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FEATURE NEXT-GENERATION PON
As NGPON2 uses different wavelengths from
any previous technology generations it means that TWDM-PON can be deployed on any combination of GPON, XGPON, and NGPON2, all on the same fibre. Conger highlighted the benefits of this flexibility: ‘You could conceivably have eight TDM-PONs on a single fibre and also add in a bunch of overlay wavelengths. So there is a lot of flexibility there, and that was the intent. It borrows a lot of technology from the DWDM technology that is in place for the point-to-point technology today.’ Te NGPON2 standard is still being worked on,
TWDM-PON is backwards compatible, supporting various speeds as well as services
The missing generation Robert Conger, director of global carrier strategy and solutions for Adtran’s carrier networks division, said: ‘If you look across the different PON technologies, GPON is what has been mass-deployed today and it has been around for quite a while now.’ But there were some problems, he continued: ‘Te first FSAN/ITU standard for 10-gigabit PON was XGPON1 which is defined as 2.5 gigabit downstream and 1.25 gigabit upstream – so four times the downstream and two times the
The opportunity window for XGPON1 has closed
upstream bandwidth [of GPON]. Tat standard has basically been in effect since at least 2010, but it was never really deployed in any significant numbers.’ Te reason operators chose not to deploy
XGPON1 in any significant numbers was mainly because the demand for 10 Gb/s bandwidth was not high enough at that time, according to Ana Pesovic, senior marketing manager for the Wireline Division in Alcatel Lucent: ‘I would not say that the opportunity window for XGPON1 is closing, I would say it has closed already,’ she said. ‘We have had XGPON1 since 2010. We have the technology; we did some trials; but we did not see any traction in the market at that time, because it was just too early and people really did not need the bandwidth at that time.’ Other technologies, such as EPON, have had
some success in Asia, but this technology also never found much traction in the US or European markets.
Alcatel-Lucent has future-proofed the ISAM FX by adding support for multiple wavelengths Conger said: ‘10 Gigabit EPON did come to
market and it has been deployed in small numbers over the last couple of years, primarily in markets in Asia. It would have been very comparable to XGPON1, and what would have been XGPON2, but it never came to market. Te teams at FSAN that put together XGPON and GPON standards started working on NGPON2, and most operators are going to wait and jump straight to that.’ NGPON2 products are based on what’s called
TWDM-PON technology, which stands for time- and wavelength-division multiplexing. Conger said: ‘When we talk about GPON and XGPON – all these technologies they are considered TDM [time division multiplexing] PON technologies. Te combination of that with DWDM [dense wavelength division multiplexing] is where you get the name TWDM-PON.’
but the MAC or physical layer that governs, among other things, the wavelengths that will be used is expected to be finalised very soon, explained Conger. ‘Tere is still some work to be done as far as coordinating wavelengths over multiple systems, and then there is the whole control-channel coordination between multiple systems so there are still some further specifications that need to be finished. I wouldn’t say that the standard is 100 per cent complete, but it is definitely complete enough that vendors can begin development.’ One of the main considerations in the new
standard, and indeed any technology that needs to be mass deployed, is of course cost. Tis is one of the main advantages of NGPON2, along with the possibility of the symmetrical 10/10 Gb/s bit rate. Pesovic said: ‘When FSAN was looking at these
options, of course they were looking at the cost; because the point is not to make the best technology that nobody can afford, but to provide a good balance between the cost and the benefits. Tere were actually a lot of technologies that FSAN were looking at, some of them very
Issue 6 • Winter 2015 FIBRE SYSTEMS 27
Alcatel Lucent
Alcatel Lucent
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