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By goodvin | 09 November 2023 | 0 Comments

Development Trends of PON

Development Trends of PON

Passive optical networks (PON) have evolved tremendously over the past decades to become the preferred fiber access network architecture. This article explores the major advances in PON technology covering transmission rates, wavelength division multiplexing (WDM) capabilities and emerging next-generation PON standards.
Development of Transmission Rate
Early PON deployments supported 155 Mbps and 622 Mbps symmetrical speeds. Subsequently, standards were introduced for:
.Gigabit PON (GPON) – GPON supports 1.25 Gbps downstream and 622 Mbps upstream. Split ratios up to 1:64 are supported.
.10G GPON (XGPON) – An upgrade over GPON, it provides 10 Gbps downstream and 2.5 Gbps upstream. Supports higher splits up to 1:128.
.10G EPON – Provides 10 Gbps symmetric bandwidth over EPON architecture. Coexists with 1G EPON.
To achieve the high speeds, techniques like forward error correction, burst mode transmission, and dynamic bandwidth allocation were incorporated. Higher data rates enabled more bandwidth-intensive HD video and business services.
WDM-PON and Ultra Dense WDM-PON
WDM-PON allows multiplexing multiple wavelengths carrying independent 10Gbps data streams on a single fiber. This multiplicatively increases available capacity.
.Coarse WDM-PON – Spacing wavelengths on 20nm grid provides up to 80 km reach.
.Dense WDM-PON (DWDM-PON) – Closer wavelength spacing of 0.8 to 1.6 nm allows 100Gbps capacity over a single fiber.
.Ultra-dense DWDM-PON – Reduces channel spacing to 0.05-0.4nm using tunable lasers. Achieves Tb/s capacity over 40-60km.
Tunable components at ONU and dynamic wavelength allocation help optimize performance. The cost of wavelength control at ONU remains a challenge.
Introduction to Next-Generation PON Standards
New PON standards aim to meet growing bandwidth demands driven by 5G, fiber-to-the-home (FTTH), business services and gigabit Wi-Fi:
.NG-PON2 – Provides up to 80 Gbps capacity by stacking multiple 10 Gbps XGS-PON wavelengths. Supports tunable XFP lasers for flexible wavelength allocation.
.XGS-PON – Offers 10 Gbps symmetric speeds. Being deployed by operators due to its compatibility with existing GPON networks.
.25G EPON – Defines 25Gbps symmetric Ethernet PON carriered over a single wavelength. Reuses existing EPON fiber infrastructure.
.50G EPON – Under development, it will provide 50 Gbps symmetric capacity over EPON.
.50G-PON – In standardization by ITU-T, 50G-PON aims to deliver up to 50 Gbps capacity supporting a split ratio of 1:64.
.100G EPON – IEEE has formed a study group to enable 100 Gbps EPON in the future.
Next-gen PON will also incorporate SDN for dynamic bandwidth control, flexible Ethernet framing and slicing for 5G transport. The evolution of PON will enable fiber networks to stay ahead of emerging demands.
PON technology has constantly evolved from early 155 Mbps speeds to current multi-Gbps implementions. WDM-PON increases capacity further through wavelength multiplexing. Emerging 50G and 100G PON standards will enable fiber networks to support the rising performance needs of 5G, multi-gigabit access and business services. Operators are also enhancing PON with SDN and slicing to enable flexible allocation of network resources. The capabilities of PON will continue to expand to power ultra-broadband networks of the future.
Q1. What are the key differences between GPON and XGPON?
A1. The main differences are:
.XGPON provides 10 Gbps downstream and 2.5 Gbps upstream versus 2.5Gbps down and 1.25Gbps up for GPON.
.XGPON supports higher split ratios of 1:128 compared to GPON's 1:64.
.XGPON uses 10G XFP optical modules versus 2.5G SFPs in GPON.
.XGPON has higher reach of 60 km compared to GPON's 40km.
.XGPON incorporates more efficient GTC frame format versus older GEM for GPON.
.XGPON allows coexistence with GPON networks.
Q2. What wavelength bands are used in WDM-PON?
A2. WDM-PON typically uses the following wavelength bands:
.Downstream - 1480 to 1500 nm
.Upstream - 1550 to 1560 nm
.Overlay services - 1570 to 1610 nm
Ultra-dense WDM-PON can support over 100 channels from 1480 to 1620 nm band.
Q3. How does NG-PON2 provide higher capacity?
A3. NG-PON2 can deliver up to 80 Gbps capacity by bonding and stacking multiple XGS-PON wavelengths. Each XGS-PON offers 10 Gbps speed.
For example, stacking 4 XGS-PON wavelengths achieves an aggregate capacity of 4 x 10 = 40 Gbps. Advanced modulation schemes can further increase the data rate per wavelength to 25Gbps or higher.
NG-PON2 also allows tunable lasers that can dynamically allocate wavelengths based on traffic demand. This optimizes the available capacity.
Q4. What are the challenges in deploying 25G and 50G PON?
A4. Key challenges include:
.Higher optical module costs at 25G and 50G PON interface speeds.
.Increased fiber dispersion at 25Gbps and above requiring advanced modulation.
.Tighter optical power budget constraints due to faster speeds.
.Upgrading end-user ONUs to transmit high upstream speeds.
.Limited ecosystem and interoperability of 25G/50G PON equipment currently.
.Split ratio limitations due to higher PON port speeds.
Q5. Why is SDN important for next-generation PON?
A5. Software defined networking (SDN) enables the following benefits:
.Centralized control and dynamic bandwidth allocation instead of static configurations.
.Slicing PON capacity to tailor services for residential, business or mobile use cases.
.Simplified and open interfaces between OLT and ONUs for interoperability.
.Flexible Ethernet frame handling instead of fixed GEM port mapping.
.Managing integrated PON-AON optical distribution networks efficiently.
Overall, SDN provides the programmability and flexibility needed for future PON networks.
Keywords: PON, GPON, XGPON, NG-PON2, DWDM-PON, EPON, SDN, FTTH, Optical Access Networks

Recommended Reading: PON Network Testing and Maintenance

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