[asterisk-users] Suddenly "HDLC Bad FCS (8)" errors on ISDN-PRI, changed nothing

[Gareth Blades]

DLeese at LStelcom.com wrote:
> Hi fellow asterisk users,
> 
> I am running Asterisk 1.4.29 with an Digium TE121 card (wcte12xp kernel
> module) an approx. 100 snom320. The whole installation is running
> without issues since 5 months.
> 
> Without having changed anything on the asterisk server for at least 2
> months, i noticed "clicking sounds" at external calls over the PRI.
> Asterisk constantly throws the following messages:
> 
> ...
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:37] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> [May 31 14:03:38] NOTICE[4163]: chan_dahdi.c:9078 pri_dchannel: PRI got
> event: HDLC Bad FCS (8) on Primary D-channel of span 1
> ...
> 
> At first (last week) there where only a few of these messages per
> minute, but today their intervall inceased dramatically. The "clicking"
> also increased.
> 
> Can this be caused by problems of the telco (Deutsche Telekom)? If so,
> could anybody please provide some additional information about it? Does
> anybody have any experiences with this issue?
> 
> 
> Regards
> 
> Daniel Leese
> 

FCS = Frame Check Sequence and is basically a checksum. You probably 
have crc4 or similar specified on the span line in the configuration 
file. Sometimes there can be an incompatability with the telco which can 
cause this error in which case you can simple disable it.
You might want to try disabling it by removing that parameter from the 
span line but I suspect there is a problem somewhere and removing it 
will remove the error message but you will still hear the clicks.
When I had the problem I removed the option but still got the occasional 
yellow and red alarm which caused all calls to be dropped. It ended up 
being a fault with the card in the telephone exchange.

If you still have issues then try a new ISDN cable and perform a 
loopback test on the card. If that doesnt fix it you will need to report 
a fault with the telco.