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DISC
DISConnect
The DISC statistic is generated when the bridge/router sending the DISC informs the other bridge/router that it (the
sending bridge/router) is suspending its own operation.
Before the DISC is acted upon, the bridge/router receiving the DISC confirms its acceptance of the DISC command
by the transmission of a UA response. The bridge/router sending the DISC enters the disconnected phase when it
receives the acknowledged UA response.
Previously transmitted I frames that are unacknowledged when DISC is generated remain unacknowledged. It is the
responsibility of a higher-level protocol (e.g. TCP, XNS, LAT) to recover from the possible loss of the contents
(packets) of such I frames.
UA
Unnumbered Acknowledgment
A UA response and statistic is generated to acknowledge the receipt and acceptance of the mode-setting commands.
Received mode-setting commands are not acted upon until the UA response is transmitted.
DM
Disconnected Mode
The DM unnumbered response and statistic is generated to report a status where the bridge/router is logically
disconnected from the link, and is in the disconnected phase.
1)
The DM may be sent to indicate that the bridge/router has entered the disconnected phase without having
received a DISC command.
2)
If sent in response to the reception of a mode-setting command, the DM is sent to inform the other
bridge/router(s) that this bridge/router is still in the disconnected phase and cannot execute the Set Mode
command.
A bridge/router in the DM phase will monitor received commands and will react to a SABM command. It will send a
DM response with the F bit set to 1 in response to another command received with the P bit set to 1.
FRMR
FRaMe Reject
The FRMR statistic is generated by the bridge/router to report an error condition not recoverable by the re-
transmission of an identical frame. This may result from at least one of the following conditions:
1)
the receipt of a command or response control field that is undefined or not implemented;
2)
the receipt of an I frame with an information field that exceeds the maximum established length;
3)
the receipt of an invalid N(R); or
4)
the receipt of a frame with an information field that is not permitted or the receipt of a supervisory or
unnumbered frame with incorrect length.
An undefined or not implemented control field is any control field encoding not identified in Table 5, LAPB commands
and responses.
A valid N(R) must be within the range from the lowest send sequence number N(S) of the still unacknowledged frame(s)
to the current logical DCE send state variable, inclusive.
An information field that immediately follows the control field, and consists of 3 to 5 octets, is returned with the FRMR
and provides the reason for the FRMR response.
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