Echelon OpenLNS Commissioning Tool - Manual (Page 135)

OpenLNS CT User’s Guide 119
network overhead for large multicast fan-out connections. For example, a repeated message with
three retries to 64 devices generates 4 packets on the network, whereas an acknowledged message
requires at least 65 packets
• Unacknowledged. 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 significantly more 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. Message packets travel from the sending device to the destination
device using the 2-byte logical address of the destination device.
• Broadcast addressing. 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. 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. 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
OpenLNS CT 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.
Connection Description
Smart
Connection
Description
(SCD)*
Messaging
Service Multicast
Addressing Mode
Acknowledged Acknowledged Group
Acknowledged with Alias Multicast Acknowledged Alias
ConnectDescTemplate_0** N/A N/A
Repeated*** Repeated Group