WirelessHART Fieldgate SWG70 Function and system design
Endress + Hauser 13
3.2 WirelessHART network
Fieldgate SWG70 is the master device in the WirelessHART network. Acting as network
manager, it recognizes other devices wanting to join the network. It makes contact with each
in turn and initiates the procedures required for them to join. The network organizes itself
without any intervention on the part of the user. Fieldgate SWG70 also acts as security man-
ager and collects the data sent by the network participants, converting it into a form which
can be used by other systems connected to it.
3.2.1 Network management
In its role as network manager, Fieldgate SWG70 organizes the wireless communication
between the WirelessHART field devices.
Fig. 3-2: Network management
After the Fieldgate has started up the network, devices can join. To this end, it first sends out
a call for devices to join the network. Then, the device sends a join request to announce its
wish 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 Fieldgate, the field device is autho-
rized to join the network. Otherwise, the field device will be rejected.
In the next step, the WirelessHART Fieldgate sends session and network keys as well as
scheduling and routing information to the field device. The field device is told how to partic-
ipate in the network and receives various information from the WirelessHART Fieldgate:
• 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 WirelessHART device or adapter 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 man-
ager informs other WirelessHART field devices when to repeat messages.
3.2.2 WirelessHART security management
Fieldgate SWG70 also acts as security manager. To make communication safe, all messages
are encrypted with industry-standard AES-128 block ciphers with symmetric keys. There-
fore, messages are unreadable for external listeners. The encryption keys are distributed by
the security manager.
The Join Key is used to join the network. Subsequently, the Join Key is automatically
exchanged against the Session Key and the Network Key, i.e. two new additional keys.
1 Step 1: Advertising
2 Step 2: Join Request
3 Step 3: Authorization, Session & Network Keys,
Scheduling and Routing
4 WirelessHART gateway (Fieldgate SWG70)
5 WirelessHART device or adapter
1
2
4
5
3
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