Insights into Next-Generation PON Evolution

Bandwidth Trend

More and more feature-rich services are being created, and people’s expectations for quality of experience (QoE) are increasing. The rapid growth of P2P, HDTV, 3DTV, interactive 3D, Internet of things, and cloud computing has created a huge demand for bandwidth, and this means new challenges to broadband deployment and operation. 

To be more competitive, operators have begun to introduce new technologies into their networks and transform them with innovative terminal-pipe-cloud architecture. They are shifting their focus from network and connection to service provision and user experience.

Informa predicts that the volume of Internet traffic worldwide will grow sevenfold between 2010 and 2015. This traffic growth is in line with Moore’s Law. According to Nielsen’s Law, the bandwidth available to users increases tenfold every five to six years. So it is inevitable that fiber will need to be offered to end-users. China Telecom devised a “fiber in copper out” strategy because optical fiber is considered the most desirable access media for solving the last mile bandwidth issue.

Technology Options for PON Evolution

Passive optical network (PON) is an optical-fiber-based network architecture that can provide much higher bandwidth in the access network compared with traditional copper-based networks. PON evolves from A/B PON, GEPON, and GPON to 10G EPON, XG-PON1, and NG-PON2.

 GEPON and GPON were first proposed by EFMA/IEEE and FSAN/ITU-T. GEPON evolves to 10G EPON and then to NG-PON2, and GPON evolves to XG-PON1 and then to NG-PON2. NG-PON2 includes TWDM-PON, WDM-PON, and OFDM-PON. 10G EPON standards were released with IEEE 802.3av in September 2009. XG-PON1 was standardized by ITU-T in June 2010 as the G.987 family of recommendations. NG-PON2 standardization is still underway.

New services and applications have increased the demand for bandwidth at the access layer, and this demand for bandwidth has grown from 100 Mbps (DSL), 1 Gbps (GE/GPON), and 10 Gbps (10G PON) to 100 Gbps (NG-PON2).

Key features of NG-PON include:

• flexibility. Flexible bandwidths meet various service needs and can be achieved with multiple wavelengths, which increase bandwidth through overlapping, or a single wavelength that uses modulation to widen the bandwidth. NG-PON can accommodate leased wavelengths, leased lines, mobile backhaul, WLAN backhaul, and video overlay while guaranteeing QoS and security.    
• smooth evolution. NG-PON is future-proof and can be upgraded smoothly without the need for drastic changes.
• large split ratio. The maximum power budget for NG-PON is more than 28db, and its split ratio is more than 1:128.
• wide coverage. The distance between OLTs and ONU/ONTs is more than 60 km to 100 km.
• power splitter. Power splitters are used to extend the distance covered by OLTs.
• colorless ONU. Colorless ONUs are a basic requirement for operators to deploy commercial NG-PON.
• low cost. Existing network elements, including OLT, ODN and ONU, are fully used to save capex. ODN can be reused to support an incremental next-generation upgrade. Legacy OLT/ONU can coexist with NG-PON OLT/ONU.

There are three mainstream technology options for NG PON2: TWDM-PON, WDM PON, and OFDM-PON. ZTE has been actively developing all of these.

TWDM-PON is a hybrid of TDM/WDM-PON. It has good compatibility with TDM PON (EPON and GPON). In March 2010, ZTE announced a WDM/TDM PON prototype and released a colorless transceiver ONU.

There are many variants of WDM PON, including tunable DWDM PON, injection-locked DWDM PON, tunable UDWDM PON, and coherent UDWDM PON. ZTE demonstrated its tunable DWDM PON system at the Broadband World Forum 2010 in Paris.

OFDM-PON offers excellent performance and can bear multiple services. However, it doesn’t coexist well with other PONs, and the cost of ONU in OFDM-PON is high. In addition, OFDM-PON has a long industrial cycle and low optical power. ZTE has led research on key OFDM-PON techniques in China’s “863” program and “tri-network convergence” project.

TWDM-PON has advantages over WDM-PON and OFDM-PON. In the latest FSAN meeting held in April 2012, TWDM-PON was viewed as the preferred option for NG-PON2. TWDM-PON can coexist with video overlay, and XG-PON1, although coexistence with XG-PON1 is not mandatory. Wavelength bands and architecture need to be defined to support hybrid WDM-overlay deployment.

10G PON: The Basis of NG-PON2

Some operators have built their broadband networks on DSLAM and MSAN, and some have adopted 1G PON (GEPON or GPON) for FTTx deployment, which provides bandwidth per user of less than 50 Mbps. However, since 2010, user bandwidth has increased to between 100 and 300 Mbps. GEPON and GPON can no longer meet these growing bandwidth needs, and this has given rise to NG-PON. 10G PON provides bandwidth of more than 100 Mbps to each subscriber in either symmetric or asymmetric upstream/downstream links. 10G PON is similar to 1G PON and supports zero-touch management and flexible networking. It is also highly secure and not inexpensive to deploy.

10G PON includes 10G EPON and XG-PON1, and the standards for these have been released. NG-PON2 standards are still being researched and will be discussed and implemented in the years to come. NG PON2 is not expected to be commercially available until 2018 whereas 10 GPON is expected to be widely deployed between 2013 and 2018.

ZTE’s R&D Work on Next-Generation PON

ZTE is a leading FTTx provider and a member of FSAN and IEEE. The company has been keeping up-to-date with developments in NG-PON standards, management and operation, ODN, and broadband detection. ZTE can provide end-to-end and turnkey solutions for FTTx deployment. ZTE has received national funding for its large-capacity TWDM PON access and SMILE OAN architecture, and has led research on hybrid PON standards in CCSA.

Milestones of ZTE’s NG-PON Development

2008–2010: ZTE contributed to creating optical access standards and submitted the highest number of XG-PON and NG-PON2 proposals to FSAN.

March 2009:    ZTE was the first vendor to launch a tunable laser-based WDM PON system.

March 2010:    ZTE announced a WDM/TDM PON prototype and released a colorless transceiver ONU.

May 2010: ZTE released a XG-PON1 prototype.

May 2011: ZTE XG-PON1 achieved good results in an interoperation test conducted by China Telecom.

September 2011: ZTE was the chief editor of an OFDM-PON white paper produced with FSAN Group.

October 2011: ZTE XG-PON1 achieved good results in an interoperation test conducted by FSAN.

December 2011: ZTE won an exclusive three-year grant from China's 863 Program and led research on ultra 100G WDM/TDM hybrid PON standards in CCSA.