QoS Strategies for Wireless Multimedia Sensor Networks in the Context of IoT at the MAC Layer, Application Layer, and Cross-Layer Algorithms

Table 3

Differences and problems with application layer protocols.

Protocol	Architecture	Transport	QoS options	Security	Weaknesses
CoAP	Request/response	UDP		DTLS	No in-built security features. DTLS does not support multicast
MQTT	Publish/subscribe	TCP		TLS/SSL	Insufficient security at the protocol level since payload values are not encrypted
SMQTT	Publish/subscribe	TCP		CP/KP-ABE	Key revocation and group pub/sub for distributed SMQTT are still a challenge
MQTT-SN	Publish/subscribe	UDP		TLS/SSL	SSL/TLS suffers from attacks like BEAST, CRIME, RC4, and Heartbleed
XMPP	Request/response; Publish/subscribe	TCP	X	TLS/SSL	Susceptible to spamming attacks and lacks worldwide support
AMQP	Publish/subscribe	TCP		TLS/SSL	Inappropriate for real-time applications
DDS	Publish/subscribe	TCP/UDP		TLS/SSL	Memory intensive and no open-source libraries for constrained devices
REST	Request/response	HTTP	X	HTTPS	Hard to implement. Uses HTTP, so incompatible with constrained apps
WebSockets	Publish/subscribe; Client/server	TCP	X	TLS/SSL	Bad user experience for IoT apps since it runs the client/server architecture
STOMP	Client/server	TCP		HTTP	The broker can act as a bottleneck