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TomS_
Git-r-done
Premium,MVM
join:2002-07-19
London, UK
kudos:5
reply to 54067323

Re: Fibre / GPON forums

All of the PON implementations I have seen work by sending the same downstream signal to all ONTs, and this is achieved using 1xN way splitters. The ONTs pick out the data that belongs to them, and ignore the rest.

In the upstream direction the ONTs use a TDM based protocol, having time slots in which they can transmit.

If you read some of my earlier posts I linked to datasheets and other information about specific products that achieve this method of operation.

Im not saying that its impossible to have a WDM based PON network, but Ive never seen or heard of one out in the wild. Im sure there are many different ways to achieve the same kind of outcome, we have just been discussing one particular method in this thread.



54067323

join:2012-09-25
Tuscaloosa, AL

said by TomS_:

All of the PON implementations I have seen work by sending the same downstream signal to all ONTs, and this is achieved using 1xN way splitters. The ONTs pick out the data that belongs to them, and ignore the rest.

In the upstream direction the ONTs use a TDM based protocol, having time slots in which they can transmit.

Interesting, that quite different from the PON's I have worked with and yes I can see how it would work.

Let me ask you a question, if an ONT locks up and just sends continuous light how does one go about finding it and how many ONT's can be on a strand before timing gets flakey?


zed173

join:2010-07-17
Mississauga, ON
reply to TomS_

You will have DWDM (or more likely CWDM) in a PON if for example you are doing an RF overlay (ie. like Verizon FIOS or similiar). You could also encounter DWDM from CO -> Remote on a main line before it's peeled off to different feeders to keep your physical fiber usage lower if need be.


lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:1

1 edit
reply to TomS_

said by TomS_:

All of the PON implementations I have seen work by sending the same downstream signal to all ONTs, and this is achieved using 1xN way splitters. The ONTs pick out the data that belongs to them, and ignore the rest.

In the upstream direction the ONTs use a TDM based protocol, having time slots in which they can transmit.

Tom, you are absolutely correct. Both IEEE 802.3ah and ITU-T G.984 GPON standards dictate that method.

If some company wanted to use even simple WDM (let alone "dense" WDM) on top of GPON passive infrastructure, they have to use custom OLT/ONU designs. I am curious to see a link to such a commercial product - if they actually exist.

P.S. ITU uses ATM frames downstream while IEEE uses 802.3 frames. Most OLT/ONUs are "universal" and can support either ITU/IEEE method. However, they can't support WDM without a complete re-design.