User`s guide

212 DC 900-1340I
BSC Programmer’s Guide
B.1.3 Signon Procedure using BSC 2780/3780 Software Commands
The BSC 2780/3780 software provides an optional initial signon procedure to allow the
local and remote clients to exchange and validate station IDs after the links are enabled
but before transferring data. Figure B–3 and Figure B–4 illustrate the difference in the
signon sequence due to a change in the timing of the first data block from the client.
In both figures, the initiating (local) client starts by sending a Signon command
(Section 5.4.1.10 on page 126) to the BSC 2780/3780 software with its station ID in the
output buffer of the command. This action causes the sequence LOCAL<ENQ> to be
transmitted on the line. When the remote station responds with REMOTE<ACK0>,
the BSC 2780/3780 software sends a signon response to the client with the remote ID in
the data area of the response. The local client then validates the remote ID and, if the ID
is valid, sends another Signon command to the BSC 2780/3780 software as a confirma-
tion.
In Figure B–3, the client sends the first data block within the allowed two-second time
interval, causing the data to be sent on the communication line rather than EOT. In
Figure B–4, the client delays the first data block beyond the allotted two-second time
period, resulting in an EOT followed by a normal line bid sequence before the data is
sent on the communication line.
Figure B–5 shows a typical signon sequence in receive mode followed by data.
Note
As shown in the figures, each Signon command results in a dlRead
Signon response (the pOptArgs.usProtCommand field is set to
DLI_PROT_SEND_SIGNON by the DLI).