Cisco ONS 15300 Series

ONS15327 Older Revision XTC-28-3 Cards May Exhibit DS3 Bit Errors

Updated April 20, 2005
March 12, 2003

Products Affected


Top Assembly

Part Number






















Problem Description

Some older revisions of the XTC-28-3 and XTC-28-3-T cards may exhibit DS3 circuit bit errors. These earlier version cards do not have optimal frame and signal ground plane layout on the XTC-28 daughter card and could exhibit DS3 bit errors. There are some approved DS1 transformer components on the Cross-Connect, Timing and Control (XTC) daughter card that perform better than other DS1 transformer components.

The determining problem is noise coupling from inactive DS1 circuits (unprovisioned ports) on the XTC daughter card to the DS3s on the XTC daughter card. The signal and frame grounds within the 15327 are DC isolated throughout the system and tied together at a single point on the Mechanical Interface Card (MIC). This results in the potential for a variable voltage difference (noise) between the frame and signal ground planes as other signals pass over them. The inactive DS1 circuits refers to unprovisioned ports (OOS, no circuit).

The issue is most prevalent in systems with STBY XTC-28 cards installed and also prevalent with few or no DS1 circuits provisioned. This is because dual XTC systems are more likely to exhibit the issue because there are twice as many signals passing over the frame and signal ground planes in the system which increase the amount of noise. Systems that are running error free as currently configured are unlikely to begin exhibiting this issue unless there is a change in network topology.

This does not impact the ONS15454 or any other Cisco products.


During ongoing system testing, DS3 circuit bit errors had been observed after the STBY XTC-28 card was inserted into slot 6 and the active XTC card was in slot 5. The test-set showed slow bit error while the node ran for a period of time.

Problem Symptoms

These earlier version cards do not have optimal frame and signal ground plane layout on the XTC-28 daughter card and could exhibit DS3 bit errors. Symptoms include:

  • DS3 circuits may take continuous errors at a low error rate.

  • There will be no PMs reported at the source node for these errors.

DS3 error symptoms have only been observed in systems where at least 50% of the DS1 circuits are not provisioned.


The DS3 daughter card of the XTC-28 card has been redesigned to eliminate the source of the noise coupling.

The following workaround can be implemented if symptoms occur.

Provisioning some, or all, of the DS1 circuits has resolved the DS3 dribbling error problem in all test cases that have been seen. The DS1 ports need to be in service, with circuits provisioned. The DS1 provisioning eliminates the errors on the DS3 circuits.

An upgrade program was offered and was in effect for a period of one year. This program has expired.


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CSCea03040 (registered customers only)

Dribbling DS3 bit errors recorded during steady period

For More Information

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