Envoy Application Programming Manual

BISYNC Centralized Multipoint Supervisor Protocol
Envoy Application Programming Manual—427159-001
4-26
Line Action by Procedure Call
Line Action by Procedure Call
This subsection describes the BISYNC control sequences transmitted because of calls to
file-system procedures. The actions of file-system procedures in response to line states
and the reception of selected control sequences are also described.
This subsection includes:
•
READ Procedure on page 4-26
•
WRITE Procedure on page 4-30
•
WRITEREAD Procedure (Conversational Exchange) on page 4-33
•
CONTROL Procedure (Send EOT) on page 4-34
•
CONTROL Procedure (Send WACK) on page 4-35
•
CONTROL Procedure (Enable RVI) on page 4-35
•
CONTROL Procedure (Send TTD) on page 4-35
READ Procedure
The READ procedure is used to initiate the polling sequence and to read messages
containing data from a responding tributary station. While messages are being read, the
line is in the READ state. The line returns to the CONTROL state when the tributary
station sends an EOT sequence to indicate the completion of the transmission.
Initial READ (Line in CONTROL State)
An initial READ causes Envoy, on behalf of the application process, to begin polling all
addresses in the poll list (Example 4-7). If a station does not have a message to send, it
responds with an EOT and polling continues with the next station in the poll list. Polling
continues until one of the following happens:
•
A station responds with a message.
•
An error 171 (no response or invalid response received) occurs.
•
The specified number of passes through the poll list have been made.
The successful receipt of the initial message is indicated by a condition code of CCE
upon completion of the READ. Following the receipt of the initial message, the line
goes into a READ state. The address list entry number of the station that responded with
a message is returned in the message control word, bits 8:15.