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I have a doubt about the IoT Protocol Stack . Searching between papers on google scholar or IEEE about IoT , i find the actual "IoT Protocol Stack" : IoT Stack I think it is uncorrect . The doubt is about the transport layer and application layer.

1) why there is only CoAP on the application layer if there are many others Application Layer Protocol for the IoT , such as : MQTT, XMPP ,AMQP , WebSockets and so on?

2) Why they provide only UDP at the Transport layer if in the upper layer ( Application) there are some important protocol in the environment of the IoT , for example MQTT, that run over TCP ?

Salsa94
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    Questions here need to be clear, singular, and specific. You appear to be trying to do a survey of options but are mixing up too many distinct things (some of which are purely matters of opinion or preference) at once to have an answerable question. – Chris Stratton Mar 08 '19 at 04:11

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The term "IoT" is used with various meanings by different interest groups; so is therefore the term "IoT stack".

What the linked image depicts is the IETF IoT Stack, which is the IETF's idea of what IoT devices should use to deserve that name. CoAP is the application protocol specified by IETF (and used by various others like OMA LwM2M, OCF or Thread), and is in my experience the best suited protocol as it allows full operation on tiny devices (technically: Class 0 according to RFC 7228 – good luck implementing XMPP, WebSockets or similar on those) while still being powerful enough to express all the concepts from the HTTP web.

The image depicting only UDP is probably due to the focus on IoT devices: While CoAP can be transmitted over several transport layers (including TCP and WebSockets, but also SMS in a draft version), those transports are rather used indirectly (eg. by a browser application that uses a gateway to talk to UDP connected devices), the expected scenario for the devices themselves is using CoAP over UDP on a 6LoWPAN network. That doesn't rule out other deployment scenarios (eg. LwM2M uses CoAP over cellular networks a lot, in UDP and TCP transports), but is better seen as typical example for the smallest of devices.

Community
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chrysn
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