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[EX] Why does the threshold value show a different value for the same type of SFP optics?

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Article ID: KB22340 KB Last Updated: 14 Dec 2011Version: 1.0
Summary:
This article describes the difference between threshold values of optical power between the same type of SFPs.
Symptoms:
Juniper qualified Optical SFP transceivers support digital diagnostics monitoring (DDM). Customers may need to check the various threshold values, when the power signal warning/alarm is being set. However, The threshold values are shown as different even for the same type of SFP transceivers.


For example, the following output show the difference of the threshold between xe-0/0/0 and xe-0/0/1; even though they are of the same type(SFP -10G-SR):
lab@test> show chassis hardware
Hardware inventory:
Item             Version  Part number  Serial number     Description
Chassis                                DE0211041499      EX4500-40F
Routing Engine 0 REV 17   750-026816   DE0211041499      EX4500-40F
FPC 0            REV 17   750-026816   DE0211041499      EX4500-40F
  CPU                     BUILTIN      BUILTIN           FPC CPU
  PIC 0                   BUILTIN      BUILTIN           40x 1/10GE
    Xcvr 0       REV 01   740-021308   AKF08FM           SFP -10G-SR     Xcvr 1       
REV 01   740-021308   7T511100649       SFP -10G-SR  ...snip....

lab@test> show interfaces diagnostics optics xe-0/0/0
Physical interface: xe-0/0/0
    Laser bias current                        :  7.756 mA
    Laser output power                        :  0.6360 mW / -1.97 dBm
    Module temperature                        :  33 degrees C / 92 degrees F
    Module voltage                            :  3.2830 V
    Receiver signal average optical power     :  0.1056 mW / -9.76 dBm
    Laser bias current high alarm             :  Off
    Laser bias current low alarm              :  Off
    Laser bias current high warning           :  Off
    Laser bias current low warning            :  Off
    Laser output power high alarm             :  Off
    Laser output power low alarm              :  Off
    Laser output power high warning           :  Off
    Laser output power low warning            :  Off
    Module temperature high alarm             :  Off
    Module temperature low alarm              :  Off
    Module temperature high warning           :  Off
    Module temperature low warning            :  Off
    Module voltage high alarm                 :  Off
    Module voltage low alarm                  :  Off
    Module voltage high warning               :  Off
    Module voltage low warning                :  Off
    Laser rx power high alarm                 :  Off
    Laser rx power low alarm                  :  Off
    Laser rx power high warning               :  Off
    Laser rx power low warning                :  Off
    Laser bias current high alarm threshold   :  11.800 mA
    Laser bias current low alarm threshold    :  4.000 mA
    Laser bias current high warning threshold :  10.800 mA
    Laser bias current low warning threshold  :  5.000 mA
    Laser output power high alarm threshold   :  0.8310 mW / -0.80 dBm
    Laser output power low alarm threshold    :  0.2510 mW / -6.00 dBm
    Laser output power high warning threshold :  0.6600 mW / -1.80 dBm
    Laser output power low warning threshold  :  0.3160 mW / -5.00 dBm
    Module temperature high alarm threshold   :  78 degrees C / 172 degrees F
    Module temperature low alarm threshold    :  -13 degrees C / 9 degrees F
    Module temperature high warning threshold :  73 degrees C / 163 degrees F
    Module temperature low warning threshold  :  -8 degrees C / 18 degrees F
    Module voltage high alarm threshold       :  3.700 V
    Module voltage low alarm threshold        :  2.900 V
    Module voltage high warning threshold     :  3.600 V
    Module voltage low warning threshold      :  3.000 V
    Laser rx power high alarm threshold       :  1.0000 mW / 0.00 dBm
    Laser rx power low alarm threshold        :  0.0100 mW / -20.00 dBm
    Laser rx power high warning threshold     :  0.7943 mW / -1.00 dBm
    Laser rx power low warning threshold      :  0.0158 mW / -18.01 dBm

lab@test> show interfaces diagnostics optics xe-0/0/1
Physical interface: xe-0/0/1
    Laser bias current                        :  5.870 mA
    Laser output power                        :  0.5810 mW / -2.36 dBm
    Module temperature                        :  33 degrees C / 91 degrees F
    Module voltage                            :  3.2840 V
    Receiver signal average optical power     :  0.1004 mW / -9.98 dBm
    Laser bias current high alarm             :  Off
    Laser bias current low alarm              :  Off
    Laser bias current high warning           :  Off
    Laser bias current low warning            :  Off
    Laser output power high alarm             :  Off
    Laser output power low alarm              :  Off
    Laser output power high warning           :  Off
    Laser output power low warning            :  Off
    Module temperature high alarm             :  Off
    Module temperature low alarm              :  Off
    Module temperature high warning           :  Off
    Module temperature low warning            :  Off
    Module voltage high alarm                 :  Off
    Module voltage low alarm                  :  Off
    Module voltage high warning               :  Off
    Module voltage low warning                :  Off
    Laser rx power high alarm                 :  Off
    Laser rx power low alarm                  :  Off
    Laser rx power high warning               :  Off
    Laser rx power low warning                :  Off
    Laser bias current high alarm threshold   :  10.500 mA
    Laser bias current low alarm threshold    :  2.000 mA
    Laser bias current high warning threshold :  9.000 mA
    Laser bias current low warning threshold  :  2.500 mA
    Laser output power high alarm threshold   :  1.4120 mW / 1.50 dBm
    Laser output power low alarm threshold    :  0.0740 mW / -11.31 dBm
    Laser output power high warning threshold :  0.7070 mW / -1.51 dBm
    Laser output power low warning threshold  :  0.1860 mW / -7.30 dBm
    Module temperature high alarm threshold   :  75 degrees C / 167 degrees F
    Module temperature low alarm threshold    :  -5 degrees C / 23 degrees F
    Module temperature high warning threshold :  70 degrees C / 158 degrees F
    Module temperature low warning threshold  :  0 degrees C / 32 degrees F
    Module voltage high alarm threshold       :  3.630 V
    Module voltage low alarm threshold        :  2.970 V
    Module voltage high warning threshold     :  3.465 V
    Module voltage low warning threshold      :  3.135 V
    Laser rx power high alarm threshold       :  1.5849 mW / 2.00 dBm
    Laser rx power low alarm threshold        :  0.0407 mW / -13.90 dBm
    Laser rx power high warning threshold     :  0.7943 mW / -1.00 dBm
    Laser rx power low warning threshold      :  0.1023 mW / -9.90 dBm
Cause:

Solution:
Please note, SFP of the same type can be provided by different vendors or suppliers. The supplier's name can be checked from SFP via the Junos chassism. The  commands are:

lab@test> start shell user root
Password:
root@test:RE:0% lcdd 0 chassism
Telnet escape character is '^D'.
Trying 128.0.0.16...
Connected to 128.0.0.16.
Escape character is '^D'.
chassism<0>#show xcvr xe-0/0/0
SFP  Transceiver: SFP -10G-SR
SFP  Transmitter: Enabled
SFP  Vendor Name: FINISAR CORP.
SFP  OUI: 0x009065
SFP  Part Num: FTLX8571D3BCL-J1
SFP  Wave Length: 850 nm
SFP  Serial Num: AKF08FM
SFP  Juniper Info: 740-021308
SFP  Juniper Info: REV 01
...snip...

chassism<0>#show xcvr xe-0/0/1
SFP  Transceiver: SFP -10G-SR
SFP  Transmitter: Enabled
SFP  Vendor Name: SumitomoElectric
SFP  OUI: 0x00005F
SFP  Part Num: SPP5100SR-J3
SFP  Wave Length: 850 nm
SFP  Serial Num: 7T511100649
SFP  Juniper Info: 740-021308
SFP  Juniper Info: REV 0
...snip...


Any Juniper qualified SFP has to meet the Juniper specifications mentioned in the following link:

http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/specifications/optical-interface-ex4200-support.html


For example, the specification of SFP-10G-SR is:

  • Minimum Launch Power

    -7.3 dBm

  • Maximum Launch Power

     -1 dBm

  • Minimum Receiver Sensitivity

    -9.9 dBm

  • Maximum Input Power

    -1 dBm

Even Juniper provides the exact value for maximum and minimum power for the SFPs, the alarm/warning threshold values are programmed by the suppliers themselves.

It could be different from the value in the specification table, as long as they use tighter specification limits than Juniper. For example, the Tx power should be tighter (narrower) than the specification.

In the case of FINISAR, the threshold values of optical output power for warning is:

  • Low Warning

    -5.00 dBm

  • High Warning

    -1.80 dBm

As the minimum Tx power spec is -5.00 dBm and maximum Tx power spec is -1.80 dBm, these values are tighter than the Juniper specification.

On the other hand, the Rx power should be looser(wider) than the specification to receive all of the optical signal. In the case of FINISAR, the threshold values of optical input power for warning is:

  • Low Warning

    -18.01 dBm

  • High Warning

    -1.00 dBm

Their minimum Rx power spec is -18.01 dBm and maximum Rx power spec is -1.00 dBm; these values are looser than the Juniper specification.

Based on the information, the SFP has qualified as it complies with Juniper requirements.



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