mjCoAP: An Open-Source Lightweight Java CoAP Library for Internet of Things Applications - Interoperability and Open-Source Solutions for the Internet of Things - page 117

interface and sensors/actuators. The limitations of smart objects are not just
hardware-related. In order to achieve energy eciency, communication protocols
and operating systems/software must be properly designed and implemented in
order to minimize energy consumption. Smart objects operate in low-power and
lossy networks (LLNs), which make use of wireless communication protocols,
such as IEEE 802.15.4.
The Internet Protocol (IP) has been envisaged to be the true enabler for a
global IoT. An IP-based IoT would seamlessly integrate and interact with the
traditional Internet, forming the so-called “ extended Internet .” As billions of smart
objects are expected to be deployed and due to IPv4 address depletion, IPv6 has
been identified as the perfect candidate to be the lingua franca of the IoT.
Due to the diverse nature of devices, in order to guarantee true and effec-
tive interoperability, standard communication protocols must be adopted, based
on the IP stack. Bringing IP to smart objects has been and still is the focus
of many standardization organizations, such as the Internet Engineering Task
Force (IETF) and the International Telecommunication Union Telecommunica-
tion Standardization Bureau (ITU-T), and research projects, such as the FP7
EU project CALIPSO [ 1 ].
The IETF Constrained RESTful Environments (CoRE) [ 2 ] Working Group is
chartered to provide a framework for resource-oriented applications running on
constrained IP networks. The Constrained Application Protocol (CoAP) [ 3 ]has
been designed to be standard application-layer protocol for bringing the REpre-
sentational State Transfer (REST) [ 4 ] paradigm, originally conceived for HTTP-
based applications [ 5 ], to constrained IoT applications. CoAP is an UDP-based
lightweight binary protocol based on a request/response communication model,
which maps to HTTP for integration with the Web. CoAP meets constrained
application requirements, such as very low overhead and supports multicast com-
munications. Depending on the specific scenario, other application-layer proto-
cols may be considered for IoT applications. Indeed, there are two paradigms that
can be adopted for communication between application: (i) request/response
(polling) and (ii) publish/subscribe (push-based). In the former, a client node
explicitly requests some information to a server node, which replies with the
requested information. In the latter, a node publishes content, which is subse-
quently delivered to one or more subscribers, through a broker or directly. CoAP
and HTTP implement a polling model, while other protocols such as MQTT [ 6 ]
and AMQP [ 7 ] implement a push-based communication model. CoAP also sup-
ports resource observation, through a specifically designed option, which allows
a client node to request a resource and receive notifications upon resource state
changes in subsequent responses. The FP7 EU project IoT6 [ 8 ] aims at overcom-
ing the fragmentation of IoT by exploiting standard communication protocols
(6LoWPAN, CoAP).
Other interoperability efforts are being currently investigated, such as the
possibility to provide application frameworks for the management of IoT data.
The FP7 EU project OpenIoT [ 9 ] is chartered to provide an open source