I have a pair of GLC-LH-SMD devices which are 1000BASE-LX/LH
In the field they will be a couple of kilometers apart , but whilst I test the setup I only have 5m patch leads.
I looked at the specs and Cisco state they are
Transmit Power -3 to -9.5 dBm, Receive power -3 to -20 dBm
So this seems to me to mean that you can connect them with any length cable as the Transmitter maximum is the same as the receiver maximum (-3 dBm)
Yet if I connect them to each with a five meter patch lead to each other (in the same switch) - or if I connect one to itself I get a high RX power warning
Dec 19 22:44:44.946: %SFF8472-5-THRESHOLD_VIOLATION: Gi1/0/1: Rx power high warning; Operating value: -1.4 dBm, Threshold value: -3.0 dBm.t
C3750#sho int g1/0/1 tra
ITU Channel not available (Wavelength not available),
Transceiver is internally calibrated.
If device is externally calibrated, only calibrated values are printed.
++ : high alarm, + : high warning, - : low warning, -- : low alarm.
NA or N/A: not applicable, Tx: transmit, Rx: receive.
mA: milliamperes, dBm: decibels (milliwatts).
Optical Optical
Temperature Voltage Tx Power Rx Power
Port (Celsius) (Volts) (dBm) (dBm)
--------- ----------- ------- -------- --------
Gi1/0/1 27.4 3.30 -5.1 -1.4 +
C3750#sho int g1/0/2 tra
ITU Channel not available (Wavelength not available),
Transceiver is internally calibrated.
If device is externally calibrated, only calibrated values are printed.
++ : high alarm, + : high warning, - : low warning, -- : low alarm.
NA or N/A: not applicable, Tx: transmit, Rx: receive.
mA: milliamperes, dBm: decibels (milliwatts).
Optical Optical
Temperature Voltage Tx Power Rx Power
Port (Celsius) (Volts) (dBm) (dBm)
--------- ----------- ------- -------- --------
Gi1/0/2 33.3 3.30 -5.5 -1.9 +
C3750#
If I connect the transceiver XMT to its own RCV I get
Optical Optical
Temperature Voltage Tx Power Rx Power
Port (Celsius) (Volts) (dBm) (dBm)
--------- ----------- ------- -------- --------
Gi1/0/1 31.4 3.30 -5.5 -1.9 +
I don't see how a transmit power of -5.5 dBm is being received as -1.4 dBm so my question is , Is it real - how am I receiving more power than I transmit? Can I control the transmit power ? (other than inserting the lead but not clicking it into place - which actually seems to work as shown by the receive level below
Optical Optical
Temperature Voltage Tx Power Rx Power
Port (Celsius) (Volts) (dBm) (dBm)
--------- ----------- ------- -------- --------
Gi1/0/1 31.8 3.30 -5.1 -13.0
And more importantly is this a problem ? I can see that the 1000BASE-ZX has a much higher transmit power than a receive power - so this would need an attenuation cable