[AusNOG] Acceptable dBM loss over SM cross connect in a datacentre

[Thomas Weible - FLEXOPTIX]

>> I have a dark fibre link measured as <4dBm end-to-end over a 13km run,
>>but
>> am seeing 19dBm switch-to-switch in both directions.
>
>19dBm, -19dBm or 19dB?
>
>Loss would typically be measured in dB
>Power would typically be expressed in dBm

This „picture“ might help to understand the diff between dB and dBm (I
hope the ASCII picture is viewable in your client - the spaces are blanks
and no TABs):


                 Transceiver   <-------- Singlemode Fiber  -------->
Transceiver

                 Transmitter (TX)       Attenuation / Loss
Receiver (RX)
Unit:                dBm                       dB                       dBm



>
>Most fibre stuff I've seen seems to transmit from a low end of -10dBm
>(100uW) to +6dBm (4mW).
>
>19dB does seem somewhat excessive to me, but then I'm not an expert in
>this field!
>
>Most receivers I can quickly find specs on seem to indicate they are
>happy 
>working on receive power levels from 0 to -20dBm or so.

You can add these figures to the picture above:


Typical range:    +6 to -9 dBm          0,40dB/km at 1310nm           down
to -23 dBm (10G)
                                        0,25dB/km at 1550nm           down
to -37 dBm (1G)




-> 13km of Singlemode at 1310nm will end up with approx. 5dB attenuation.
Assuming your counterpart transmitter does -7dBm (TX) you will have a
receive level of -12dBm (RX). This should work with a regular LR or LX
transceiver.



Thanks again for the nice meeting
   Thomas