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New Member

ISDN circuit is getting input and CRC errors

We have been beating this one up pretty good and the ISP isn't much help. They have tested and retested the line from the demarc to the local switch several times and have seen no problems, and their records show that the ISDN circuits on the property are no where near the Frame circuits we use.

Here is some background on the configuration and the problem at this property. We have a 1721 router in place at the moment with a Serial interface coming back here to Corp for business applications and a seperate BRI interface that they use for their internet access. They have been having an ongoing problem with the ISDN dropping packets, and getting input and CRC errors. It occasionaly drops the connection and comes back up several times and then just stops. here is a sample of what we are dealing with:

BRI0 is up, line protocol is up (spoofing)

Hardware is PQUICC BRI with U interface

MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

Last input 00:00:02, output never, output hang never

Last clearing of "show interface" counters 20:38:29

Input queue: 0/75/629/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/1/16 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 96 kilobits/sec

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

5661 packets input, 24140 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

629 input errors, 629 CRC, 0 frame, 1 overrun, 0 ignored, 422 abort

7997 packets output, 36499 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

64 carrier transitions

What I need is some help in nailing down this problem. I know the CRCs are caused by something physical. What can I do to troubleshoot this and what are the causes of this type of behaviour?

Keep in mind this is a remote property we manage from Corp, so I do not have physical access to the equipment.

Any help from anyone would be greatly appreciated!


Re: ISDN circuit is getting input and CRC errors

Seems like an issue that I experienced years ago. Then too, it was an ISDN line that was not working due to huge amounts of errors.

The solution was to ground the equipment properly. This might be your issue as well.



New Member

Re: ISDN circuit is getting input and CRC errors

Exactly what equipment needs to be grounded?

Re: ISDN circuit is getting input and CRC errors

The router must be grounded via the mains shield wire. This is normally done via the mains outlet. If this is not available or not good enough, you may connect it to a dedicated ground line.

The ISDN NT1 can be grounded via the telephony cabling or using a dedicated ground.

To test if this is your solution, you may use improvised grounding. In a computer room there is mostly a dedicated gound available but you could also use the central heating or the water pipes for that.



New Member

Re: ISDN circuit is getting input and CRC errors

Could this be caused if the router is plugged into a dirty or faulty power source? I may need to probe the engineer there to see if it is going into the mains or not.

Re: ISDN circuit is getting input and CRC errors

This is definitely a possibility. In my case, the outlet where the router was connected did not have a ground at all.

Through solving that issue (with help from others), I have learned how important grounding is. It's one of those lessons you never forget!


New Member

Re: ISDN circuit is getting input and CRC errors

Good deal... I am going to work on that solution and see where it takes me. I will let you know what my progress is. Thanks!

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