mjCoAP: An Open-Source Lightweight Java CoAP Library for Internet of Things Applications - Interoperability and Open-Source Solutions for the Internet of Things - page 124

oranumberof MAX RETRANSMIT retransmissions is reached, according to
the CoAP standard; in both cases the user of the Reliable transmission layer
is informed of the result of the transmission, that is whether the message has
been received by the remote entity (confirmed by the ACK ), or a transmission
failure (transmission timeout) has occurred. Similarly, at the server side, the
Reliable transmission is responsible of receiving and processing CON messages
and automatically sending the corresponding ACK messages; according to
RFC 7252, both separate and “piggybacked” responses are supported; in the
latter case, the Reliable transmission layer is also responsible of sending the
piggybacked responses.
- Messaging - It is the sublayer that is responsible for sending and receiving
single CoAP messages, regardless they are requests or responses, CON ,or
NON , ACK ,or RST messages.
Under the Messaging sublayer, there is the standard transport protocol (UDP
or DTLS).
Fig. 1. mjCoAP stack architecture.
The Transact ion layer is implemented by the mjCoAP classes CoapTrans-
actionClient and CoapTransactionServer , and the corresponding listening inter-
faces CoapTransactionClientListener and CoapTransactionServerListener ,used
for intercepting transaction events (e.g. at the client-side, the reception of a
response within a CoAP transaction). The Reliable transmission layer is imple-
mented by the classes CoapReliableTransmission and CoapReliableReception ,
and the listener interface CoapReliableTransmissionListener . Finally, the Mes-
saging layer is implemented by the class CoapProvider and the listening inter-
face CoapProviderListener . Within the Messaging layer, the following classes has
been also defined: (i) CoapMethodId ; (ii) CoapTransactionId and CoapReliable-
TransmissionId , which extend the abstract class CoapId , and that are used for