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Intermittent Audio Distortion in AVB Stream with SNTP Client enabled

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TitleIntermittent Audio Distortion in AVB Stream with SNTP Client enabled
Symptoms
  • Audio Distortion on AVB stream
  • gPTP messages not being transmitted by switch port
  • SNTP client enabled on AVB switch
Environment
  • Summit
  • EXOS version 15.3.X and up
  • Audio Video Bridging (AVB)
  • Simple Network Time Protocol (SNTP)
Cause
When SNTP and AVB are enabled on the same switch the gPTP protocol may enter a faulty state causing gPTP enabled ports to operate incorrectly.  This is due to a conflict when both protocols are attempting to access the system clock.  The result of this failure is audio distortion on the AVB endpoints.  
Resolution
Workaround:

SNTP can be disabled on switches participating in AVB networks.  To disable SNTP enter the following command:

disable sntp-client


Resolution:

CR xos0058050 was created to resolve this issue.

Fixed releases:
EXOS 15.6.1
EXOS 15.7.1 patch 1-2
EXOS 15.5.2 patch 1-5


 
Additional notes
This issue can be confirmed by checking the gPTP port counters.  When in the faulty state the transmit counters will not increment.  Example output below:

L3L_K1_U33(65.44).12 #show network-clock gptp ports 2,22 counters 

Port number                                      : 2
gPTP port status                                 : Enabled
------------------------------------------------------------
Parameter                             Receive       Transmit
------------------------------------------------------------
Announce                                 1603              0
Sync                                    13357              0
Follow Up                               13357              0
Peer Delay Request                       1603           1601
Peer Delay Response                      1601           1603
Peer Delay Response Follow Up            1601           1603
gPTP packet discards                        0              -
------------------------------------------------------------

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