The table below contains a quick summary of the IoT protocols:

Protocol CoAP XMPP RESTful HTTP MQTT AMQP
Transport UDP TCP TCP TCP TCP
Messaging Request/Response Publish/Subscribe Request/Response Request/Response Publish/Subscribe Request/Response Topic based Publish/Subscribe
2G, 3G, 4G Suitability (1000s nodes) Excellent Excellent Excellent Excellent Excellent
LLN Suitability (1000s nodes) Excellent Fair Fair Fair Excellent
Compute Resources 10Ks RAM/Flash 10Ks RAM/Flash 10Ks RAM/Flash 10Ks RAM/Flash 10Ks RAM/Flash
Success Stories Utility Field Area Networks Remote management of consumer white goods Smart Energy Profile 2 (premise energy management, home services) Extending enterprise messaging into IoT applications Extending enterprise messaging into IoT applications
designed for resource-constrained devices and low bandwidth, high latency networks interoperability
reliable queuing, flexible routing, transactions, and security

Source: Beyond MQTT: A Cisco View on IoT Protocols, Paul Duffy, April 30 2013