Cabletron Systems FRM User Manual - page 136
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Frame Relay Module 4. 0 User G uide, Rev 01
node will send an XID command to the remote node to indicate that the SDLC device
should be polled for an XID.)
T1
is the Reply Timer, which is used to detect the failure to receive a required acknowl-
edgment or response from the remote link station. The link station will start the timer
when it transmits one of these:
●
an Information LPDU (LLC protocol data unit).
●
a Command LPDU with the P bit set to
B'1.'
(If this LPDU is sent while the timer
is already running, the link station will reset and restart it.)
The link station will reset
T1
when it receives one of these:
●
A REJ (Reject) LPDU, provided a Command LPDU with P bit set to
B'1'
is not
outstanding.
●
A Response LPDU with the F bit set to
B '1.'
●
An Information or Supervisory LPDU with an N
R
greater than the last N
R
received and less than or equal to the line station's V
S
, provided a Command
LPDU with P bit set to
B'1'
is not outstanding.
If additional LPDUs are set from the remote link station after the local station has reset
T1
, the timer will be restarted if acknowledgments of or responses to those LPDUs are
outstanding. If no acknowledgments/responses are outstanding, the link station will
start the inactivity timer. (See "
Ti
" later.)
If
T1
expires and acknowledgments/responses are still outstanding, the link station
will send one of the following, then restart
T1
:
●
A Supervisory LPDU with the P bit set to B'1,' to solicit remote link station
status.
●
Any Unnumbered LPDUs that were not responded to the first time they were
sent.
If acknowledgments/responses are still outstanding after
N2
tries (see that entry), the
link station will declare the link inoperative.
The value specified for
T1
should allow for any delays introduced by the MAC sub-
layer (e.g., queuing).
T2
is the Receiver Acknowledgment Timer, used by the link station to delay sending an
acknowledgment of a received Information LPDU. The timer is started when the
LPDU is received and reset when the acknowledgment is sent. If the timer expires
before the acknowledgment is sent, it must be sent as soon as possible.
Ti
is the Inactivity Timer, used by the link station to detect an inoperative condition in
either the remote link station or the transmission medium. The timer will be started if
T1
has been reset (for one of the reasons listed under "
T1
" earlier), and additional
LPDUs have been sent by the remote link station, and there are no outstanding
acknowledgments or responses from the local link station.
If the local station does not receive an LPDU before
Ti
expires, the station must send
an LPDU with the P bit set to
B' 1'
to solicit the remote station's status. Recovery then
proceeds as described under "
T1
" earlier.