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FAQ-EXT_COMM_FAIL Alarm Misreport Generation

Publication Date:  2012-07-25 Views:  89 Downloads:  0
Issue Description


In an overseas office, on a network that runs normally, a site that carries extension subracks reports the EXT_COMM_FAIL alarm that lasts two or three seconds. Sometimes, the NE reports this alarm once in several days. Sometimes, the NE reports this alarm several times a day. Sometimes, the NE reports this alarm several times an hour.
What are the conditions and mechanism of reporting this alarm?
NE software version: 


Alarm Information

Handling Process


If an NE reports the preceding EXT_COMM_FAIL alarm, you can ignore the alarm. Screening the ext_comm_fail alarm does not affect other NEs, because this alarm serves only to check the connection status of the EXT interface. If the cable of the EXT interface is disconnected, the NE reports a bd_status alarm on the related slot.
In the R7 version, this fault is rectified. 

Root Cause
The software code shows that the conditions for reporting the ext_comm_fail alarm are as follows:
When the SSN1AUX board is installed in slot 87, the NE software reads the registers in the BCM5328 chip on the AUX board through the SPI interface to check whether the EXT interface is linked. If the EXT interface is not linked, the software reports the ext_comm_fail alarm without jitter filtering.
Why is the link state incorrect?
The flow of checking the link state of the EXT interface is as follows: The software on the SSN1GSCC SCC reads the registers in the BCM5328 Ethernet switching chip to check the status of the register related to the EXT interface. The software checks the status once every minute. Check error occurs only during the process of reading the register in the BCM5328 chip through the SPI interface.
On the SSN1GSCC, a same SPI interface is connected to the RTC real-time clock, PEB2466, and three BCM5328 chips on the AUX board. The NE software does not perform any operations on the PEB2466, but frequently reads the RTC and BCM5328 chips on the AUX board. The priority of reading the RTC is the highest, that is, 1. The priority of reading BCM5328 registers is set to 100. In this case, when the task of reading the BCM5328 registers is interrupted by the task of reading the RTC, and both tasks are running at a same SPI interface, errors occur in reading the BCM5328 registers. Thus, the ext_comm_fail alarm is generated. The SPI interface conflict occurs in random. Therefore, certain NEs report this alarm once several days, but other NEs report this alarm several times a day.