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Product Specifications
2. Step 2: joining
3. Step 3: scheduling
4. WirelessHART gateway
5. WirelessHART field device
First, the network manager sends advertising messages to announce the network
’
s existence.
When a WirelessHART field device receives such an advertising message, it tries to join the
network. If the WirelessHART field device can identify itself with the same network ID and join
key as stored in the WirelessHART gateway, the field device is allowed to join the network.
Otherwise, the field device will be rejected.
The network manager can also instruct already joined devices to advertise on its behalf.
In the next step, the network manager sends scheduling information to the field device. The
field device is told how to participate in the network and receives various information from the
WirelessHART gateway:
■
Number and identity of neighboring WirelessHART field devices,
■
When to send messages and which channels to use,
■
When to repeat messages for other WirelessHART field devices,
■
The optimal communication path for messages as well as alternative communication
paths in case of failure.
During this process, the field device may also apply to send messages in certain intervals and
ask the network manager for the appropriate resources. The network manager then takes care
that these resources are available. For example, the network manager informs other
WirelessHART field devices when to repeat messages.
2.1.2
Security Management
The security manager is part of the WirelessHART gateway. To make communication safe, all
messages are encrypted with industry-standard AES-128 block ciphers with symmetric keys.
Therefore, messages are unreadable for external listeners.
The security manager distributes the encryption keys and changes them in certain (random)
intervals, as an option.
2.1.3
Virtual Remote I/O system
The WirelessHART gateway makes wireless communication accessible to host systems
capable of HART technology through the following principles.
WirelessHART devices and wired devices connected to a WirelessHART adapter are made
available to host systems via a virtual HART I/O system. This I/O system contains one or
multiple I/O cards. Each I/O card has up to 2 channels. To each channel, up to 6 wired field
devices may be connected in multi-drop mode. see Figure 2.2 on page 11
The WirelessHART gateway assigns a virtual I/O card to each WirelessHART device and
stores card and channel values in a list. The I/O cards are assigned to the WirelessHART
devices in chronological order (0 ... 249). New WirelessHART devices in the network are
assigned to the next available I/O card.
WirelessHART devices are always assigned to channel 0 of an I/O card. All wired devices
connected to a WirelessHART adapter are always assigned to channel 1 of the same I/O card
as the adapter (multi-drop mode).
