Chapter 14 User Datagram Protocol (UDP) Notes Textbook

Chapter 14 User Datagram Protocol (UDP) Notes

Objectives

• Introduce UDP and its relation to TCP/IP protocols.
• Explain UDP packet format and header field uses.
• Discuss UDP services (process-to-process delivery, multiplexing, demultiplexing, and queuing).
• Calculate the optional checksum, including pseudoheader usage.
• Explain the benefits of UDP for certain applications.
• Overview of UDP package structure.

Chapter Outline

• 14.1 Introduction
• 14.2 User Datagram
• 14.3 UDP Services
• 14.4 UDP Application
• 14.5 UDP Package

14-1 Introduction

• Position of UDP: UDP operates between the application layer and the IP layer, facilitating communication between application programs and network operations.

14-2 User Datagram

• Packet Structure: Each UDP packet has a fixed-size header of 8 bytes, which includes:
  • Source port number (16 bits)
  • Destination port number (16 bits)
  • Total length (16 bits)
  • Checksum (16 bits)
• Data Length: The data size can range from 0 to 65,507 bytes, as the total UDP packet size can be up to 65,535 bytes once the header is included.

Example 14.1 - UDP Header Analysis

• Header Breakdown from Hexadecimal Dump:
  • Source port number: CB84 (hex) = 52100 (dec)
  • Destination port number: 000D (hex) = 13 (dec)
  • Total length: 001C (hex) = 28 bytes
  • Data length: 28 - 8 = 20 bytes
• Direction of Packet: Since the destination port is a well-known port (13), it indicates a client-to-server direction.

14-3 UDP Services

• Services Provided by UDP:
  • Process-to-process communication
  • Connectionless service (no establishment of connection before data transfer)
  • Flow control, error control, and congestion control are minimal.
  • Queuing and multiplexing/demultiplexing capabilities.
  • Comparison with generic simple protocols.

Well-Known UDP Ports (Table 14.1)

• Port 7: Echo
• Port 9: Discard
• Port 13: Daytime
• Port 53: DNS
• Port 69: TFTP
• Port 123: NTP, etc.

Checksum Calculation

• Importance of Checksum: Optional for error detection but involves calculating using a pseudoheader including:
  • 32-bit source address
  • 32-bit destination address
  • Protocol number (8-bit)
  • Total UDP length (16-bit)
• Padding: May be needed for odd-length data during checksum calculation.

14-4 UDP Applications

• Typical Applications of UDP:
  • Ideal for applications needing fast, efficient transfer where delays are detrimental.
  • DNS requests are short and fit within a single user datagram, making UDP suitable.
  • Applications like SMTP, requiring large messages, face issues with UDP's unordered delivery.
  • Real-time applications (e.g., video streaming) prefer UDP, as missing frames can be ignored without major impacts.

14-5 UDP Package Structure

• Components of the UDP package:
  • Control-Block Table: Keeps track of active connections.
  • Input Queues: Handle incoming user datagrams.
  • Input Module: Manages incoming data processing.
  • Output Module: Handles data transmission.

Control Block Module (Table 14.2)

• Manages process IDs and port numbers, ensuring all entries are utilized efficiently.

Input Module (Table 14.3)

• Manages incoming data, allocating queues as necessary for processing.

Output Module (Table 14.4)

• Responsible for creating and sending user datagrams.

Example Scenarios in the Control-Block Table (Table 14.6-14.7)

• Illustrate the process flow with arrival and processing of user datagrams, showing state changes in the control-block table.

Summary of UDP

• Connectionless Protocol: Optimized for performance over reliability in specific use cases, making it an important part of the TCP/IP protocol suite while also highlighting where it may fall short against more reliable protocols like TCP.