Connectivity Framework Annex E : Assessment Template : CoAP
E . 6.4 Functional Viewpoint E . 6.4.2 Core Transport Layer Functions
Messaging Protocol ( Section 5.1.1 )
Communication Modes ( Section 5.1.2 )
Endpoint Addressing ( Section 5.1.3 )
Connectedness ( Section 5.1.4 )
Prioritization ( Section 5.1.5 )
Timing & Synchronization ( Section 5.1.6 )
Message Security ( Section 5.1.7 )
Does it require UDP or TCP ? What are the salient aspects of the messaging protocol ? What are the message size limitations ? What are the usage assumptions ? Is it optimized for certain message requirements ?
The CoAP messaging protocol is a IP based protocol . It supports multiple bindings that are based on IP ( i . e ., UDP , TCP , SMS , Web Sockets ). By default , it works over UDP . CoAP messages size is based on a 32-bit integer but CoAP messages work best without fragmentation , as such implementations tend to keep message sizes less than the underlying network transport layer payload sizes . A CoAP message , appropriately encapsulated , should fit within a single IP packet to packet to avoid IP fragmentation . When necessary CoAP does provide a mechanism to fragment and reassemble larger messages sizes . Which communication modes does it support ?
CoAP supports both unicast ( default ) and multicast ( when available by the underlying transport ).
Describe the transport endpoints . How are the endpoints addressed ? What are the limitations , if any , on the number of endpoints ?
A transport endpoint is a server IP address and a port number . There is no inherent limitation on the number of endpoints . Does it require a connected circuit between the endpoints ? Summarize the salient aspects . CoAP does not require a connected circuit between a client and server . Does it provide a means to prioritize messages ? Summarize the salient aspects .
CoAP itself does not provide a way to prioritize messages . Does it provide the ability to synchronize time ? Summarize the salient aspects .
No , CoAP does not provide a way to synchronize time between clients and servers . Does it provide mechanisms for message security ? Summarize the salient aspects .
CoAP can use Datagram Transport Layer Security ( DTLS ) over UDP to provide message security . CoAP ' s default choice of DTLS parameters is equivalent to 3072-bit RSA keys , yet still it runs well on the smallest nodes .
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