Formats of communication agreed-upon and used by hardware and software systems to exchange messages and transmit information: rules of semantics, syntax, synchronizing, and error recovery.

AMQP 0-9-1

Message queueing protocol used by Ably and RabbitMQ, entirely different from AMQP 1.0 (used by Azure Service Bus).

AMQP 1.0

Message queueing protocol used by Azure Service Bus, entirely different from AMQP 0-9-1 (used by Ably and RabbitMQ).


Communications protocol complementary to HTTP, allowing bidirectional message streaming over a single TCP connection.

Long polling

Variant of the polling technique used to emulate a push mechanism where pushes are not possible or disallowed.


The second major version of the Hypertext Transport Protocol.


HTTP/3 is the latest iteration of the original HTTP protocol, which powers the World Wide Web (WWW).


Open, event-driven push transport protocol for distributed pub/sub communications using webhooks.

Server-Sent Events

Server-push technology used for servers to automatically update clients subscribed to event-streams.


Event-driven JavaScript library used for bi-directional communication, using WebSockets (with polling as fallback).


Lightweight, low-bandwidth pub/sub network protocol used for ordered, lossless, bi-directional connections.