User Datagram Protocol (UDP)

User Datagram Protocol (UDP)
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Overview

Specification:
- RFC 768
Purpose:
- Provide a mechanism for applications to send and receive messages
Assumptions:
- IP is used as the underlying network/internetwork layer protocol
- Applications are associated with ports

Properties

Not Connection/Session-Oriented:
- No handshaking
- No state information
Unreliable:
- Delivery is not guaranteed
- Order is not guaranteed
- Duplication protection is not provided
Message-Oriented:
- Transmission of complete messages
Not Controlled:
- No flow control
- No congestion control

The Demultiplexing Process

Recall:
- UDP needs to know what process/application to deliver datagrams to
The Socket:
- The process/application can be characterized by a two-tuple (called a socket) consisting of the destination IP address (which is in the IP frame) and port (which is in the UDP frame)

Moving through the Stack/Layers

Moving Down:
- The UDP segment becomes the payload of the IP datagram
Moving Up:
- The payload of the UDP datagram is handed off to the process bound to the destination port

Required Functionality of "Receivers"

Required Functionality of "Senders"

Header Format

Common Application-Layer Protocol Styles Using UDP

Sender and Receiver:
- One participant sends (periodic) messages
- One participant receives (periodic) messages
Requestor and Responder:
- One participant sends (periodic) requests
- One participant responds to (periodic) requests
Registrant and Responder:
- One participant registers and later unregisters
- One participant maintains a list of registered participants and sends to them
Registrant and Responder with Heartbeat/Confirmation:
- One participant registers and later unregisters
- One participant maintains a list of registered participants and sends to them
- Either the registrant periodically sends a heartbeat or the registrar periodically requests confirmation