Echelon FTXL - Manual (Page 56)

44 Creating a Model File
Legacy Neuron C Constructs
You must use the Neuron C Version 2.1 syntax described in this manual. You
cannot use legacy Neuron C constructs for defining L ON M ARK -compliant
interfaces. That is, you cannot use the config modifier for network variables, and
you cannot use Neuron C legacy syntax for declaring functional blocks or
configuration properties. The legacy syntax used an sd_string() modifier
containing a string that starts with a ‘&’ or ‘@’ character.
Using Authentication for Network Variables
Authentication is a special acknowledged service between one source device and
one or more (up to 63) destination devices. Authentication is used by the
destination devices to verify the identity of the source device. This type of service
is useful, for example, if a device containing an electronic lock receives a message
to open the lock. By using authentication, the electronic lock device can verify
that the “open” message comes from the owner, not from someone attempting to
break into the system.
Authentication doubles the number of messages per transaction. An
acknowledged message normally requires two messages: an update and an
acknowledgment. An authenticated message requires four messages, as shown
in Figure 8 on page 46. These extra messages can affect system response time
and capacity.
A device can use authentication with acknowledged updates or network variable
polls. However, a device cannot use authentication with unacknowledged or
repeated updates.
For a program to use authenticated network variables or send authenticated
messages, you must perform the following steps:
1. Declare the network variable as authenticated, or allow the network
management tool to specify that the network variable is to be
authenticated.
2. Specify the authentication key to be used for this device using a network
management tool, and enable authentication. You can use the LonMaker
Integration Tool to install a key during network integration, or your
application can use the LonQueryDomainConfig() and
LonUpdateDomainConfig() API functions to install a key locally.
Specifying the Authentication Key
All devices that read or write a given authenticated network variable connection
must have the same authentication key. This 48-bit authentication key is used
in a special way for authentication, as described in
How Authentication Works on
page 45. If a device belongs to more than one domain, you must specify a
separate key for each domain.
The key itself is transmitted to the device only during the initial configuration.
All subsequent changes to the key do not involve sending it over the network.
The network management tool can modify a device’s key over the network, in a
secure fashion, with a network management message.