Crosstalk Between Ports

For accurate Virtual Cable Test (VCT) cable diagnostics, a maximum Programmable Gain Amplifier (PGA) gain setting and disabled echo canceler are required. This increases sensitivity to crosstalk. Reducing the gain and enabling the echo canceler reduce crosstalk sensitivity. However, this breaks the cable test, leading to invalid Time Domain Reflectometry (TDR) results.

When crosstalk occurs between ports, running the TDR test command on affected ports yields invalid results. This can be detected using the show cable-diagnostics tdr command, as demonstrated below.

device# show cable-diagnostics tdr 1/1/48 

Port      Speed   Local pair  Remote pair Pair status 
--------- -------- ----------------------------------- 
1/1/48    1000M     Pair A                  Invalid 
                    Pair B                  Invalid 
                    Pair C                  Invalid 
                    Pair D                  Invalid 

To minimize crosstalk and ensure consistent and reliable cable diagnostics, it is recommended to manage the activity on nearby ports appropriately. For instance, disabling adjacent ports and halting traffic on ports where line-rate traffic flows produces more accurate results: For more information on line-rate traffic, refer to the RUCKUS FastIron Traffic Management Configuration Guide. For more information on disabling and reenabling specific ports, refer to the RUCKUS FastIron Management Configuration Guide.

device# show cable-diagnostics tdr 1/1/48 

Port   Speed Local pair  Remote pair  Pair status 
--------- -------- ------------ --------------- ------------- 
1/1/48 1000M     Pair A     Pair B     terminated 
                 Pair B     Pair A     terminated 
                 Pair C     Pair D     terminated 
                 Pair D     Pair C     terminated

The pair status "terminated" indicates an active port.