In one paper I have seen one architecture as given in attached file. for downstream transmission suppose 4 wavelengths are transmitting each at 10 GBPS. So total effective data rate is 40 GBPS. At remote node there is one 1X4 power splitter to provide service to 4 ONUs. Each output port of splitter will consists all four wavelength each at 2.5 GBPS (If I am right). Now Each ONU can receive (or tuned at single wavelength at a time) only one wavelength and that wavelength will only provide 2.5 GBPS.
Now I want to know that what is the need of 4 transmitters or Hybrid TWDM PON at OLT when in TDM PON, only one transmitter will be able to provide 2.5GBPS to all four ONUs ??
Dear Amit,
where is the attached paper? Can you give me the reference? Thanks.
I'll try to answer your question. It seems that your confusion comes from the fact that both in TDM-PON and TWDM-PON, the data rate each ONU can get is the same:2.5Gb/s, is that right? In fact, for TDM-PON, the data is multiplexxed in time domain, which means that if a time slot is occupied by one ONU, then this time solt can not be used for other ONUs (we do not expect the same data for all users, because it's the Internet, not a radio or a TV).In this way, the bandwidth for each user in TDM-PON would be 2.5/N(N refers to the ONU numbers). But if more wavelengths are used, the ONU can use the same time slot on another wavelength, thereby increasing the bandwidth of each user. Hope that I have make my point clear.
Correct Sir, I am little bit confused about TDM and TWDM. Still I am more confused how bandwidth is divided in TDM PON [as I know in TDM PON power is divided while whole data (all wavelengths) is transmitted to all ONUs].
Now my one more doubt by reading your comment is that how in TWDM PON, each ONU can access more then one wavelengths at the same time slot as it can be tuned on at particular wavelength at a time.
In TWDM-PON, each ONU can only get access to one wavelength from 4 by using a tunable filter. Try to think in this way, in TDM-PON, 32 users share the 2.5Gb/s data rate on a single wavelength, while in TWDM-PON, we have 4 wavelengths, then one wavelength is only used by 8 users, that's how the capacity upgrades. (Just an example for easy understanding, in real application, the bandwidth allocation should be determined by the DBA according to the data traffic condition )
Thanks a lot sir for clearing my doubt and helping me to understand my problem. Now please also explain me how the bandwidth for each user in TDM-PON is divided to 2.5/N(N refers to the ONU numbers)??
TDM means time division multiplexing, where the capacity is divided into a lot of small cells in (time slot))in time domain. Each user send its request to the OLT, and the OLT will determine which time slot is assigned to which ONU. With the help of agreements, each ONU can only decode the data on its own time slots and throw away the data on other time slots that do not belong to it.
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