Four major application areas are driving next-gen PON development and standardization.
FTTBuilding for multi-dwelling units (MDUs) – In these deployments, next-gen PON would provide more bandwidth to be shared among the units in the building.
Enterprises – Next-gen PON would provide enterprises with more upstream bandwidth, supporting video conferencing and cloud-based file backup, for example.
MBH – Next-gen PON supports the growth in mobile traffic that needs to be backhauled along with backhaul support for VDSL2 vectoring and g.fast micronodes.
Fronthaul – The use of PON for fronthaul becomes an option with TWDM PON supported by a point-to-point fiber overlay on a dedicated wavelength. In the future, PON equipment vendors believe that fronthaul could be supported as a dedicated wavelength within a TWDM PON optical line terminal (OLT). Fronthaul refers to the connection between disparate radios to the centralized controllers via CPRI (common public radio interface) thereby supporting cloud-based radio access networks (C-RANs), for example.
Currently, the major drivers of next-gen PON are to serve enterprise subscribers and MBH. FTTH is becoming the norm in the majority of FTTx deployments due to improvements in the flexibility and size of fiber cabling along with operational issues and costs associated with FTTBuilding. The use of PON for fronthaul is still a new application.
Next-gen EPON – status, standard, ecosystem, and deployments
The IEEE ratified 10G EPON (802.3av) in September 2009 with two variations:
10G EPON symmetrical – supporting 10G downstream and upstream
10G EPON asymmetrical – supporting 10G downstream and 1G upstream.
10G EPON was designed to coexist with 1G EPON and to provide backward compatibility with 1G EPON. For example, 10G EPON and 1G EPON can operate on the same ODN, enabling CSPs to upgrade specific subscribers to 10G while maintaining other subscribers at 1G.
The 10G EPON ecosystem is robust and includes laser vendors, optical interface chip vendors, bidirectional optical subassembly (BOSA) and transceiver vendors, media access control (MAC) chip vendors, and equipment vendors. China Telecom has tested and shown interoperability at both the component and equipment levels.
10G EPON equipment is shipping, although volumes are well below original forecasts. Deployments include FTTBuilding MDUs and non-FTTH applications, such as enterprises and MBH. Enterprise services and MBH are the leading applications for 10G symmetrical EPON. CSPs deploying 10G EPON include traditional telcos, such as China Telecom, and cable operators, such as Bright House Networks in the US.
EPON component and equipment vendors along with CSPs have begun to discuss NG-EPON options beyond 10G via the IEEE 802.3 NG-EPON Ethernet Working Group.
Next-gen GPON – status, standard, ecosystem, and deployments
The ITU, through the FSAN (Full Service Access Network) Next-Generation PON (NG-PON) Task Group, has established standards for next-gen GPON.
XG-PON1 (part of NG-PON1) – Provides asymmetrical speeds of 10G downstream and 2.5G upstream as outlined in the ITU standard G.987, which was ratified in 2010.
TWDM PON (part of NG-PON2) – Combines the dedicated wavelength approach of WDM PON with GPON’s support for multiple subscribers on each wavelength. The standard for TWDM PON is expected to be completed in the first half of 2015. TWDM PON provides four or more wavelengths per fiber, each of which is capable of delivering symmetrical or asymmetrical bit rates of 10G or 2.5G.
XG-PON1 was designed to coexist with GPON on the same ODN, allowing subscribers to be upgraded incrementally. Solutions using the XG-PON1 standard have been developed by leading PON component and equipment vendors. Several CSPs have trialed XG-PON1 equipment, but there have been very few commercial deployments to date. Lack of significant demand for XG-PON1 will likely continue, as GPON provides sufficient bandwidth for initial MBH and SMB applications.
FSAN’s participants analyzed a number of approaches to NG-PON2 including WDM PON. After significant cost and operational analysis, they chose TWDM PON. With WDM PON, each customer is assigned a dedicated wavelength, offering bandwidth and performance advantages, but equipment and operational costs are high when compared to the point-to-multipoint architecture of TWDM PON.
TWDM PON is likely to be chosen by CSPs as the next-gen GPON solution due to its overall bandwidth capacity, ability to separate traffic types by wavelength, and pay-as-you-grow wavelength and bandwidth flexibility. In addition, TWDM PON, unlike GPON and XG-PON1, can easily support the equivalent of regulation-mandated LLU (local loop unbundling) in FTTx networks.