112
E. Fraccaroli and D. Quaglia
Protocol (either version 4 or version 6) can be used over IEEE 802.15.4, Wi-Fi,
LoRaWAN, and all cellular standards. Some combinations are mandatory (e.g.,
ZigBee or 6LoWPAN over IEEE 802.15.4, ISA100.11a or Thread with UDP), while
others are optional (e.g., IP over LoRaWAN or over cellular networks).
In the rest of the chapter, the standards reported in Fig. 3.8 will be presented in
details, but it is worth referring to Fig. 3.8 to recall their position in the protocol
stack. Standards that cover the Physical Layer fall into two classes depending on
the type of adopted frequency bands, i.e., licensed or unlicensed. Cellular networks
described in Sect. 3.3.17 use licensed frequency bands, while all other standards
adopt unlicensed frequency bands.
3.3 IoT Network Technologies and Standards
3.3.1 Modbus
The Modbus protocol was created in 1979 by Modicon (now Schneider Electric)
to share data between programmable logic controllers (PLCs) [18]. The open and
royalty-free specification of the protocol, along with its simplicity, allowed it to
become the first widely accepted de facto standard for industrial communication.
Modbus enables client/server communication between a master device and many
slave devices connected to the same network, for example, a system that measures
temperature and humidity and communicates the results to a computer. Modbus is
often used to connect a supervisory computer with a remote terminal unit (RTU) in
supervisory control and data acquisition (SCADA) systems. There are many variants
of Modbus protocol:
• Modbus RTU It uses serial communication standards such as RS-232 and RS485. Devices can be connected in a linear tree topology also known as daisy
chain in which each node act as both end node and intermediate system relaying
messages for the other nodes. It uses a compact, binary representation of the data
for protocol communication. The RTU format follows the commands/data with
a cyclic redundancy check checksum as an error check mechanism to ensure the
reliability of data. Modbus RTU is the most common implementation available
for Modbus. A Modbus RTU message must be transmitted continuously without
inter-character hesitations. Modbus messages are separated by idle periods.
• Modbus ASCII It is used in serial communication and makes use of ASCII
characters for protocol communication. The ASCII format uses a longitudinal
redundancy check checksum. Modbus ASCII messages are framed by leading
colon (“:”) and trailing newline (CR/LF).
• Modbus Plus (Modbus+, MB+ or MBP) It is proprietary to Schneider Electric,
and unlike the other variants, it supports peer-to-peer communications between
multiple masters. It requires a dedicated coprocessor to handle fast HDLC-like
token rotation. It uses twisted pair at 1 Mb/s and includes transformer isolation
E. Fraccaroli and D. Quaglia
Protocol (either version 4 or version 6) can be used over IEEE 802.15.4, Wi-Fi,
LoRaWAN, and all cellular standards. Some combinations are mandatory (e.g.,
ZigBee or 6LoWPAN over IEEE 802.15.4, ISA100.11a or Thread with UDP), while
others are optional (e.g., IP over LoRaWAN or over cellular networks).
In the rest of the chapter, the standards reported in Fig. 3.8 will be presented in
details, but it is worth referring to Fig. 3.8 to recall their position in the protocol
stack. Standards that cover the Physical Layer fall into two classes depending on
the type of adopted frequency bands, i.e., licensed or unlicensed. Cellular networks
described in Sect. 3.3.17 use licensed frequency bands, while all other standards
adopt unlicensed frequency bands.
3.3 IoT Network Technologies and Standards
3.3.1 Modbus
The Modbus protocol was created in 1979 by Modicon (now Schneider Electric)
to share data between programmable logic controllers (PLCs) [18]. The open and
royalty-free specification of the protocol, along with its simplicity, allowed it to
become the first widely accepted de facto standard for industrial communication.
Modbus enables client/server communication between a master device and many
slave devices connected to the same network, for example, a system that measures
temperature and humidity and communicates the results to a computer. Modbus is
often used to connect a supervisory computer with a remote terminal unit (RTU) in
supervisory control and data acquisition (SCADA) systems. There are many variants
of Modbus protocol:
• Modbus RTU It uses serial communication standards such as RS-232 and RS485. Devices can be connected in a linear tree topology also known as daisy
chain in which each node act as both end node and intermediate system relaying
messages for the other nodes. It uses a compact, binary representation of the data
for protocol communication. The RTU format follows the commands/data with
a cyclic redundancy check checksum as an error check mechanism to ensure the
reliability of data. Modbus RTU is the most common implementation available
for Modbus. A Modbus RTU message must be transmitted continuously without
inter-character hesitations. Modbus messages are separated by idle periods.
• Modbus ASCII It is used in serial communication and makes use of ASCII
characters for protocol communication. The ASCII format uses a longitudinal
redundancy check checksum. Modbus ASCII messages are framed by leading
colon (“:”) and trailing newline (CR/LF).
• Modbus Plus (Modbus+, MB+ or MBP) It is proprietary to Schneider Electric,
and unlike the other variants, it supports peer-to-peer communications between
multiple masters. It requires a dedicated coprocessor to handle fast HDLC-like
token rotation. It uses twisted pair at 1 Mb/s and includes transformer isolation