6100 ADCCP Programming Manual

6100 ADCCP Concepts and Context
Introduction to 6100 ADCCP
069225 Tandem Computers Incorporated 1–15
includes the Nr parameter and can therefore be used to acknowledge received
I-frames.
The command code indicates one of the following types of S-frames:
Receive Ready (RR) Indicates that all frames with sequence numbers less
than Nr have been received error-free and that the
station is ready to accept further transmissions.
A primary station uses this command to poll a
secondary station, or to probe a station that did not
respond to the last command or poll.
Receive Not Ready (RNR) Indicates that the station is busy and that frames with a
sequence number of Nr or greater cannot be accepted at
present. The station may, however, be able to transmit
data.
Reject (REJ) Requests retransmission starting from the frame with
sequence number Nr.
Selective Reject (SREJ) Requests retransmission of the frame with sequence
number Nr.
Unnumbered-Frame Control Field. A U-frame conveys link commands and responses
between a primary station and a secondary station. The control field for this type of
frame is similar to the control field of an S-frame except that the Nr parameter is
replaced by a 3-bit command or response code.
The ADCCP module uses the following commands and responses:
DISC This command is used by a primary station to disconnect a specific
secondary station, or by a combined station to dissolve an ABM link. The
expected response is UA or DM.
DM A secondary station sends this frame when it receives a DISC command or
when an error causes it to become logically disconnected.
FRMR A secondary or combined station sends this response to indicate that it
received an invalid or improperly formatted frame. A frame might be
invalid because it contains a command not implemented at the receiving
station. An example of improper format is a field of a length incompatible
with the configuration.
RD A secondary station uses this response to request a disconnect. The
secondary station goes into the logically disconnected state (LDS) when it
receives a DISC response. RD can be the response to any command.
RIM This response is used by a secondary station to request a SIM command
from the primary station. The secondary can send this response in answer
to any kind of frame to indicate that it cannot respond to other commands
until it has been initialized.
RSET This command is used by a combined station to reset the Nr and Ns
parameters for a pair of substations.