exPL Examples

Example Communications Exchanges

Example: New sensor start up

  • Complete network layer address assignment process for network type
  • Standard xPL start up procedures apply
    • Broadcast xPL heartbeat with source device address
    • May get configuration from xPL DCM
    • ....
  • Other xPL applications learn of the device from the xPL heartbeats

Example: High speed xPL device polling a low speed sensor

  • xPL poll command is broadcast on a high speed network
  • Low speed gateway (Ethernet to point-2-point) hears the broadcast and filters the message based on table of learned device classes and learned device addresses on the low speed side. The target matching in the table is the same as the target matching ultimately used by the xPL end device. The low speed gateway attempts a unicast delivery by looking up the target in the table of learned devices. If no matching targets are found then the message will be dropped. If more than one xPL device matches the target then the network implementation may choose to send multiple unicast messages or may choose to send a broadcast message.
  • Low speed sensor hears the unicast or broadcast message the target of which matches the sensor's address / message class.
  • Low speed sensor sends a unicast response back to the originating network address.
  • Low speed gateway broadcasts the message onto the high speed network.

Example: Low speed sensor sends xPL trigger message

Low speed sensors have two choices when sending messages. The messages can be sent to the network layer broadcast address honoring the xPL specification, however this method may cause congestion in mesh type networks. The messages can also be unicast to a low speed gateway. There are two design challenges with this second approach. One is that the other xPL devices on the same low speed network will not hear the unicast message. The low speed gateway must use the same target matching and filtering to decide if the message should be retransmitted back onto the low speed network. Another design challenge is that the low speed xPL device must decide where to send the unicast messages. A method must be introduced that allows the xPL low speed device to determine the address of the xPL low speed gateway.
  • xPL low speed gateway sends heartbeats indicating it is a low speed gateway
  • xPL low speed device unicasts the xPL trigger message. The xPL target is * as required by the xPL specification.
  • xPL low speed gateway broadcasts message onto high speed network
  • xPL low speed gateway optionally forwards the message on to the same or additional low speed networks after applying the filter criteria and consulting the low speed gateway FIB.


  • Device Address or Device ID - 64bit GUID assigned to the device. Each device is one node on a network. The device may be a member of multiple networks but may only have one instance on each network. In this case the GUID for the device is the same on each network.
  • Network Address - Network unique identifier assigned to the network node. Typically these addresses are dynamically assigned during device commissioning but may be static (e.g. RS485 bus master is always network address 0).

Contributors to this page: michael .
Page last modified on Saturday 19 of November, 2011 13:02:13 CST by michael.