Messaging

A crucial aspect of communication. Most protocols are proprietary. Open standards exist for interoperability.

Types

• Real-time messaging
  Messages delivered immediately. Both parties must be online simultaneously. Examples: XMPP, Matrix.
• Store-and-forward
  Messages stored at intermediate servers and delivered when the recipient is available. Examples: email (SMTP), MQTT with persistent sessions.

XMPP

Aka. eXtensible Messaging and Presence Protocol. Open standard for messaging. Anyone can run a server; servers can interconnect. Messages are XML-based. Supports presence, attachments, and group chats.

Versions of XMPP are used in WhatsApp and Google. Also used for IoT messaging.

MQTT

Aka. Message Queuing Telemetry Transport. Lightweight publish-subscribe protocol. Designed for constrained devices on low-bandwidth, high-latency networks.

Key concepts:

• Broker
  Central server that receives all messages and routes them to subscribers.
• Topics
  Hierarchical string identifiers used to route messages (e.g. home/sensor/temperature).
• QoS levels
  0 = at most once, 1 = at least once, 2 = exactly once.

Standard for sensor-to-cloud communication in IoT.

AMQP

Aka. Advanced Message Queuing Protocol. Open standard for message-oriented middleware. Supports queuing, routing (point-to-point and publish-subscribe), reliability, and security.

Used in enterprise messaging systems. RabbitMQ is a popular AMQP broker.

Matrix

Open standard for decentralized, real-time communication. Servers federate: users on different homeservers can communicate. Supports end-to-end encryption, rooms, and bridging to other protocols.

Used by Element. Designed as an open alternative to proprietary chat platforms.

Protocol Comparison