Integration of Iot technologies into the Smart Grid

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Figure 4.
Architecture of the proposed IEC 61850 Web Platform.
The term Web User is used in this paper to refer to a generic application running on a
generic device which consumes the services offered by the IEC 61850 Web Platform. It is
constrained neither to be IEC 61850 compliant nor to implement the IEC 61850 communica-
tion stack. The only constraints are the adoption of RESTful-based communication and the
MQTT-based exchange of information.
The RESTful Web Service Interface shown by Figure
4
accepts requests submitted by a
registered and authenticated Web User.
The Middleware module inside the IEC 61850 Web Platform performs all the opera-
tions needed to fulfil each request coming from a Web User. These requests may require data
exchange with the available IEC 61850 Servers; for this reason, the Middleware includes an
IEC 61850 Client used for the access to the IEC 61850 Servers. Communication between
an IEC 61850 Client and IEC 61850 Servers occurs according to the standard IEC 61850
communication protocol and services (i.e., using the IEC 61850 communication stack) [
15
].
The Middleware includes a particular module named MQTT Publisher, which is in charge
of publishing information taken from the IEC 61850 Server, through an MQTT Broker, using
the MQTT protocol. The Middleware is made up of a local repository shown by Figure
4
(i.e., Local SCL Repository), used to store ICD files containing the SCL description of the
data model maintained by each IEC 61850 Server involved in the data exchanges with Web
Users. This description is needed by the IEC 61850 Web Platform to accomplish the services
offered, as explained in the remainder of this section. The use of this local repository is not
mandatory, but it is very useful because it avoids remote queries to the IEC 61850 Server
when information about the SCL description of the relevant data model is needed.
Communication between a Web User and the IEC 61850 Web Platform may be
synchronous (based on RESTful web services) or asynchronous (based on MQTT Pub-
lish/Subscribe Pattern), as shown in Figure
4
.
The Web User uses synchronous communication to interact with the Web Service In-
terface to request one of the services offered by the IEC 61850 Web Platform. POST requests
are realized using the JSON format. For each Web User’s request through the RESTful Web
Service Interface, the IEC 61850 Web Platform will send a relevant response. Each Web
User needing to use the IEC 61850 Web Platform through synchronous communication
must be previously registered (by user credentials in terms of username and password)
and authenticated (through the use of a signed token which is held by the Web User).
Asynchronous communication is realized through the use of MQTT Brokers to allow
the Web User to receive data produced by the platform; data is mainly originated by the
IEC 61850 Servers. The Web User must be registered to a particular topic in order to receive
the information needed from the relevant MQTT Broker. The Broker may be chosen by the
Web User, or he can use a given predefined Broker.
The following subsections provide more details about the IEC 61850 Web Platform. In
particular, all the operations performed by the Middleware and its internal components are

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pointed out; the authors preferred to detail the functionalities of the Middleware for each
single service offered by the RESTful Web Service Interface and requested by the Web User.
Before this description, Section
4.1
provides an overview of a particular syntax defined to
allow the Web User to univocally identify each element of the IEC 61850 data model.
4.1. Definition of a Syntax for the Web User
In Section
3
, it was noted that each piece of information in the IEC 61850 Server is
maintained according to the hierarchical data model structure shown by Figures
1
and
2
; in

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