Iot sdk thesis

 
The meaning of the acronyms appearing in the message header are as follows: 
Field 
Type 
Description 
Ver 
2-bit unsigned integer 
Version:
Indicates the version of the CoAP 
T 
2-bit unsigned integer 
Type:
Defines the message: CON, NON, ACK or 
Reset 
TKL 
4-bit unsigned integer 
Token Length
: Defines the length of ‘Token’ field 
Code 
8-bit unsigned integer 
Defines the class in format “x.yy”, where ‘x’ is a 3-bit 
class indicator and ‘yy’ is the 5-bit detail** 
Message ID 
16-bit unsigned 
integer 
Message ID to detect message duplication 
Table 2.4.2.1 CoAP Message Header Sections 
2.4.3
 
Security in CoAP 
Web-transfer protocols like HTTP are transported over TCP, which is reliable in nature. 
Hence, HTTP can be secured by Transport Layer Security (TLS) encryption as it uses TCP. 

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CoAP messages are placed in UDP as payload. Datagrams in UDP are received out-of-
order and the datagram transport is not reliable. Hence, TLS cannot be used. However, CoAP 
messages is secured by Datagram Transport Layer Security (DTLS) as shown in Figure 2.4.2.2: 
Figure 2.4.2.2 CoAP secured with DTLS 
DTLS is a modified version of TLS to compensate for unreliability of UDP-based 
communication. DTLS has been explained in detail in section 2.5. 
2.4.4
 
CoAP v/s HTTP 
HTTP has been designed and revived with resource-abundant Internet devices in mind. 
HTTP typically is network over IP. It requires the reliable transport of TCP for successful 
operation. So, the overhead of HTTP support is too heavy for resource-constraint devices. 
On the other hand, CoAP, by definition, provides an application protocol for resource-
constrained devices. It can work seamlessly over IP or 6LoWPAN at network layer. Most 
importantly, CoAP messages can be transported as UDP payloads, which can make low-latency 
requirements more feasible to achieve.
Hence, CoAP is more suitable for a project in IoT domain such as this thesis.

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