Echelon LonMaker - Manual (Page 135)

LonMaker User’s Guide 119
notified when an update fails, but it is up to the developer of the sending device to handle the
notification in the device application. While acknowledged service is very reliable, it can create
excessive message traffic, especially for large fan-out or polled fan-in connections. When
acknowledged messaging is used, every receiving device has to return an acknowledgment.
Acknowledged messaging can be used with up to 63 receiving devices, but an acknowledged
message to 63 devices generates at least 63 acknowledgements—more if any retries are required
due to lost acknowledgements.
• Repeated means that the sending device sends out a series of network variable updates, but does
not expect any confirmation from the receiving device. Repeated service with three repeats has a
99.999% success rate in delivering messages. Repeated service provides the same probability of
message delivery as acknowledged messaging with the same number of retries, with significantly
lower network overhead for large multicast fan-out connections. For example, a repeated message
with three retries to 64 devices generates four packets on the network, whereas an acknowledged
message requires at least 64 packets
• Unacknowledged means that the sending device sends out the network variable update only once
and does not expect any confirmation from the receiving device. This message service type
consumes the least amount of resources, but is the least reliable.
You can enable authentication for any acknowledged connection. With authentication, the receiving
device challenges the sending device for verification in between receiving the network variable update
and sending an acknowledgement to the sending device. This results in twice as much traffic as
acknowledged service. .
You can enable priority messaging for any connection. With priority messaging, the device with the
highest priority sends its packet before any other devices can send theirs. This is accomplished by
assigning each priority device a time slot where it can transmit before all other lower priority and
non-priority devices. These time slots consume network bandwidth; therefore, priority messaging
should only be used for critical devices and data.
Addressing Mode
You can specify the addressing mode for each connection description. The addressing mode specifies
the type of destination addressed that is used for packets within the connection. Addressing modes
include subnet/node ID for unicast connections, and broadcast, group, or alias for multicast (fan-out)
connections. Each of these addressing modes is described as follows:
• Subnet/Node ID addressing means that a message packet travels from the sending device to the
destination device using the 2-byte logical address of the destination device.
• Broadcast addressing means that message packets are sent to all devices within a domain (all
devices in a network) or a subnet (a set of devices on one channel or a set of channels connected
by permanent repeaters).
• Group addressing means that message packets are sent to devices assigned to a group, which
requires a 1-byte address shared by all members of the group.
• Alias addressing means that message packets are sent to devices using network variable aliases
and unicast addressing, if possible. Aliases behave like shadow copies of network variables and
can be used to overcome connection limitations of non-alias network variables.
Subnet/node ID and broadcast addressing do not require an address table entry on the destination
device or devices, whereas group addressing does. Alias addressing requires an address table entry on
the destination device when used with group addressing.
Viewing and Creating Connection Descriptions
The LonMaker tool provides fifteen pre-defined connection descriptions, which vary in the message
service type and addressing mode used. The following table details each of these pre-defined
connection descriptions.