Passive Optical Network (PON) is a point-to-multipoint technology widely used for delivering FTTP (Fiber-to-the-Premise) solutions. Utilization of fewer active components in the network and sharing of feeder fiber makes it more cost effective than prevailing point-to-point and active network architectures. A typical PON deployment consists of an Optical Line Terminal (OLT) residing at a headend, hub or a central office facility. A passive splitter in the field typically splits the fiber into multiple segments that are connected to multiple Optical Network Terminals (ONTs) or Optical Network Units (ONUs) residing on customer premises. The PON technologies make use of Wave Division Multiplexing (WDM) technologies to share separate wavelengths on a single fiber in upstream and downstream directions. Typically downstream traffic from OLT to ONUs is broadcast in nature, whereas upstream traffic from multiple ONUs to OLT is combined using Time Division Multiple Access (TDMA) techniques. PON networks support speeds ranging from 100 Mbps to 10 Gbps depending on the choice of the particular technology used in the network. Also, depending on the specific implementation and technology, different split ratios (number of ONUs per OLT) up to 1:128 are supported.

PON technology has been heavily standardized from its inception. There are two main standards bodies, the Institute of Electrical and Electronics Engineers (IEEE) and the International Telecommunications Union (ITU), that have published extensive standards in the area of PON. Following is a brief synopsis of their work over the years.

IEEE

IEEE published the IEEE 802.3ah standard also known as Ethernet PON (EPON) or Gigabit Ethernet PON (GEPON). The GEPON specification is part of the Ethernet in the First Mile (EFM) initiative. This standard adapts Ethernet protocol (primarily a LAN technology) for MAN and WAN networks and supports both point-to-point and point-to-multipoint topologies. The transport protocol is native Ethernet and supports symmetrical speeds of 1 Gbps in both upstream and downstream directions. The standard also specifies a TDM based point-to-multipoint protocol for ONU to OLT upstream transport. Current typical deployments support a split ratio of 1:64.

GEPON technology has proven to be very cost effective as Ethernet optical components are very mature and are readily available at lower costs. Also, high volume deployments, particularly in Asian countries, has helped to drive economies of scale and bring prices further down. Familiarity with Ethernet technology from the LAN and data worlds makes it easier to understand and deploy GEPON.

Also in development (in draft form from the IEEE 10G Task Force) is the 803.3av 10GEPON standard that will support 10 Gbps rates in upstream and downstream directions. This standard is backward compatible with the existing GEPON standard and both technologies can be supported on a single fiber using multiple wavelengths.

ITU

ITU-T began with publication of the G.983 APON/BPON standards. These standards served as precursors to the ITU GPON standard. The transport protocol chosen was Asynchronous Transfer Mode (ATM) for its better Wide Area Network (WAN) transport characteristics and better traffic management for differentiated services. This standard support speeds of 622 Mbps (downstream) and 155 Mbps (upstream), and the supported split ratio is 1:32. This technology was more complicated to implement because ATM provisioning and traffic management is more complex than Ethernet/IP.

The current ITU standard that has replaced APON/BPON is ITU-T G.984 GPON. This standard supports multiple rates in both upstream and downstream with typical deployments at asymmetrical speeds of 2.5 Gbps (downstream) and 1.25 Gbps (upstream). The chosen transport protocol is GPON Encapsulation Method (GEM). It can support ATM, Ethernet and TDM native protocols. The currently supported split ratio is 1:64.

Due to lower economies of scale, GPON components are more expensive compared to GEPON. The ITU PON family of standards are more prevalent in North American FTTH deployments (U-verse and FioS).

Notes:
1. Maximum speeds specified. Some GPON chipsets implement a wide range of upstream/downstream rates.
2. Current typical chipset offerings. Implementations of 1:128 split ratios are on the horizon.

Node PON™

Aurora's Node PON currently employs the GEPON standard with symmetrical 1 Gbps bandwidth in both upstream and downstream directions. The Node PON design differs from traditional chassis-based PON architectures that are designed for telcos, one of the very important distinctions being its strategic placement of OLT in a cable node base. This strategic point of presence in the node is designed specifically with the typical MSO's network in mind.

Following are some of the advantages of a node-based access architecture.

• Overcomes 20 km distance limitation by pushing the OLT deep into the network. Supports over 100 km backhaul distances using DWDM technologies.


• High subscriber density with a single node can support up to a maximum 320 PON customers (5 OLTs supporting a 1:64 split per node).


• Flexible fiber backhaul architectures can be designed with options for (1) OLT daisy-chaining, (2) WDM techniques with one wavelength per OLT, and (3) OLT ring architectures for high availability.

Reference architecture for Node PON

Click on diagram to enlarge

Last but not the least, Aurora's Node PON is fully compatible with DOCSIS^®-based provisioning architectures. This design helps MSOs retain their existing investments in back-office NMS and OSS systems for subscriber management, billing and accounting services.

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