SNAX/HLS Configuration and Control Manual

Step 3. Planning Session BINDs
Planning the SNAX/HLS Environment
2–12 104705 Tandem Computers Incorporated
Normal Flow Send/Receive Mode
This attribute determines how the data flow control (DFC) protocol machines behave
in processing user messages. Informally, DFC protocol machines are set to process
inbound and outbound messages either simultaneously (full duplex) or serially (half
duplex). SNAX/HLS supports the following attributes:
FDUX (full duplex). Messages flow in each direction independently.
HDUX-FF (half-duplex flip-flop) without brackets. At session activation, one
session partner is selected as first sender, and the other as first receiver. The
sender posts messages until it voluntarily relinquishes the right to send by setting
the PREPARE-TO-RECEIVE-IND on a SEND verb. A SNAX/HLS application that
is receiving data can detect that it now has the right to send by monitoring the
ENTER-SEND-STATE-IND field.
HDUX-FF (half-duplex flip-flop) with brackets. At session activation, one session
partner is selected as bidder, and the other as first speaker. Using bracket protocol
requires that the session partner be aware of send and receive states. While
between brackets, the session partners are in contention: either can send. The
partner that wins the contention race sends until it sets the CDI.
HDUX-CONT (half-duplex contention). At session activation, one session partner
is selected as contention winner, and the other is selected as contention loser. The
session partners contend for the right to send a message. Initially, both are in the
contention state.
In the BIND message, this attribute is indicated in byte 7, bits 0 and 1. In HLSRDT,
this attribute is specified by the BIND attribute SEND-RECV, where: FDUX
corresponds to 0 in the BIND message, HDUX-CONT corresponds to 1 in the BIND
message and HDUX-FF corresponds to 2 in the BIND message.
Recovery Responsibility
This attribute selects the session partner responsible for session recovery. Set this field
in accordance with device or product capabilities (that is, typically the PLU is
responsible for session recovery if HDUX-FF with brackets is selected as send/receive
mode; otherwise, symmetric recovery is selected).
In the BIND message, this attribute is indicated in byte 7, bit 2. In HLSRDT, this
attribute is specified by the BIND attribute RECOVERY-MODE, where: LOSER
corresponds to 0 in the BIND message and SYMMETRIC corresponds to 1 in the BIND
message.
Contention Winner
This field selects which session partner wins a contention to begin brackets. This field
is used only if HDUX-FF with brackets is used as the send/receive protocol. This field
also identifies which partner will be known as the first speaker (the winner), or the
bidder (the loser).