The
probability A of having an erroneous CoAP packet at the application layer
including the retransmission at MAC layer is derived as A
. Here, r is the maximum
number of retransmission allowed for the MAC layer (default value is 5).
However, the entire IEEE 802.15.4 MTU is 127bytes. Hence, the CoAP packet
should be fragmented. If a CoAP message is comprised of f fragments, the
probability
of having an erroneous fragment of a CoAP message
is given by: