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Metro 100 reports bit errors due to the line fiber type is G.655

Publication Date:  2012-07-24 Views:  109 Downloads:  0

Issue Description

A newly deployed Metro 100 reports lots of "RSBBE", "MSBBE" and "HPBBE". As the consequence, the PD1 board reports "TU_AIS" frequently and traffic is not available. 

Alarm Information


Handling Process

1.Measure the input power of Metro 100 with optical power meter, and the input power is -18dBm, which is a normal input power;
2.Check the original SFP module on Metro 100. It was 1310nm (15km) type. Then replace it by a 80km 1310nm SFP to chase a longer trasimission distance. However, the Metro 100 reports "R_LOS" after this;
3.The actual power is -18dBm wile Metro 100 can not detect it when using 1310nm SFP, it appears that the line fiber type is mismatched with the SFP module type;
4.Query the fiber type with customer, and customer confirmed there are some spans use G.655 fiber on this link;
5.1310nm signal can not be transmitted by G.655 fiber. Because the cut-off wavelength of G.655 is 1480nm, so 1310nm signal will be degraded heavily on G.655 fiber due to wrong dispersion;
6.Replace the SFP module to 1550nm type. Now the bit errors are gone. 

Root Cause

 When SDH equipments report B1 bit error, normally there are two possibilities:
1.The input power of SDH is not normal;
2.The fiber type is mismatched with SFP module type . 


1.1310nm signal can not be transmitted by G.655 fiber due to the cut-off wavelength of G.655 is 1480nm;
2.When bit errors occur and input power is normal, most likely it’s due to SFP module is not compatible with fiber type.