9-12 Smart Switch 1800 4. 0 User Guide , Rev 0 1
IDBLKis used in conjunction with IDNU M in generating the Node field in an XID frame
(format 0 or 3) to e stablish a link station co nnection to the host. A f urther explanation
is provi ded un der "ID NUM."
IDNUMis used in conjuction with IDBLK in g ener a ti ng the N o de fie ld i n an XID fram e (fo rm at
0 or 3) to estab lish a link station connection to the host. If both IDBL K an d IDNU M are
set to 0, the Node field of the XID will be prov ided by the attach ed SDLC d evice. (The
node will send an XID command to the remote node to indicate that the SDLC dev ice
shoul d be polle d for an X ID.)
T1 is the Reply Timer, used to detect the f ailure to receiv e a required acknowled gment o r
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 wh ile 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 In form a tio n or Sup erv i sory LPDU w ith an NR greater than the last NR
received and less than or equal to the line station's VS, provided a Command
LPDU with P bit set to B'1' is not outstanding.
If additional LPDUs are set from the remote link s tation after the local station has reset
T1, the timer will be restarted if acknowledgments of o r responses to those LPDUs are
outstanding. If no acknowledgments/responses are outstanding, the link station will
start the inactivity timer. (See "Ti.")
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 acknowledged when first sent.
If acknowledgments/responses are still outstanding after N2 tr ie s (see that entr y), 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., qu euin g) .
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 ack no wledg ment i s sent, i t must be sent as s o on as po ssib l e.