Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

DS3 interface flaps between 7206 VXR WITH PAT3+ and 3745 NM1 WITH T3-E3

I am from the carrier side of the networking house, providing an international DS3 link between my customers router interfaces.

The equipment is as follows:

Site 1: Cisco 7206 VXR WITH PAT3+ ADAPTER


My customer has observed flapping on their DS3 interaces. I am unable to correlate this condition with anything on the DS3 line itself. ANY problem with the DS3 (errors, dropouts, etc) would be observable from the various monitors I have in place. I can't help but suspect the equipment, even though I have been able to test successfully, for days at a time through to payload loops in the DS3 interfaces separately. Is there anyone who may know of a compatibility issue between these two adapters or routers?

From my customers router logs I can see that the flap is originated from the interface at site 2. The customer has an SNTP server so the time stamps in the logs are accurate. The condition is observed over a 30 second period resulting in about 18 carrier transitions and a total time for the interfaces being down of about 10 seconds. Another interesting thing I've noted from their logs is that the interfaces seem to go down for a perfect second before coming up (to the thousandth of a second).

Any insight would be greatly appreciated.




Re: DS3 interface flaps between 7206 VXR WITH PAT3+ and 3745 NM1

There is a sensitivity problem with some of the line interface unit (LIU) used on the PA-A3-T3 port adapter might cause the interface to flap with or without any line error condition reported .This can be solved by installing a 75 ohm fixed attenuators on the Rx side of the port adapter.

New Member

DS3 interface flaps between 7206 VXR WITH PAT3+ and 3745 NM1 WIT

This could also be an issue with the transmit of a particular data stream to the downstream nodes in the telco network.  If they see a data pattern that simulates an error condition, they could alarm and cause carrier transitions.  The solution in this case where 75 ohm cables are installed and db levels have been checked at both ends, could be to enable scrambling on the interfaces.  Scrambling prevents the transmission of the data pattern that causes the telco equipment to alarm, hence resolving the issues.