So you want to build a chat app?
The most efficient way, both in terms of time and money, is to use an existing chat framework such as CometChat Pro. But, if you're dead set on building a chat application from scratch, you'll have a myriad of decisions to make. One of the most important decisions is how you're going to accomplish the core functionality of a chat app: sending messages between users.
More succinctly put, what instant messaging protocol will you rely on to facilitate real-time chat?
While many different communication protocols exist, in this article we are going to take a look at and compare two popular instant messaging protocols: XMPP vs. WebSocket. By the end, you'll have a better understanding of how these two protocols work, the roles they play in a chat app, and what each brings to the table.
A quick disclaimer: there is no obvious winner between the two chat protocols. Whether you end up using XMPP or WebSocket or even both (more on that later), the winner is the one which best suits your specific use cases and business requirements.
Keep reading to find your champion.
What Are XMPP and WebSocket?
It's hard to compare two things without first knowing what they are.
XMPP (short for Extensible Messaging and Presence Protocol) is an open standard communications protocol that allows for transmitting XML fragments between a server and client. A client, in this case, would be a browser or a mobile app. XMPP is one of the oldest and most widely supported instant messaging protocols. It has been in use for more than two decades.
The WebSocket protocol, on the other hand, is a modern chat messaging protocol. It provides a persistent channel that sends text and binary data in both directions. The data can even be sent simultaneously, if needed. These types of bidirectional channels are called full-duplex. While originally designed to facilitate the communication between a server and browser, WebSocket can be (and widely are) used in mobile apps.
Both XMPP and WebSocket are instant messaging protocols that can be used in chat apps to relay data back and forth. To get a better understanding of the differences between the two, let's take a look at the role they each play in a chat app.
What Role Does Each Protocol Play in a Chat App?
Have you heard of the OSI model? It's a conceptual framework that characterizes and describes the communication functions of a computing system. While the framework is nuanced, and both XMPP and WebSocket don't fit neatly into it, it's still helpful in understanding how each protocol interacts with the system as a whole.
There are 7 layers that make up the OSI model:
Each layer depends on the layers before it, building on top of the earlier layers to create the final model. If necessary, in the OSI model you can even stack multiple same-type layers on top of each other. For example, you can stack multiple transport layers on top of each other before adding on a session layer.
Why Does This Matter?
Well, both XMPP and WebSocket stack onto different layers in the OSI model. XMPP is an application layer protocol that defines the structure and syntax of XML fragments, called stanzas, which handle messaging, presence information, and contact lists. However, to send these stanzas, XMPP still relies on a transport protocol, such as a TCP/IP binding, HTTP/S, or a WebSocket connection.
Wait, what? XMPP can be stacked on top of WebSocket?
Yes, and this is where things get a little muddy...WebSocket is technically an application layer protocol just like XMPP. However, it doesn't conform to the OSI model. So, many people argue that it belongs on the transport or network layer. WebSocket requires a TCP/IP connection and acts as a thin transport layer on top of the TCP/IP connection. Unlike XMPP, it doesn't strictly define the structure of the data it transports and it doesn't, out-of-the-box, provide messaging capabilities, presence information, or contact list management. This is why, unless you plan on writing your own application layer messaging protocol, you have to stack a protocol like XMPP or WAMP on top of WebSocket to provide these chat functionalities.
Okay, to summarize: XMPP is concerned with providing a standard way to handle messaging, presence information and contact list management. It requires a transport layer protocol such as TCP, HTTP, or WebSocket to send this data back and forth. WebSocket, on the other hand, doesn't define the type of data you send and concerns itself with providing a bidirectional, persistent transport stream on top of a TCP connection. It must be paired with an additional protocol to provide full messaging functionality in the context of a chat app.
XMPP vs. WebSocket: Strengths & Weaknesses
Now that you have a better understanding of what role each protocol plays, let's compare XMPP and WebSocket in terms of the features you may be looking for in a chat protocol.
While security is somewhat of a moving target and nothing is ever 100% secure, it's an important consideration when deciding on a chat protocol.
XMPP provides security in the form of both identity and encryption. Clients are expected to authenticate (via their identity) both the host server and their messages. This cuts down on spoofing and spam. XMPP actually uses two types of encryption methods: SASL (Simple Authentication Security Layer) and TLS (Transport Layer Security).
SASL is used when the client and server attempt to first establish a connection. Once authorization takes place a connection is created and the data there-on-out is encrypted via TLS. Together these measures make XMPP quite secure. And if these built-in security features aren't enough, there are many XMPP plugins that extend the core functionality.
WebSocket is a newer, more modern protocol and, due to this, has fewer security standards. Out-of-the-box, WebSocket doesn't offer much in regards to security. Your only options are either WS or WSS—with WSS being the more secure of the two bindings as it transports over SSL or TLS. If you need more security than that (like authentication or authorization) you'll have to implement it yourself.
While WebSocket security is still evolving, the current clear winner in regards to security is XMPP.
Both XMPP and WebSocket are known for their extensibility. However, they are extensible in different ways.
Earlier we noted that each protocol works on a different layer of the OSI model. So, when talking about WebSocket's extensibility we are talking about extensibility on the transport layer. XMPP, on the other hand, deals with extensibility on the application layer.
WebSocket supports the implementation of more than 40 additional protocols on top of itself — XMPP, WAMP, and MQTT. You can also expand WebSocket functionality, such as providing data compression, via extensions.
Being on the application layer, XMPP extensibility looks a bit different. Most extensions developed for XMPP provide additional functionality to make XMPP suitable for specific applications such as file sharing, online games, and VoIP.
Given the nature of this difference, neither protocol strictly wins out against the other. When it comes to extensibility, what works better for you will largely depend on your chat app's requirements.
If you paid attention at the beginning of this article, you'll remember that the two protocols handle data types very differently. XMPP only allows you to send XML fragments while WebSocket allows you to send any binary or text data type (such as JSON).
Since you were definitely paying attention, you're probably thinking to yourself, "Unless I need XML, I should be using WebSocket."
Not so fast. XML is a text data type, and anything you want to send as JSON, you can easily send as XML. You can actually embed binary data in an XML fragment to bypass XMPP's limitations. However, keep in mind that XMPP isn't optimized to handle binary data and sending binary data is slower and requires additional parsing.
When it comes to data type handling, WebSocket is the clear winner. Being able to efficiently send binary data will cover almost all use cases including images, video and audio.
In a real-time chat app, the speed at which messages get delivered to the recipient is crucial.
Both XMPP and WebSocket are considered "real-time" protocols. However, their transmission speeds are actually different. Due to its decentralized nature, XMPP has to continuously authorize and authenticate the client and server—increasing bandwidth usage and slowing down connection speed. WebSocket is more centralized in nature due to its persistent connection between client and server. Not needing to reestablish the connection every time data gets sent gives WebSocket a large speed advantage.
The winner, when it comes to transmission performance, is WebSocket.
Pros and Cons of XMPP vs. WebSocket
Okay, now that we've learned the role each protocol plays and compared them through the lens of vital features, let's summarize:
Pros of XMPP and WebSocket Protocol
Cons of XMPP and WebSocket Protocol
As you can see from this list, choosing between WebSocket and XMPP isn't a matter of choosing which one's better. It's a matter of choosing which one's right for you. It largely depends on what you're looking for in an instant messaging protocol. There is no clear winner between the two protocols when comparing them at a high level.
Usage Examples of XMPP and WebSocket
XMPP and WebSocket are two of the most popular chat protocols on the internet. There are countless websites and apps that implement XMPP, WebSocket, or even both. If you're curious, here's a list:
Websites and apps that use XMPP:
WhatsApp uses their own proprietary variation of XMPP
Apple uses XMPP to deliver push notifications
Grindr, a geolocation-based dating application, uses XMPP for their chat functionality
Websites and apps that use WebSocket:
Trello, a collaborative task management app, uses WebSocket
Slack uses WebSocket on port 443
Discord, the popular gaming chat platform, also uses WebSocket
CometChat Pro too uses the WebSocket architecture for our Chat APIs and SDKs
What about apps that use both XMPP and WebSocket?
Well, Zoom is such an app. It uses XMPP for their chat functionality and WebSocket as a transport protocol.
Which Instant Messaging Protocol Should You Use?
Picking between XMPP and WebSocket for your chat app requires taking a hard look at your chat app's requirements.
If multiple types of data, especially binary data, need to be sent back and forth then WebSocket would be your preferred protocol.
If you need to open multiple connections per user, WebSocket is the one for you.
If you have major concerns about security, then XMPP is the protocol for you.
If you require built-in presence and messaging functionality, XMPP is your best choice.
If data transmission speed is a top priority, then WebSocket is the protocol you're looking for.
If you're looking for a vast ecosystem of plugins to extend functionality, XMPP is a great choice.
When deciding between the two, you shouldn't consider the issue to be XMPP vs. WebSocket. As you now know, you can use XMPP and WebSocket together. Leveraging WebSocket's persistent connection with XMPP's messaging and presence functionality might give you the security, flexibility, and speed required for your chat app.
If you're still on the fence about which protocol to choose, these resources can help you learn more:
About the author:
Cosette Cressler is a passionate content marketer specializing in SaaS, technology, careers, productivity, entrepreneurship and self-development. She helps grow businesses of all sizes by creating consistent, digestible content that captures attention and drives action.