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Switching Between SSCP-LU and LU-LU Sessions
The 3708 allows its end users to switch between their LV-LV session and the
supporting SSCP-LV session. Direct communication with the SSCP is possible in
both LV type 1 NTO and LV type 2 operations.
SSCP Communications before the BIND
Before a BIND is received and after the ACTLV, all data input to the 3708 is
transmitted to the SSCP. Typically, this action occurs during an application logon.
All data is translated using the standard 3708 default translate table and no data
formatting or manipulation is performed by the 3708.
SSCP data directed to the terminal is translated by the 3708 using its default
translate table and no formatting is performed by the 3708. NL characters received
from the host, however, is converted by the 3708 to a CR LF.
SSCP Communications after an LU type 2 BIND
After receiving an LV type 2 BIND, the 3708 establishes the LV-LV session. The
3708 indicates the successful establishment of an LV-LU session by displaying
4BMYJOB
on the 3708's status line. The notation
MYJOB
indicates that the user is in an
LV-LU session.
The terminal operator may switch from the LU-LU session to the supporting
SSCP-LV session by pressing the SYS REQ key sequence. Pressing the SYS REQ
key sequence clears the terminal's screen and
MYJOB
is replaced by
SSCP
on the
terminal's status line.
Pressing the SYS REQ key sequence interrupts communication taking place during
the LV-LV session without waiting for completion of outbound chains. As long as
the LV-LV session remains bound, depressing the SYS REQ key sequence again
switches back to the LU-LV session.
The terminal may only be in communication with the host PLU or the SSCP.
Communication to both the SSCP and the PLU is not supported. Any attempts to
send FM data by the SSCP/PLU not currently in communication with the terminal
is rejected by the 3708.
Data messages from the SSCP consists of byte strings containing SCS control codes
and SSCP-supported graphic codes. The only valid SCS control codes are NL,
NULL, IFS, and IRS. NULL, IFS, and IRS are treated as graphic characters and
are displayed as a blank, an asterisk, and a semicolon, respectively. Any other
binary combination in the SCS data stream is treated as a graphic. The characters
appearing on the screen for code points other than supported graphics cannot be
predicted.
Each message from the SSCP is displayed at the current cursor address. When the
3708 receives an NL control code in the SSCP message, it inserts nulls in the
character positions remaining in the display line being written and position the
cursor at the leftmost position of the next line. Characters following the NL code
are displayed beginning at the new cursor position. The message wraps to the top of
the screen if the last line on the screen is written and additional characters remain in
the message.
Chapter 3. SDLC and SNA Communication
3-49
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