Echelon LonBridg Server - Manual (Page 27)

LonBridge Server User’s Guide 21
The LonBridge Server reads the LonBridge configuration file to determine the
name of the network interface (such as LON1) for a layer-5 MIP interface, or the
serial device name (such as /dev/ttyS0) for a ShortStack interface. The
LonBridge Server cannot share a network interface with other applications. If
the network interface is already in use by another application, the LonBridge
Server waits for the network interface to become available.
The LonBridge Server discovers ISI devices, and for each discovered device
searches for a device class file with a matching program ID.
The LonBridge Server includes an ISI domain address server (DAS). The domain
address server coordinates assignment of unique domain IDs and maintains and
distributes an estimate of network size to optimize use of available channel
bandwidth. The domain address server broadcasts timing guidance messages
that provide an estimate of network size and topology as defined by the ISI
Protocol Specification .
Discovering Devices
The LonBridge Server discovers devices in a L ON W ORKS network and maintains
a table of all discovered devices. Properties for each device include the device
name, program ID, network variables, and network variable fields. The
LonBridge Server supports up to 200 devices.
The LonBridge Server can discover devices using either (or both) of the following
methods:
•
ISI Device Discovery : The LonBridge Server discovers ISI devices using
periodic messages sent by all ISI devices called device resource usage
messages (DRUMs). The DRUM is a periodic message sent by every ISI
device containing the device’s Neuron ID and logical network address.
Devices can change their logical network address at any time, and report the
changed address through an updated DRUM. The LonBridge Server updates
device address information when a change is reported by a DRUM.
When the LonBridge Server receives a DRUM with a Neuron ID that it has
not previously discovered, it reads the program ID from the device and
searches for a matching device class file. If the LonBridge Server finds a
matching device class file, it adds the device to a local device table that serves
as a cache for all discovered devices.
• Broadcast Device Discovery : The LonBridge API provides a function to
discover all devices in a network. This function provides accelerated device
discovery, but increases network usage for a short period. The LonBridge
Server can discover all unconfigured devices and all devices within a specified
domain. As with ISI device discovery, only devices with matching device
class files are discovered.
Monitoring and Polling a Network Variable
Based on properties defined in the device class files, the LonBridge Server
monitors specified network variables on all devices in the device table, and
reports value changes to LonBridge applications. For layer-5 MIP devices, each
device can have up to up to 4096 network variables. For ShortStack devices,
each device can have up to up to 254 network variables.