Echelon LNS - Manual (Page 190)

LNS Programmer's Guide 176
allocate a logical address, compute routing tables, and calculate connection timers for the
device. When the device is commissioned, the LNS Object Server will verify, as best it
can, that the device is indeed attached to the expected channel. If it is not, an exception
will be thrown.
When devices are being added to the LNS database as they are discovered (automatic
installation), or as they are physically installed (ad hoc installation), LNS will
automatically determine the device’s channel using the channel isolation process
described in the next section. If the system exclusively uses configured routers, LNS can
always determine the device’s channel.
If LNS cannot uniquely determine a device’s channel, it will use one of the possible
channels as the channel when commissioning the device. If the system uses repeaters or
permanent bridges, your application should always specify the Channel to use when you
create each AppDevice object, since the channel reported by the LNS Object Server may
be incorrect.
Channel Isolation Process
When you add a device to the LNS database, LNS uses the channel isolation process to
determine the channel the device should use, or to validate that the channel you have
assigned to the device is valid.
All router types other than repeaters perform address translation on messages with a
source subnet equal to 0, translating the source subnet to be the subnet of the router side
that first receives the message. The channel isolation process takes advantage of router
source address translation by examining the translated source subnet, and thus
identifies the source channel. In some cases LNS may have to temporarily place the
device in the unconfigured state in order to perform channel isolation.
LNS can only isolate down to a logical channel segment when routers configured as
repeaters or permanent bridges are used. A logical channel segment is a set of channels
connected to each other by routers configured as repeaters or permanent bridges. This is
because:
• Repeaters do not perform source translation.
• Subnets may legally span permanent bridges.
In both cases, it is not possible for LNS to determine which router within the logical
channel segment received a packet first. Installing a device on the wrong channel, but on
the correct channel segment, may have negative consequences. Routing will not be
affected, but LNS may calculate the layer 4 timers incorrectly, which could result in
unnecessary retries or message failures. As a result, Echelon recommends the use of
configured routers, as LNS will always be able to identify the correct channel when
configured routers are used. If this is not possible, the installer should make sure to
install each device on the correct channel, or use the PreMove() and PostMove()
methods to move any devices to their correct channel.
Note that if you are running a remote Full client application that is on a logical channel
segment containing routers of class lcaRepeater, lcaPermanentRepeater or
lcaPermanentBridge, you will need to set the RemoteChannel property prior to
opening the system to specify the channel the client is using.