UDP header plus the length of the UDP data. The minimum length is 8 bytes (header only).
• Checksum (16 bits): An optional checksum for error detection. If not used, the field is set to zero.

The UDP header is 8 bytes long.

When to Use UDP:

UDP is an excellent choice when:

• Low latency is critical: For applications like live video streaming or online gaming, a small delay is preferable to waiting for retransmissions.
• Data loss is acceptable or handled by the application: If a lost packet is not catastrophic, or if the application can detect and recover from it, UDP is efficient.
• Broadcasting or Multicasting is needed: UDP supports sending data to multiple recipients simultaneously.
• Network conditions are reliable: In some controlled network environments, packet loss might be minimal.

Comparison with TCP:

Example UDP Packet Transmission (Conceptual):

// Client sends a UDP packet to a server
// Socket created for UDP communication
Socket udpSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

// Server's IP address and port
IPEndPoint serverEndPoint = new IPEndPoint(IPAddress.Parse("192.168.1.100"), 12345);

// Data to send
byte[] sendData = Encoding.ASCII.GetBytes("Hello, UDP Server!");

// Send the data
int bytesSent = udpSocket.SendTo(sendData, serverEndPoint);

// Client might wait for a response (or not, depending on application logic)
byte[] receiveData = new byte[1024];
EndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
int bytesReceived = udpSocket.ReceiveFrom(receiveData, ref remoteEndPoint);

string response = Encoding.ASCII.GetString(receiveData, 0, bytesReceived);
Console.WriteLine($"Received from server: {response}");

udpSocket.Close();

// Server receives a UDP packet
// Socket created for UDP communication
Socket udpServerSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, 12345);
udpServerSocket.Bind(localEndPoint);

byte[] receiveBuffer = new byte[1024];
EndPoint clientEndPoint = new IPEndPoint(IPAddress.Any, 0);

int bytesRead = udpServerSocket.ReceiveFrom(receiveBuffer, ref clientEndPoint);
string receivedMessage = Encoding.ASCII.GetString(receiveBuffer, 0, bytesRead);
Console.WriteLine($"Received from client ({clientEndPoint}): {receivedMessage}");

// Server sends a response
byte[] responseData = Encoding.ASCII.GetBytes("UDP Server acknowledges!");
udpServerSocket.SendTo(responseData, clientEndPoint);

udpServerSocket.Close();
            

Related Topics:

• Transmission Control Protocol (TCP)
• Sockets Programming
• Internet Protocol (IP)