Synchronous Optical NETwork (SONET)

Measuring the Optical Level through IOS

Document ID: 16150

Updated: Sep 19, 2006



This document discusses the options for measuring the optical level of a signal for optical links between Cisco routers. It describes which command to use in order to measure signal level, and provides a reference for determining attenuation and power budget.



There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.


Refer to Cisco Technical Tips Conventions for more information on document conventions.

Measure the Optical Level

Only Gigabit Switch Router (GSR) Engine 4 line cards 1xOC192 and 4xOC48 have built-in power monitoring capabilities. Issue the show controllers optics command in order to view the measured transmit and receive values.

This sample output was captured on the 4xOC48 line card for the GSR.

LC-Slot1#show controllers optics
Rx AC+DC optical power in mWs or dBms
     Port 0 =   0.000 mW
     Port 1 =   0.000 mW
     Port 2 =   0.000 mW
     Port 3 =   0.000 mW
Tx laser diode forward bias current I(F) in milliamps
     Port 0 =   0.000 mA
     Port 1 =   0.000 mA
     Port 2 =   0.000 mA
     Port 3 =   0.000 mA

This sample output was captured on the 1xOC192 line card for the GSR.

LC-Slot4#show controllers optics
Rx AC+DC optical power in mWs or dBms
   AC+DC = -  1.611 dBm
Rx AC optical power in mWs or DBMS
   AC =   0.000 mW
Tx optical power in mWs or DBMS
   power = -  8.239 dBm
TX laser diode forward bias current I(F) in milliamps
   current = 105.830 mA
TX laser diode temperature in degrees centigrade
   temperature =  61.889 C

In addition, the 1xOC-48c/STM-16 POS and 1xOC-48 channelized STS-12c/STM-4, STS-3c/STM-1 or DS3/E3 POS Internet Services Engine (ISE) line cards for the Cisco 12000 Series support power monitoring. Use the show controllers <interface> command in order to view the current levels.

     12404#show diag sum     
     SLOT 1  (RP/LC 1 ): 1 Port ISE Packet Over SONET OC-48c/STM-16 Single 
     Mode/SR SC connector 

12404#show controller pos 1/0     
       LOF = 0          LOS    = 0                            BIP(B1) = 0 
       AIS = 0          RDI    = 0          FEBE = 0          BIP(B2) = 0 
       AIS = 0          RDI    = 0          FEBE = 0          BIP(B3) = 0 
       LOP = 0          NEWPTR = 0          PSE  = 0          NSE     = 0 
     Active Defects: None 
     Active Alarms:  None 
     Alarm reporting enabled for: SF SLOS SLOF B1-TCA B2-TCA PLOP B3-TCA 
     Framing: SONET 
       COAPS = 0          PSBF = 0 
       State: PSBF_state = False 
       ais_shut = FALSE 
       Rx(K1/K2): 00/00  S1S0 = 03, C2 = FF 
       Remote aps status (none); Reflected local aps status (none) 
       RDOOL = 0 
       State: RDOOL_state = False 
       Remote hostname : 
       Remote interface: 
       Remote IP addr  : 
       Remote Rx(K1/K2):   /    Tx(K1/K2):   / 
     BER thresholds:  SF = 10e-3  SD = 10e-6 
     TCA thresholds:  B1 = 10e-6  B2 = 10e-6  B3 = 10e-6 
     Optical Power Monitoring 
         Laser Bias = 2.8 mA 
         Receive Power = -32.04 dBm (+/- 2 dBm)

The benefit of built-in power monitoring is that you can view the actual optical level seen by the card, rather than only the measured value before the fiber is attached to the line card. In rare circumstances, a dirty receive interface can lead to different values on the card than on the wire and in turn to high error rates.

For all other cards, ensure the receiver is clean. Ensure you use the same drop cable with the tester and the card.

Note: Over time, the power of the sender (or last repeater) and receiver sensitivity can fluctuate and fall out of range. In addition, frequently handling the connection can increase the chances of a degraded signal.

Determine the Power Budget

These publications contain information on determining attenuation and Power Budget (PB).

  • T1E1.2/92-020R2 ANSI, the Draft American National Standard for Telecommunications entitled Broadband ISDN Customer

  • Installation Interfaces: Physical Layer Specification

  • Power Margin Analysis, AT&T Technical Note, TN89-004LWP, May 1988

Related Information

Updated: Sep 19, 2006
Document ID: 16150