Part 2: Next-generation passive optical networks
The Full Service Access Network (FSAN) has outlined its vision for fibre access networks for the coming decade.
FSAN is an industry forum that includes over 20 operators and 70 members overall. The group identifies service requirements and develops optical access technologies that are passed to the International Telecommunication Union (ITU) for standardisation.
“One of the messages of the roadmap is that, in the immediate future, what FSAN wants to do is evolve the existing standards,” says Peter Dawes, FSAN NGPON co-chair.
The latest FSAN technologies to become standards are XGS-PON (10 gigabits symmetrical passive optical network) and the multiple wavelength TWDM-PON (time wavelength-division multiplexing passive optical network), also known as NG-PON2 (see chart).
XGS-PON is a single-wavelength PON standard that supports two rates: a 10-gigabit symmetrical rate and the asymmetrical 10 gigabits downstream (to the user) and 2.5 gigabits upstream originally introduced by XG-PON.
TWDM-PON uses four wavelengths to deliver up to 40 gigabits of symmetrical bandwidth and has an option for eight wavelengths overall. TWDM-PON also uses tuneable lasers enabling operators to move subscribers between wavelengths.
“FSAN operators see continued growth in PON deployment,” says Dawes. “There is still strong deployment of GPON and we are on the verge of needing 10-gigabit symmetrical services.” Other operators may delay and go straight to TWDM-PON, he says.
According to Dawes, operators are seeing a variety of applications that are driving the need for 10-gigabit access rates. One is the growing use of video and video conferencing. Another bandwidth driver for access networks is mobile applications such as connecting mobile antennas and mobile backhaul. In addition, there are digital home trends such as social networking and the moving of content to the cloud.
Mobile fronthaul can eat as much bandwidth as you can supply once you start to aggregate [radio] antennas
Operators are also keen to attach the labels ‘gigabit’ and ‘gigabit services’ to their broadband offerings as a marketing differentiator.
Other drivers for the move to the newer PON technologies include peer-to-peer services and business IP services, says Dawes.
FSAN’s plan to evolve the existing standards in the near term will take the group to 2021.
One obvious way the existing PONs can be evolved is to adopt 25-gigabit wavelengths. This would enable a 25-gigabit symmetrical extension to XGS-PON and a future TWDM-PON variant with up to 200 gigabits of capacity if the full eight wavelengths are used. “It is a case of looking for logical evolutions of these technologies,” says Dawes.
One application that could use such high capacities is mobile fronthaul, says Dawes: “It can eat as much bandwidth as you can supply once you start to aggregate [radio] antennas.”
After 2020, FSAN will investigate disruptive technologies as it defines future optical access schemes. R&D work, new modulation schemes and component developments including silicon photonics will all be assessed as to their suitability for future optical access schemes.
Meanwhile, FSAN says it will review its roadmap on a yearly basis and amend it as required.
See Part 1: XGS and TWDM passive optical networks, click here