Iot sdk thesis

 

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2.4
 
Constrained Application Protocol (CoAP) 
Constrained Application Protocol is a web-transfer protocol specially designed for 
constrained (in power, bandwidth, processing power) nodes and networks [10]. CoAP was 
developed by Internet Engineering Task Force (IETF) and has been defined in RFC7252 [22].
For IoT to be truly penetrable to the remotest of the locations, where continuous or 
stable power cannot be guaranteed, the nodes to be deployed are expected to make parsimonious 
use of resources available. The nodes usually have microcontrollers with low processing power, 
small amount of ROM and RAM and they are networked with lossy protocols such as IPv6 over 
Low -Power Wireless Personal Area Networks (6LoWPAN). In a resource-constrained 
environment like such, popular web-transfer protocols such as HTTP are too heavy. So, as a 
remedy, IETF conceived a lighter web-transfer protocol: CoAP [21] 
2.4.1_Abstract_Layering_of_CoAP'>Figure 2.4.1 Abstract Layering of CoAP 
As seen in Figure 2.4.1, CoAP can be represented in a layered abstraction on top of 
UDP. Request response and messages are the features of CoAP headers and they are carried as 
a UDP payload to the destination port specified in the relevant UDP field. 
2.4.1
 
Messaging Model of CoAP 
CoAP supports the request/response model under REST paradigm. This makes it easier 
for the developers to move from the heavier HTTP to the lighter CoAP without having to 
overhaul the transfer architecture significantly. Like HTTP, the CoAP requests are made to the 
server to request an action on a resource (identified by a URI) residing on the server. Server 
responds to the request with a response code. The client requests are made with a method code 
(GET, POST, PUT, DELETE). (Check Annex for Method Codes and Response Codes details). 
The messaging model is based on the information exchange between the UDP endpoints. CoAP 
payloads can be of JSON, XML, CBOR, EXI or even plaintext format.
CoAP offers four types of messages: