SNAX/HLS Configuration and Control Manual

7 Interpreting SNA Protocol
104705 Tandem Computers Incorporated 7–1
This section contains miscellaneous notes on how SNAX/HLS uses the SNA protocol.
The presentation presumes a fairly detailed knowledge of SNA. For more information
on this subject, consult the SNA references listed in “About This Manual.”
Response Protocols
SNAX/HLS uses the BIND image to determine which response protocol to use. This
determination is modified by the application program's use of the NOTIFY-IND
modifier on the SEND-DATA and SEND-AND-RECEIVE-DATA verbs. The following
table shows the protocol actually used:
Table 7-1. Selection of Response Protocols
Response Protocol Specified in BIND Response Protocol Actually Used
NOTIFY -IND = N NOTIFY-IND=Y
None No response Illegal
Exception Exception Illegal
Definite Definite Definite
Definite or exception Usually exception Definite
The two cases marked as illegal are forbidden by the verb interface; you cannot ask for
notification if SNAX/HLS is prevented from demanding a response.
The case marked as Usually Exception is a case where SNAX/HLS attempts to
optimize the flows. Except under the conditions listed below, SNAX/HLS will use
Exception Response Chains. The only condition under which SNAX/HLS will select
Definite Response Chains is if all the following conditions hold:
The session is using brackets.
The session is between brackets.
You are using FM-PROFILE 2 (which does not support the BID message).
Under these specific conditions, the only way to bid for the bracket is by including the
BBI (Begin Bracket Indicator) on the first element of the chain. This requires the use of
Definite Response chains.
Bracket Initiation The application program does not directly bid for brackets. Instead, SNAX/HLS
performs the bid on its behalf. When SNAX/HLS tries to send data and discovers that
brackets should be initiated and that the application half-session is the bracket bidder
(rather than first speaker), SNAX/HLS does one of the following:
If the data does not exceed one RU and definite responses are used, it is sent
directly with the BB indicator set.
If the data exceeds one RU or definite responses cannot be used, an SNA “BID”
message is used.