Installation guide

2: SLC Protocol Theory of Operation
DC 900-1564A 23
An application can restrict the ICP to block-level retransmissions by setting the maxi-
mum number of message transmission attempts (N3) for the ICP link to 1.
2.2.5 Safe Store Support
Safe store support allows the application to control when each received message is
acknowledged, and to know when each transmitted message has been acknowledged.
For outgoing traffic, the application assigns a message label to each transmitted mes-
sage. The ICP reports receipt of the corresponding acknowledgment.
For incoming traffic, the SLC protocol reports the message label associated with each
message received. The application completes all necessary message protection process-
ing, then sends an acknowledgment to the SLC protocol service on the ICP.
2.2.6 Flow Control Support
Flow control support includes both operator-initiated and automatic flow control.
Operator control can be used per-channel either to command local operational
changes, or to send a flow-control request to the remote site.
For both low-level networks and high-level networks, the SLC protocol defines channel
flow control by means of link control blocks. The SLC software on the ICP conforms to
flow procedures automatically, except when an overriding operator request is in force.
When the ICP receives any link control block that exerts stop/resume flow control, the
ICP sends a
DLI_PROT_CONTROL response to any associated applications with Control
access or Master access. See Table 4–1 on page 33 and Section 5.4 on page 65.
For high-level networks, the SLC protocol also defines network flow control by means
of network control blocks. The application reads or writes an individual network con-
trol block as a special form of the
DLI_PROT_SEND_PRIOR_DATA command or response
(Section 5.13 on page 76).