Echelon LonTal Stack - Manual (Page 86)

74 Creating a Model File
messages and commands be secret, because they are sent unencrypted over the
network, and anyone who is determined can read those messages.
It is good practice to connect a device directly to a network management tool
when initially installing its authentication key. This direct connection prevents
the key from being sent over the network, where it might be detected by an
intruder. After a device has its authentication key, a network management tool
can modify the key, over the network, by sending an increment to be added to the
existing key.
You can update the device’s address without having to update the key, and you
can perform authentication even if the devices’ domains do not match. Thus, a
LonTalk Stack device can set its key during device manufacturing, and you can
then use a network management tool to update the key securely over the
network.
Managing Memory
The LonTalk Interface Developer Neuron C compiler generates four tables that
affect memory usage. The LonTalk host stack and network management tools
use these tables to define the network configuration for a device. The LonTalk
Interface Developer utility allocates space for the following tables:
• Address table
• Alias table
• Domain table
• Network variable configuration table
See the ISO/IEC 14908-1 Control Network Protocol Specification for more
information about these tables. This document is available from ISO:
www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=60203 .
See Appendix E, Determining Memory Usage for LonTalk Stack Applications, for
information about how to calculate the memory requirements for you LonTalk
Stack application.
Address Table
The address table contains the list of network addresses to which the device
sends network variable updates or polls, or sends implicitly-addressed
application messages. You can configure the address table through network
management messages from a network management tool.
By default, the LonTalk Interface Developer utility calculates the size of the
address table. The utility calculates the required number of address table entries
based on parameters defined in the device’s interface, such as the number of
static polling input network variables, static non-constant output network
variables, bindable message tags, the number of aliases, and the number of
dynamic network variables. The utility always allocates at least 15 address table
entries. Within the LonTalk Interface Developer utility, you can override the
automatic calculation of the table size and specify any number of entries, from 0
to 4096.