Envoy ACP/XF Application Programming Manual

Features Common to Bit-Synchronous Protocols
EnvoyACP/XF Application Programming Manual–132179
B-13
Unnumbered Information-Transfer (UI) Responses
Your application issues a CONTROL 14 procedure call to direct EnvoyACP/XF to
transmit a RIM frame.
Unnumbered Information-Transfer (UI) Responses
The UI response transfers an information field to a primary/combined station without
affecting the number sent (Ns) and number received (Nr) variables. An information field
may be present.
Your application directs EnvoyACP/XF to transmit a UI command by using a WRITE or
WRITEREAD procedure call to place the value in the first byte of the MCW.
Recovery Response (FRMR)
U-frames provide only one recovery response, FRMR.
EnvoyACP/XF transmits the FRMR (frame reject) response to report an error condition
that retransmitting the identical frame will not rectify. These error conditions include:
•
Receipt of an invalid control field.
•
Receipt of an I-frame or U-frame with an information field that was too long.
•
Receipt on an invalid Nr from the remote primary/combined station.
An information field, which provides the reason for the frame reject response, follows
the FRMR.
Your application does not transmit FRMR; EnvoyACP/XF transmits FRMR
automatically.
Other U-Frame Responses
The U-frame responses XID and RD also are available.
XID
A secondary/combined station transmits an XID response to reply to an XID command.
The XID response may or may not include an information field containing the
identification of the transmitting secondary/combined station.
Your application directs EnvoyACP/XF to transmit a XID command by using a WRITE
or WRITEREAD procedure call to place the value in the first byte of the MCW. See the
WRITE, WRITEREAD, and READ procedures in Section 4, System Procedure Call
Specifics for EnvoyACP/XF.
RD
A secondary station transmits the request disconnect (RD) response to request a DISC
command from the primary station.