PON evolution and future FTTH market prediction: XG-PON1

“Most modern GPON ONTs have an integrated filter to eliminate interference from XG-PON1 wavelengths.”

Next-generation PON Evolution: XG-PON1

Contributors: José Salgado, Rong Zhao, Nuno Monteiro, and Pauline Rigby

  The XG-PON1 approach, defined by ITU-T G.987 for near term deployment, operates with existing optical distribution networks and equipment. It provides 10 Gbps of shared downstream bandwidth, combined with 2.5 Gbps of upstream bandwidth.

Optical fibreSingle fibre transmission, compliant with ITU-T G.652
Wavelength planUpstream 1260nm to 1280nm / downstream 1575nm to 1580nm
BandwidthDownstream: Up to10Gbps / Upstream: Up to 2.4Gbps Support for dynamic bandwidth allocation (DBA) Full QoS and traffic management
Nominal line rateUpstream: 2.48832 Gbps / downstream: 9.95328 Gbps
Media access control layerUpstream: TDMA / Downstream: TDM Forward error correction with scrambled NRZ line encoding
Optical power budgetBetween 29 dB and 35 dB
Split ratio1:32, 1:64, scalable up to 1:256
Fibre distanceDifferential distance of 20 km or 40 km.
Logical Distance of up to 60 km.
SynchronizationEnhanced timing and time-of-day synchronization for mobile backhaul applications
Enhanced securityStrong mutual authentication; Authentication to protect the integrity of the PON management messages and the PON encryption keys.
Power saving featuresReduce the load during power failures (so batteries last longer), by turning off inactive user network interfaces (UNI) Deactivating the transmitter for routine transmissions (“dozing”) Sleep mode, in which the ONT deactivates both its transmitter and receiver when the user has no activity (“sleeping”)

  XG-PON1 inherits the framing and management from GPON. Full-service operation is provided via higher data rate and larger split while keeping a flattened network structure – adding more features and capacity without adding complexity to the optical distribution network.

  Driven by the 10G optical transceiver market and the available bands for achieving legacy compatibility, FSAN selected the XG-PON1 downstream wavelength of 1575nm and upstream wavelength around 1270nm. For GPON and XG-PON systems to coexist on the same network requires the addition of a wavelength coupler located at the central office, which has already been defined as WDM1r in ITU-T G.984.5.

ITU-T G.987 wavelength plan

ITU-T G.987 wavelength plan

  GPON class B+ defines a 28dB power budget. Due to the addition of the WDM1r combiner, some slight additional loss was added to the XG-PON1 power budget, resulting in an equivalent 29 dB budget. Additionally, XG-PON1 specifies 31, 33, and 35 dB options for the power budget.

  A potential barrier to the deployment of GPON and XG-PON1 on the same outside plant is the existence (or non-existence) of wavelength blocking filters at the optical networking terminals (ONTs) in the customer premises. Most modern GPON ONTs have an integrated filter to eliminate interference from XG-PON1 wavelengths. However, older installed ONTs won’t have such a filter. Service providers with older ONTs deployed will have to install filters at the ONT locations to enable GPON and XG-PON1 co-existence.

  For configuration, operation and maintenance, GPON and XG-PON use the same, generic Optical network unit Management and Control Interface (OMCI), specified in ITU-T G.988.

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