High Performance Browser Networking

Chapter 3. Building Blocks of UDP

User Datagram Protocol, or UDP, was added to the core network protocol suite in August of 1980 by Jon Postel, well after the original introduction of TCP/IP, but right at the time when the TCP and IP specifications were being split to become two separate RFCs. This timing is important because, as we will see, the primary feature and appeal of UDP is not in what it introduces, but rather in all the features it chooses to omit. UDP is colloquially referred to as a null protocol, and RFC 768, which describes its operation, could indeed fit on a napkin.

Datagram

A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination nodes without reliance on earlier exchanges between the nodes and the transporting network.

The words datagram and packet are often used interchangeably, but there are some nuances. While the term “packet” applies to any formatted block of data, the term “datagram” is often reserved for packets delivered via an unreliable service—​no delivery guarantees, no failure notifications. Because of this, you will frequently find the more descriptive term “Unreliable” substituted for the official term “User” in the UDP acronym, to form “Unreliable Datagram Protocol.” That is also why UDP packets are generally, and more correctly, referred to as datagrams.

Perhaps the most well-known use of UDP, and one that every browser and Internet application depends on, is the Domain ...