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List:       linux-atm
Subject:    signaling failures
From:       Mike Westall <westall () cs ! clemson ! edu>
Date:       2000-10-31 22:10:21
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It appears that under very heavy loads my old IBM 8285 switch is
initiating SSCOP disconnects for unknown reasons. (This is version 0.78
of the protocol augmented by me to timestamp signaling log messages).

In the following log extract you will see poll/stat exchanges
at roughly 15 second intvls (889, 903, 918).. but then in the
918 second the switch begins to poll very rapidly and disconnects
after 4 iterations.  The lines starting with * are send/receive
events on vci 5 as logged by the device driver. The killall -USR2
dump provides no additional information.

This nasty situation seems always to be triggered by dropping
of what is presumably a signaling packet. Exactly one packet
is being dropped (as reported by internal driver counters).
The send events are logged at the the point DMA of the packet
to the board is initiated and so I have no reason to believe
the responses are being lost. The board is NOT hung in any way.
Occasionally, the stack recovers on its own when SAAL restarts,
but usually it is necessary to stop and restart the stack (since
the switch ends up in a state in which all new connection attempts
are immediately RELEASED). After the stack is stopped and
restarted, everything works normally again (without the need
to reload the driver.)

Any insights into the following questions would be greatly
appreciated..

(1) Are there situations in the signaling protocol for
    which the loss of a single PDU is SUPPOSED to require
    a SAAL restart for recovery??

(2) If not, is there anything "obvious" in the exchange
    that explains what motivated the switch to send the
    END PDU?


Mike


 973023889:049134 atmsigd:IO: ----------
 973023889:049166 atmsigd:IO: FROM NET (0.0.5): POLL PDU (8 bytes)
 973023889:049206 atmsigd:IO:  00 00 00 22 0a 00 00 16
 973023889:049229 atmsigd:IO: TO NET (0.0.5): STAT PDU (12 bytes)
 973023889:049291 atmsigd:IO:  00 00 00 22 00 00 00 34 0b 00 00 16
 973023889:049134 atmsigd:IO: ----------
 973023903:920073 atmsigd:IO: TO NET (0.0.5): POLL PDU (8 bytes)
 973023903:920121 atmsigd:IO:  00 00 00 23 0a 00 00 11
*973023903.920000 snd (48, 8) vci 5
 973023903:923989 atmsigd:IO: ----------
*973023903.920000 rcv (48, 12) on vci 5
 973023903:924027 atmsigd:IO: FROM NET (0.0.5): STAT PDU (12 bytes)
 973023903:924079 atmsigd:IO:  00 00 00 23 00 00 00 1b 0b 00 00 11
*973023918.260000 RFred exception at  State is 8515 Status is 208
*973023918.260000 rcv (48, 8) on vci 5
 (Repeated 12 times)
 973023918:276770 atmsigd:IO: ----------
 973023918:276983 atmsigd:IO: FROM NET (0.0.5): POLL PDU (8 bytes)
 973023918:277027 atmsigd:IO:  00 00 00 23 0a 00 00 16
 973023918:277063 atmsigd:IO: TO NET (0.0.5): STAT PDU (12 bytes)
 973023918:277211 atmsigd:IO:  00 00 00 23 00 00 00 34 0b 00 00 16
*973023918.270000 snd (48, 12) vci 5
 973023918:279604 atmsigd:IO: ----------
 973023918:279636 atmsigd:IO: FROM NET (0.0.5): POLL PDU (8 bytes)
 973023918:279770 atmsigd:IO:  00 00 00 24 0a 00 00 16
 973023918:279797 atmsigd:IO: TO NET (0.0.5): STAT PDU (12 bytes)
 973023918:279844 atmsigd:IO:  00 00 00 24 00 00 00 34 0b 00 00 16
*973023918.270000 snd (48, 12) vci 5
 973023918:280165 atmsigd:IO: ----------
 973023918:280194 atmsigd:IO: FROM NET (0.0.5): POLL PDU (8 bytes)
 973023918:280324 atmsigd:IO:  00 00 00 25 0a 00 00 16
 973023918:280356 atmsigd:IO: TO NET (0.0.5): STAT PDU (12 bytes)
 973023918:280403 atmsigd:IO:  00 00 00 25 00 00 00 34 0b 00 00 16
*973023918.280000 snd (48, 12) vci 5
 973023918:282882 atmsigd:IO: ----------
 973023918:282920 atmsigd:IO: FROM NET (0.0.5): POLL PDU (8 bytes)
 973023918:282962 atmsigd:IO:  00 00 00 26 0a 00 00 16
 973023918:282987 atmsigd:IO: TO NET (0.0.5): STAT PDU (12 bytes)
 973023918:283033 atmsigd:IO:  00 00 00 26 00 00 00 34 0b 00 00 16
*973023918.280000 snd (48, 12) vci 5
 973023918:283305 atmsigd:IO: ----------
 973023918:283335 atmsigd:IO: FROM NET (0.0.5): END PDU (8 bytes)
 973023918:283461 atmsigd:IO:  00 00 00 00 13 00 00 00
 973023918:283498 atmsigd:IO: TO NET (0.0.5): ENDAK PDU (8 bytes)
 973023918:283548 atmsigd:IO:  00 00 00 00 04 00 00 00
*973023918.280000 snd (48, 8) vci 5
 973023918:285977 atmsigd:SSCF: entering state 1/2
 973023918:286021 atmsigd:SSCF: entering state 2/2

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