3 Engineering IoT Networks
113
at each node, which makes it transition/edge-triggered instead of voltage/leveltriggered. Special hardware is required to connect Modbus Plus to a computer,
typically a card made for the ISA, PCI or PCMCIA bus.
• Modbus TCP/IP or Modbus TCP It is a Modbus variant used for communications over TCP/IP networks, connecting over port 502. It does not require a
checksum calculation, as lower layers already provide checksum protection.
• Modbus over TCP/IP or Modbus over TCP or Modbus RTU/IP. It is a
Modbus variant that differs from Modbus TCP in that a checksum is included
in the payload as with Modbus RTU.
• Modbus over UDP Some have experimented with using Modbus over UDP on
IP networks, which removes the overheads required for TCP.
The last three variants were developed to take advantage of the benefits of the
TCP/IP architecture over Ethernet networks. The IP layer provides addresses and
routing functionality, and Ethernet implements medium access control and physical
transmission.
The core part of all Modbus messages contains a device identifier as destination
address, a function code (basically to denote read or write operations), and a data
field to handle data or command values. Depending on the specific Modbus variant,
such fields are preceeded and followed by delimiters and an error checking field.
3.3.2 Near-Field Communication (NFC)
Near-field communication (NFC) is a set of communication protocols that enable
two electronic devices to establish communication by bringing them within 4 cm
(1.6 in) of each other. This is sometimes referred to as NFC/CTLS (Contactless) or
CTLS NFC [19, 20]. The standardization body is NFC Forum.
NFC devices are used in contactless payment systems, similar to those used in
credit cards and electronic ticket smartcards and allow mobile payment to replace
or supplement these systems. NFC-enabled devices can act as electronic identity
documents and key cards. NFC is also used for social networking, for sharing
contacts and small files. Even if NFC offers a low-speed connection, its setup is
simple, and it can be used to bootstrap more capable wireless connections.
NFC is a particular case of radio-frequency identification (RFID) technology
which employs short-range electromagnetic induction between two loop antennas
as a communication channel. NFC operates within the globally available unlicensed
radio-frequency ISM band of 13.56 MHz on ISO/IEC 18000-3 air interface at rates
ranging from 106 to 424 kb/s. NFC always involves an initiator and a target; the
initiator actively generates an RF field that can power a passive target. This enables
NFC targets to take very simple form factors such as unpowered tags, stickers,
key fobs, or cards. NFC peer-to-peer communication is possible, provided both
devices are powered. Secure communications are available by applying encryption
algorithms as is done for credit cards.
113
at each node, which makes it transition/edge-triggered instead of voltage/leveltriggered. Special hardware is required to connect Modbus Plus to a computer,
typically a card made for the ISA, PCI or PCMCIA bus.
• Modbus TCP/IP or Modbus TCP It is a Modbus variant used for communications over TCP/IP networks, connecting over port 502. It does not require a
checksum calculation, as lower layers already provide checksum protection.
• Modbus over TCP/IP or Modbus over TCP or Modbus RTU/IP. It is a
Modbus variant that differs from Modbus TCP in that a checksum is included
in the payload as with Modbus RTU.
• Modbus over UDP Some have experimented with using Modbus over UDP on
IP networks, which removes the overheads required for TCP.
The last three variants were developed to take advantage of the benefits of the
TCP/IP architecture over Ethernet networks. The IP layer provides addresses and
routing functionality, and Ethernet implements medium access control and physical
transmission.
The core part of all Modbus messages contains a device identifier as destination
address, a function code (basically to denote read or write operations), and a data
field to handle data or command values. Depending on the specific Modbus variant,
such fields are preceeded and followed by delimiters and an error checking field.
3.3.2 Near-Field Communication (NFC)
Near-field communication (NFC) is a set of communication protocols that enable
two electronic devices to establish communication by bringing them within 4 cm
(1.6 in) of each other. This is sometimes referred to as NFC/CTLS (Contactless) or
CTLS NFC [19, 20]. The standardization body is NFC Forum.
NFC devices are used in contactless payment systems, similar to those used in
credit cards and electronic ticket smartcards and allow mobile payment to replace
or supplement these systems. NFC-enabled devices can act as electronic identity
documents and key cards. NFC is also used for social networking, for sharing
contacts and small files. Even if NFC offers a low-speed connection, its setup is
simple, and it can be used to bootstrap more capable wireless connections.
NFC is a particular case of radio-frequency identification (RFID) technology
which employs short-range electromagnetic induction between two loop antennas
as a communication channel. NFC operates within the globally available unlicensed
radio-frequency ISM band of 13.56 MHz on ISO/IEC 18000-3 air interface at rates
ranging from 106 to 424 kb/s. NFC always involves an initiator and a target; the
initiator actively generates an RF field that can power a passive target. This enables
NFC targets to take very simple form factors such as unpowered tags, stickers,
key fobs, or cards. NFC peer-to-peer communication is possible, provided both
devices are powered. Secure communications are available by applying encryption
algorithms as is done for credit cards.