A Practical Guide to Using the Industrial Internet Connectivity Framework
syntactic interoperability. We examine it
nonetheless because it has wide awareness.
sources, sinks and networks. The databus
can control Quality of Service (QoS) like
update rate, reliability and guaranteed
notification of data liveliness. It can look at
the data inside the updates and optimize
how to send them, or decide not to send
them at all. It also can discover and secure
data flows dynamically. All of these things
define interaction between software
modules. The data-centric paradigm thus
enables software integration.
DDS
Here are five questions to answer to decide
if you need DDS:
1. Is it a big problem if your system goes
down for a short time?
2. Are milliseconds important in your
communications?
3. Do you have more than 10 software
engineers?
4. Are you sending data to many places, as
opposed to just one (like to the cloud or
a database)?
5. Are you implementing a new IIoT
architecture?
So how does this satisfy the five questions?
1. Since it is directly controlling flow, a
databus does not require servers. So,
there’s no single point of failure. The
downtime required to reboot a server
and remake connections unexpectedly is
never necessary. Without direct
relationships with peers, redundancy is
transparent. If the application is
managing a thermostat, optimizing a
plant, or assembling parts, a short
downtime is not catastrophic. However,
if the software is responsible for
someone’s breathing or the stability of
the power grid, even short interruptions
cannot be tolerated.
2. Since the databus has full control over
how data flows, it can send information
directly between peers. Thus, it can
deliver in times measured in milliseconds
or microseconds. DDS can use multicast
intelligently when available. It knows
delivery deadline requirements and can
measure if the system is meeting
delivery times. So, it can warn
applications if the network (or anything
else) cannot handle the needed flow
rates.
If you answered three out of the five
questions “yes,” you probably should use
DDS.
DDS is a series of standards managed by the
OMG that define a databus. A databus is
data-centric information flow control. It’s a
similar concept to a database, which is data-
centric information storage. The key
difference: a database searches old
information by relating properties of stored
data. A databus finds future information by
filtering properties of the incoming data.
Both understand the data contents and let
applications act directly on and through the
data rather than with each other.
Applications using a database or a databus
do not have a direct relationship with peer
applications.
The databus uses knowledge of the
structure, contents and demands on data to
manage dataflow. It can, for instance,
resolve redundancy to support multiple
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September 2017