Bristol Babcock Network 3000 Setup Manual page 150

Appendix B - Message Traffic
Immediate Response Transactions
The immediate response concept was initially limited to only certain Network 3000-
series devices such as the EGM 3530-10A and EGM 3530-50A TeleFlow, the 3508
TeleTrans Transmitter, the SLC 3740, and the older model RTU 3320. These
devices were suitable for immediate response because each one always had a fixed
set of data inside them, meaning that there could be a fixed set of messages, always
'ready to go'.
Network 3000-series controllers which are 'download-able' do NOT have a fixed set
of data messages, because there is an essentially unlimited set of possible messages,
based on how the user creates their particular ACCOL load. To implement
immediate response in these devices, users must configure an Immediate Response
Delay for the Slave Port. (See Chapter 4.)
An Immediate Response polling transaction can potentially use fewer messages
than BSAP. A successful transaction uses only two messages. If the transaction is
NOT immediately successful, however, immediate response transactions will revert
to the standard six message BSAP transaction.
A successful immediate response transaction is as follows:
1) Data Request: The Master node says to its Slave node "Do you have x for
me?" (Where x refers to a specific type of data, such as a set of certain signal
values, etc.)
(A user configurable delay period then occurs, during which the Slave Node
composes a response containing data x)
2) Response: The Slave node sends a response message to the Master containing
the specific requested data x. The transaction is now considered over.
Note: If the Slave node was unable to obtain the specific requested data x within the
required period, the polling method will revert to standard BSAP, with a DATA
REQUEST, ACK, POLL, RESPONSE, UP-ACK, and DOWN-ACK.
Advantages:
• Message traffic can potentially be reduced by two-thirds.
Disadvantages:
• Not all Network 3000-series nodes support immediate response.
Page B-4 Network 3000 Communications Configuration Guide