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Community Member

15540ESPx - What will the "Thru" really pass ?

Has anyone out there implemented a MTP pass through solution ?

I have a 3 node optical ring ( 1, 2, 3) . There are a total of 8 channels ( A1-4), (B1-4) that will go through these nodes.

However on node 2 - the middle node I need to drop channels A1, A2, A3.

Channels A4, B1, B2, B3 need to be proceed to node 3 directly.

I am looking at the option of " MTP pass through" . The distance is short enough that I do not have to regen.

However, here is what I need to be clear on . Will the pass through really carry my A4 channel along with the B band ?

I am assuming there will be no transponder /demuxing of A4 on the client side, but is that assumption sufficient ?

Also if "cross connect cable drawer" is my only option are there any links that one could refer me to to get a better understanding of its implementation ?

Thank you,


Community Member

Re: 15540ESPx - What will the "Thru" really pass ?


To drop the 3 channels at Node 2 coming from Node-1 you will need a Band A OADM (let's say East). This will drop all 4 channels in the band at this node, and pass any other channels/bands (ie Band B) out the thru port. You would then have a Band A OADM in the West side, providing the trunk to Node-3. By patching the thru in/out ports of these East/West OADM's together, you pass the Band B channels through Node-2 without regen.

To be able to take Channel 4 from Band A and selectively reinsert it back into the trunk to Node 3 without regen/termination, you will need to use the cross-connect drawer. The demuxed channels in Band-A are presented as an MTP connection on the OADM. These would be patched to the cross-connect drawer using an MTP to 8MU patch cable (provided as part of a cable kit). The 8 MU connections correspond to 4 x Tx/Rx for each channel. You would then use another 2 x MTP to 8MU patch cables, using one to connect to the West-bound OADM MTP connection and the other to connect to the linecard motherboard which houses the transponder to be terminated at Node-2 (Ch 1,2,3). Using MU-MU jumpers you then patch Ch 4 through to the OADM, and Ch 1,2,3 to the LCMB.

At Node-3, you will receive the Band B channels PLUS Channel A4, although A4 will have lower power as it has been through a full demux/mux at Node-2 while B1-4 where optically passed-through.

In the reverse direction the same applies, but you will need to check the optical budget calculations in both directions.

For more info on the Cross-connect drawer, try the test and Turnup Guide:

Hope this helps.



Community Member

Re: 15540ESPx - What will the "Thru" really pass ?

Rob - That was a great explanation. I have been able to draw these out on paper. I am still a little confused about how the A4 channel on the East-bound OADM will connect from the LineCard side on the cross connect drawer to the MTP on the West-bound OADM.

The reason, I need to drop A1, A2, A3 on the West-bound side too. So I must use the cross-connect drawer there too, right ? If so, its MTP connection is already used to go to the cross-connect drawer. So where should my MU-MU jumper from Ch-4 on East bound drawer go to ?

I hate to bother you with these nitty gritty details but you clearly are quite knowledgeable and by far the only one that could explain the details, hence the question.

Another more important thing is the power divergence on Ch-4. Is there any way I can simulate the Ch-4 pass through just to get an idea of kind of losses

we will be looking at. I do not have the cross connect drawer and all the necessary cables yet.

Currently our signal budget from Node-1 to Node-3 with a jumper at Node-2 looks as follows:

Node 1:

wave 2/2

Receiver power level: -14.57 dBm

wave 2/3

Receiver power level: -15.39 dBm

Node 3:

wave 2/2

Receiver power level : -14.21 dBm

wave 2/3

Receiver power level : -14.78 dBm

Thank you once again for an insightful explanation.

Community Member

Re: 15540ESPx - What will the "Thru" really pass ?


I was assuming that ch A1,A2,A3 only went between Node 1 and Node 2 and only A4 went all the way to Node 3. If this right? or do A1,A2,A3 also run Node 2 to Node 3?

If my assumption was right, then I'll try to illustrate what I had in mind:

Basically you will need 3 MTP-8MU cables running into the cross-connect drawer. 1 x OADM (E), 1 x OADM (W) and 1 x LCMB.

You need to patch Ch A1,A2,A3 from OADM (E) to LCMB and Ch A4 from OADM (E) to OADM (W).

eg (hope this works out)




......\ __\__\______/...../..../



If you also run A1,A2,A3 from Node 2 to Node 3, you would add another MTP-8MU cable from the second LCMB to the CC drawer and would would patch A1,A2,A3 from LCMB 2 into OADM (W) in the ports which are unused above.

You could simulate the losses applied by Node 2 but as Band A and Band B would be affected differently, you would need two simulations.

For the actual values, refer to Table 4-7 of the Planning and Design Guide - Optical Budgets:

Simulation 1 - Band B passthru loss - applies to Band B end-end

Attenuate by 2 x 4ch+1 passthru loss

Simulation 2 - Ch A4 cross connect loss - applies to Ch A4 end-end

Attenuate by 2 x 4ch+1 mux/demux loss + cross-connect drawer loss.

Note that the loss values shown are worst-case and real-life values should be lower.



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