SNAX/HLS Configuration and Control Manual

Treatment of SIG (SIGNAL) Requests
Interpreting SNA Protocol
104705 Tandem Computers Incorporated 7–3
Responses Owed The IBM SNA Format and Protocol Reference Manual: Architecture Logic defines a
procedure named RESPONSES_OWED on page 5-43. This procedure is used to
disallow sending of data in half-duplex modes if the half-session has received but not
yet responded to a request. The procedure, as specified, does not account for the
possibility that the request might have been rejected (that is, a negative response has
been sent), but the correlation-table entry still exists because the end-of-chain or
CANCEL message has not yet been received. During this state, the CHAIN_RCV FSM
is in the PURGE state, but the RESPONSES_OWED procedure still indicates an error.
SNAX/HLS reinterprets this procedure so that a responses owed sense code is
returned using the following algorithm:
If the session is full-duplex, return OK;
If the receive correlation table is empty, return OK;
If there is only one entry in the receive correlation table and the CHAIN_RCV FSM
is in PURGE state, return OK;
Else, return %H200D (responses owed).
Requests Received
When Pacing Window
Is Closed
SNAX/HLS treats the receipt of a request when the receive pacing window is closed
as an error. The sense code generated is %H2011. This value, defined for LU 6.2, is
chosen because it accurately describes the situation.
Size of Received
Messages
SNAX/HLS cannot determine the maximum size of unformatted messages on the
SSCP-LU flow, and, therefore, allows for an upper limit to be configured at startup
and modified during execution. The value must be in the range 256 to 30,720.
However, to avoid needless allocation of memory resources, HLS issues a read of this
size only if the profile attribute specifies that SSCP messages are wanted (WANT-
SSCP-TEXT = Yes).
If SSCP messages are not required, HLS issues reads of at least 256 bytes, and text
overrun errors induced by unformatted SSCP-LU messages are ignored.
Treatment of SIG
(SIGNAL) Requests
SNAX/HLS provides special treatment for received SIG (SIGNAL) requests whose
signal code is %H0001. These requests convey a REQUEST-TO-SEND. As long as
such a request is pending on a session’s input queue, SNAX/HLS discards subsequent
SIG requests with a signal code of %H0001. Furthermore, all SEND-DATA replies
convey the letter Y in the ENTER-RECEIVE-STATE-IND field. These conditions
persist until the data is conveyed to the application by a RECEIVE-DATA response
with a data type of DT-SIGNAL.
Note that SIG requests bearing signal codes other than %H0001 are queued to the
session and are unaffected by the special treatment described above.