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New Member

Serial T1 Increments RUNTS and ABORTS on one end only.

Runts indicate discarded packets because they are smaller than the mediums minimum packet size.

What is a the minimum packet size for a full T1?

The runts are probably causing the aborts, right? Or vise-versa.

Cisco trouble-shooting documentation tells me:

Aborts usually indicate a CLOCKING problem between the serial interface and the data link equipment. I have Internal CSU/DSU on 7206s' at both ends of this link. One ends clocking is set to INTERNAL, the other is set to LINE.

No other errors are showing - no framing, interface resets, drops, etc.

This works properly on all my other WAN links.

Thanks in advance.


Re: Serial T1 Increments RUNTS and ABORTS on one end only.

Work with your service provider have them test from varios test point i.e. closest DAX far end DAX , ddetermine what they can and can not loop and run a good test pattern to , i.e smart jack CSU . This will help determine where the problem lies, bad 4 wire cable bad v.35 bad card internal csu misconfigured .

Re: Serial T1 Increments RUNTS and ABORTS on one end only.

Try extended pings - allows you to enter the 2-byte data pattern, in hexadecimal format, that is repeated in the payload of the ping packet. Three useful ping data patterns that expose line problems include the following:

0x0000 - Line-code mismatches

0xFFFF - Repeater power problems

0x4040 - Timing problems

The 0x4040 extended ping pattern also enables you to detect jitter and

wander. T1 phase variations greater than or equal to 10Hz are considered

jitter, and variations less than 10Hz are considered wander.

Try setting both ends to clock source line (usually the line is the source). If that doesn't fix it, get your provider to perform tests on the line. You can also do loopback testing of your own.

Hope it helps.


New Member

Re: Serial T1 Increments RUNTS and ABORTS on one end only.

Do a show controller t1 x/x and see if you are taking any errors there. If you are taking slips then you most likely have a clocking problem. Your T1 might be run through some teleco equipment that is providing the clock, in which case going to line timing on both sides may help. The inverse of the that may be the telco equipment is set to recieve timing, in which case internal-internal would be needed. Internal-Internal timing i don't see to much of, but line-line is a possiblity.

Last but not least, an external loopback plug will help you test your equipment better than software loopback commands.

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