Operating instructions

3 Function and System Design WirelessHART Fieldgate SWG70

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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 manager 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 gateway, the field device is authorized to join the network.

Otherwise, the field device will be rejected.

In the next step, the WirelessHART gateway sends session and network keys as well as scheduling

and routing 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 neighbouring 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 manager informs other

WirelessHART field devices when to repeat messages.

3.2.2 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. Therefore, 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 4 WirelessHART gateway (Fieldgate SWG70)

2 Step 2: Join Request 5 WirelessHART device or adapter

3 Step 3: Authorization, Session & Network

Keys, Scheduling and Routing