User's Manual

eESPA handles only data blocks of type 1, Call to Pager data blocks. If another type of data
block comes in, eESPA reacts by sending an ACK, but the data block is not processed.
Delivery can also fail if a timeout occurs while sending the data block. The temporary master
station, which is always the sending side, expects to receive an ACK within a timeout of
eESPA_Timeout_n seconds. In the event of a timeout on sending a data block, the sending
side tries to re-send the data block. This retry is attempted x times (where x is the defined value
of the field eESPA_NAK_retry_cnt_n in the eESPA table). After retrying x times and not
receiving an ACK, the temporary master station decides that the transaction is unsuccessful.
Figure 74: msgrpy message NACK
Data flow
The ESPA4.4.4 protocol prescribes a controlling station that polls devices on the
communication line. Polling means sending out requests for data. The polling device, which is
also called controlling station or master, sends out requests to the other devices available on
the communication line. Every device on the line has a specific address. The characters 0 to
9 are available as addresses. Avaya recommends that you assign the character 1 to the
controlling station. In the field eESPA_Polling_address_list_str of the table eESPA you can
define multiple addresses of slave devices. At least one address (that represents a slave) is
required in this field. Multiple addresses are separated by ^.
For example: the value 2^4^5 in eESPA_Polling_address_list_str defines three slaves that are
polled by the controlling station.
Define a control station by placing eESPA_ControlStation_b in the eESPA table on True.
eESPA_LocalAddress_n and eESPA_ExternalAddress_n must be filled up respectively with
the local address of the module (a controlling station prefers a local address 1), and the address
of an external eESPA module or device, with which the module communicates.
The controlling station polls every address with an enquiry. To extend the example, the
controlling station sends 2ENQ, 4ENQ, and 5ENQ. The field eESPA_Polling_intv_n in the
eESPA table defines the time between sequencing polls.
A slave whose address is polled reacts by replying with either a nothing-to-transmit (EOT), or
an enquiry (<master address>ENQ) that tells the controlling station that this slave wants to
transmit some data. If a slave receives data that is not assigned to the slave address, the slave
ignores the data. If a slave does not respond to an enquiry within eESPA_Timeout_n seconds,
the controlling station places this slave in a special offline list. When polling, the controlling
station reads the offline list to determine if a slave is online or not, before sending an enquiry.
After 60 seconds, the slave is removed from the offline list, and polling to the IP address of the
slave is restarted. If the slave does not react, the slave is put back in the offline list. By using
Module - eESPA
124 DECT Messenger Installation and Commissioning — Book 1 March 2012
Comments? [e-mail]