Mailbox Structure

Owned by Matthias Kassner
11-Jul-2024
2 min read

SMART ACK Mailboxes store the entire radio telegram which will be transmitted as Data Acknowledge telegram to the SMART ACK Sensor upon a SMART ACK Reclaim request. Data Acknowledge telegrams contain the destination address of the SMART ACK Sensor and therefore use the format of the ERP1 Addressed Data Telegram. This telegram has the following structure:

image-20240711-124602.png
SMART ACK Data Acknowledge Telegram

The size of the SMART ACK Mailbox in ERP1 is therefore the maximum size of an ERP1 Addressed Data Telegram which is 21 byte (when using 9 byte of payload).

The equivalent size of an ERP2 telegram with the same payload size is 23 byte; therefore the size of SMART ACK Mailboxes for ERP2 is 23 byte.

Note that the current SMART ACK specification does not support telegram chaining. Therefore it is not possible to use SMART ACK for most secure telegram types as Sequence Counter and Authentication Signature will be part of the payload and thereby severely limit the available payload size for data telegrams (1 byte of available payload for the case Sequence Counter = 4 byte and Authentication Signature = 4 byte).

Mailbox Identification

Mailboxes are identified at the Postmaster using the following two parameters:

  • SMART ACK Sensor EURID
    This is the EnOcean source address of the SMART ACK Sensor.

  • Mailbox Index
    If a SMART ACK Sensor communicates with more than one SMART ACK Controller via the same SMART ACK Repeater, then the Mailbox Index will distinguish between different Mailboxes at the same SMART ACK Repeater holding telegrams to the same SMART ACK Sensor.
    The Mailbox Index is 0 for the common case that a SMART ACK Sensor communicated with only one SMART ACK Controller.