User's Manual

Functional description 339
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. Nortel 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 an offline list (also known as
a black list) the polling interval is not disturbed by repeated timeouts of
some slaves.
The controlling station stops polling when data is waiting to be sent to one
of the slaves, or when a slave has indicated that data is ready to send.
The controlling station stops polling when a message request is received
from the eKERNEL. The controlling station then creates a data block and
sends this to the appropriate slave address. A slave station sends data
in the same fashion, but with one difference: the slave first has to wait to
be polled to tell the controlling station that data is ready to send. When a
slave is polled and has data to send, the slave tells the controlling station
to stop polling. The controlling station accepts this request by sending
an ACK to the slave that wants to send data. When it receives an ACK
Nortel Communication Server 1000
DECT Messenger Installation and Commissioning — Book 1
NN43120-301 02.01 4 June 2010
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