What is the UDP protocol?

The UDP protocol is a connectionless protocol that is well suited for real-time, high-bandwidth applications such as online gaming. This is because it has low latency and is able to handle high throughput. Just so we are on the same page, in the world of network terms, latency refers to the time between the transmission and receiving of data through the network.

For instance, it’s very common to talk about lag in online multiplayer games: the time between the player performing an action and the game reacting to it. The next figure illustrates how latency works and is calculated:

Figure 1.2 – Visual demonstration of latency

It’s basically how much time it takes for data to cross the network, be properly handled by the server, and to provide a response to the client.

Throughput refers to how much data we can send through a given network route within a time period before it gets overwhelmed. For instance, this is a fundamental concept when we talk about DDoS attacks, where hackers overwhelm the server with an immense number of unsolved requests, preventing other clients from accessing the service. In the following figure, you can see a visual representation of the throughput concept:

Figure 1.3 – Visual demonstration of throughput

The bandwidth is how big the available channel of communication in the network is. You can think of it as a pipe that streams data. A bigger pipe allows a lot of data, and big data, to be transmitted at any given time, while a small pipe may not even allow any data, of any size, to be transmitted. You can see this concept illustrated in the following figure:

Figure 1.4 – Visual demonstration of bandwidth

Unlike the more commonly used Transmission Control Protocol (TCP), User Datagram Protocol (UDP) does not establish a dedicated connection between two devices before transmitting data. Instead, it simply sends packets of data to a specified destination address without ensuring that the packets have been received or acknowledged.

Sounds… bad, right? But it’s quite the opposite.

This lack of reliability is often seen as a drawback of UDP, but in the context of online multiplayer games, it can actually be an advantage. In games, where responsiveness and low latency are critical, the overhead of establishing and maintaining a connection can be a significant bottleneck.

By not requiring a dedicated connection, UDP allows for faster and more efficient transmission of data. Additionally, since UDP does not require the receiver to acknowledge receipt of packets, it is less affected by network congestion or delays, which can be critical for maintaining a stable and responsive connection in a high-bandwidth, high-latency environment such as online gaming.

Furthermore, the lack of reliability of UDP can actually be beneficial in the context of online multiplayer games. In games, where a small amount of packet loss or delay can have a large impact on the players’ experience, it’s important that the game can adapt to these types of network conditions. By not providing guarantees on packet delivery, UDP allows the game to handle packet loss and delay in a way that is most appropriate for the specific game and its mechanics.

Think about the following situation.

We establish a connection. In this connection, we update all players in the network about all other player avatars’ positions in the world. This way, everyone shares the same world state.

If we use a TCP protocol, everyone will have to wait for every other player to send their position and confirm that they have received every change in every other player’s position, while also trying to maintain the correct chronological order in which the positions have changed.

So, in this example, if a player moves five units to the left and sends 15 packets with all the movement data, including being idle, all other players must confirm that they have received all those 15 packets.

Using UDP, players can ignore every update but the latest one, which is the only relevant piece of information in real-time experience: what is the game-world state now? It doesn’t matter how it gets to this point; it only matters that it is there at this very moment.

We are going to see that this causes some trouble as well. But we can create methods and understand techniques to mitigate those issues. We are going to talk about that in further chapters.