MQTT vs AMQP for IoT Communications: Head to Head

With the exponential growth of the Internet of Things (IoT), managing communication between devices and systems is growing in importance. IoT communication is made possible by message queuing protocols such as MQTT and AMQP that facilitate the exchange of information in a structured and efficient manner.

Two popular protocols powering the IoT are the MQTT protocol (Message Queuing Telemetry Transport) and AMQP (Advanced Message Queuing Protocol). Let's explore each of these protocols in detail and explain their key differences and the factors to consider when choosing between the two.

Importance of Message Queuing Protocols

In IoT, devices ranging from simple sensors to complex machines need to communicate with each other and with central systems. These devices often operate in environments with constrained resources, such as low power or unreliable networks.

Message queuing protocols like MQTT, which is designed for such environments, enable these devices to communicate efficiently and reliably.

In distributed systems, components often need to exchange information while maintaining loose coupling. Protocols like AMQP, with its robust features and complex routing capabilities, provide a reliable means for this communication.

These protocols ensure that messages are delivered reliably, and the systems can scale and evolve independently.

What Is MQTT?

MQTT, short for Message Queuing Telemetry Transport, is a lightweight publish/subscribe messaging protocol. It was introduced by IBM in 1999.

Designed for constrained devices and low-bandwidth, high-latency, or unreliable networks, MQTT is perfect for machine-to-machine or IoT use cases where a small code footprint is required.

MQTT operates based on the publish/subscribe model. In this model, a producer, known as a publisher, creates messages, and a consumer, known as a subscriber, receives them.

The interaction between the publisher and subscriber is managed by a broker. The broker is responsible for distributing the messages from publishers to subscribers.

The simplicity of MQTT lies in its minimal protocol commands. It has only a handful of commands, making it easy to implement in various devices and systems.

Also, its quality-of-service levels allows for message delivery confirmation, ensuring that no message is lost in transmission. Let’s explore MQTT in more detail.

MQTT Transport and Framing

MQTT can use TCP, TLS, WebSocket, or QUIC as its transport layer, creating connections, establishing sessions, and transmitting messages reliably between clients and brokers.

MQTT frames consist of a 2-byte fixed header, a variable header, and a variable-length payload. The header contains information such as the packet type, quality of service level, remaining length, packet ID, and properties. The binary payload contains the actual message being transmitted.

MQTT defines 15 types of control packets based on the binary frames in the version 5.0 protocol specifications. Some of the common packets used to connect, publish and subscribe include CONNECT, CONACK, PUBLISH, PUBACK, and SUBSCRIBE.

MQTT QoS

MQTT supports three qualities of service for message delivery:

• QoS0 "At most once": Messages are delivered according to the best efforts of the operating environment; message loss can occur.
• QoS1 "At least once": Messages are assured to arrive, but duplicates can occur.
• QoS2 "Exactly once": Messages are assured to arrive exactly once.

MQTT Advantages and Disadvantages

Pros:

• Simplicity: The simplest publish-subscribe design, easier to set up, develop, and manage.
• Lightweight and Efficient: MQTT messages have only 2-type header overhead with low bandwidth usage making the protocol ideal for low-power, low-bandwidth devices.
• Scalability: Scale to tens of millions of MQTT connections, topics, and subscriptions.
• Reliable message delivery: Three Quality of Service levels to ensure reliable message delivery, even over unreliable networks.
• Low latency: Near real-time message delivery with one-digit millisecond latency due to the simple topic-based pub/sub model.
• Security: MQTT supports secure communications over TLS/SSL or QUIC and various authentication mechanisms using LDAP, JWT, PSK, and X.509 certificates.
• Compatibility and Integration: MQTT can be integrated with many programming languages, operating systems, and software platforms.

Cons:

• MQTT lacks store-and-forward queuing.

What is AMQP?

AMQP, Advanced Message Queuing Protocol, is a protocol that supports a wide range of messaging patterns and offers a robust set of features. It was created by J.P. Morgan Chase in 2003. It is designed for systems that require a high level of reliability and functionality.

Unlike MQTT, AMQP is a peer-to-peer protocol, meaning it supports direct communication between the producer and consumer.

AMQP uses a model where messages are sent to exchanges, which then route the messages to appropriate queues based on rules called bindings. The consumer then retrieves the message from the queue.

This model allows for complex routing and distribution strategies, making AMQP suitable for complex distributed systems.

The strength of AMQP lies in its extensive feature set. It supports a variety of message properties and delivery modes, including persistent messaging, which ensures the messages are not lost even if the broker restarts.

AMQP Exchange and Bindings

In AMQP, an exchange is like an email transfer agent that inspects email and decides on the basis of routing keys and tables. A routing key corresponds to an email with To:, Cc:, or Bcc: addresses, without server information (routing is internal within an AMQP server). A binding is like an entry in the email transfer agent’s routing table.

AMQP defines four types of exchanges:

1. Direct (point-to-point): Messages are routed directly to the queue bound to the exchange.
2. Fanout: Messages are routed to every queue bound to the exchange.
3. Topic (publish-subscribe): Messages are routed to queues based on the routing key and the binding pattern to the exchange.
4. Headers (publish-subscribe): Messages are routed to queues based on pattern matching of message headers.

AMQP Transport and Framing

AMQP is a binary protocol built on TCP/IP, where a reliable, persistent, stream-oriented connection is established between a client and a broker. Multiple channels can be opened on a single socket connection, allowing multiple streams of data to be transferred simultaneously.

AMQP frames in version 1.0 consist of an 8-byte fixed header, an optional extended header, and a variable-length binary payload. The fixed header contains information about the frame type, channel number, and size of the payload.

The payload contains the actual message being transmitted, along with any associated metadata.

AMQP Advantages and Disadvantages

Pros:

• Store-and-forward queuing: AMQP supports store-and-forward queuing at the expense of some efficiency and additional complexity (compared to MQTT).
• Flexible message routing: AMQP provides flexible message routing, including point-to-point, publish-subscribe, and fan-out.
• Security: AMQP supports security measures such as TLS and SASL for encryption and authentication.
• Ecosystem: AMQP has a large and mature ecosystem of open-source server implementations and client libraries for various programming languages.

Cons:

• Complex: AMQP introduces many concepts in its model and can be complex and challenging to understand, set up, and manage.
• Heavyweight: AMQP introduces multiplexing in its transport layer with “channels.” Each AMQP frame has a header overhead of 8 bytes.
• Backward compatibility: The biggest problem of AMQP is that versions 0.9.1 and 1.0 are completely different, leading to more complexity in this solution space.
• Scalability and performance: AMQP may have limited scalability and low performance in some use cases. This is due to its architecture, which imposes greater complexity and overhead compared to lightweight protocols like MQTT.

MQTT vs AMQP: Head-to-Head

The following table summarizes our comparison between AMQP and MQTT.

Factors to Consider when Choosing

When faced with a decision between MQTT vs AMQP, there are several factors to consider.

Evaluation Based on Use Case Requirements

The choice between MQTT and AMQP largely depends on the use case requirements. If you are dealing with constrained devices or unreliable networks, MQTT with its lightweight nature might be the better option. If your use case requires complex routing and high reliability, then AMQP would be more suitable.

Evaluation Based on System Architecture

The system architecture also plays a role in the decision. MQTT's simplicity makes it a good choice for systems with a clear and simple communication model. AMQP, with its flexibility and robust feature set, is better suited for complex systems with diverse communication needs.

Evaluation Based on Network Conditions

Network conditions are another critical factor. MQTT performs well in low-bandwidth, high-latency, or unreliable networks. AMQP, on the other hand, requires a reliable network connection due to its higher overhead.

Evaluation Based on Required Quality of Service

MQTT provides three levels of quality of service, allowing for flexibility in message delivery guarantees. AMQP, with its persistent messaging, ensures high reliability in message delivery.

Making Your Decision

Both MQTT and AMQP have their strengths and are suited for different scenarios. Understanding their key differences and evaluating your requirements against these differences will help you make an informed decision when choosing. Remember, the right choice depends on your specific needs and constraints.