Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
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Multipoint Polling
Multipoint Polling
When a multipoint supervisor application is not sending receiving frames, it can cause
EnvoyACP/XF to poll all tributary stations specified in the DEFINELIST station list to
determine whether any tributary has data to transmit.
The auto-poll feature of EnvoyACP/XF systematically transmits a poll frame (RR,P) to
each tributary station in the DEFINELIST station list and checks for a response.
Once the application issues a READ to initiate polling, EnvoyACP/XF performs auto-
polling in either of the following ways:
Polling List
The supervisor application uses the DEFINELIST procedure (described in the
DEFINELIST Procedure on page 4-6) to create a station list containing the addresses of
all stations to be polled, then issues a READ request to initiate polling. At this point,
EnvoyACP/XF uses the series of four-word blocks in the station list to create a polling
list. EnvoyACP/XF copies the polling list into memory for future use. For each entry,
this polling list includes the following:
•
Fixed 4-octet address field
•
2-octet control field
•
2-octet response compare field
From the address and control fields, EnvoyACP/XF builds a frame for each entry, then
transmits these frames one at a time and checks responses against the associated
response-compare fields in the polling list.
Responses to a Poll
If the response does not contain the proper station identification in the address field, the
READ request completes and the auto-poll sequence terminates.
Continuous
polling
EnvoyACP/XF continuously loops through the station list without
notifying the application. When EnvoyACP/XF reaches the end of the
station list, it loops back to the top of the list.
Polling continues until a tributary responds with data, until a timeout
occurs (that is, a tributary does not respond at all), or until an error
condition aborts polling.
Limited
polling
EnvoyACP/XF continuously loops through the station list; however,
EnvoyACP/XF notifies the user application when EnvoyACP/XF has
completed the specified cycles through the station list. (The associated
READ call completes with condition code CCG and file-system error
176, “poll sequence ended without a responder.”)
When EnvoyACP/XF reaches the end of the station list, it loops back to
the top of the list (if there are more cycles). Polling continues until a
tributary responds with data, until a timeout occurs (that is, a tributary
does not respond at all), or until an error condition aborts polling.