A passive optical network (PON) is a point-to-multipoint, fiber-to-the-premises (FTTP) network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises. Depending on where the PON terminates, the system can be described as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), or fiber-to-the-home (FTTH). A PON consists of an optical line termination (OLT) at the service provider's central office and a number of optical network units (ONUs) near end users. Typically, up to thirty-two ONUs can be connected to an OLT. Optical transmission has no power requirements or active electronic parts once the signal is going through the network. In a stand-alone system, a PON could deliver up to 622 Mbps downstream and up to 155 Mbps upstream to the user. Multiple users of a PON could be allocated portions of this bandwidth.

In PON, the process of transporting data downstream to the customer premises is different from transporting data upstream from the customer premises. Downstream data is broadcasted from the OLT to each ONT. Each ONT processes the data by matching the address at the protocol transmission unit header. There is a need to coordinate between the transmissions of each of the ONTs to the OLT in order to avoid collisions. Upstream data is transmitted according to control mechanisms in the OLT, using a TDMA (time division multiple access) protocol, in which dedicated transmission time slots are granted to each individual ONT. The time slots are synchronized so that transmission bursts from different ONTs do not collide.

Current Scenario
PON-based FTTP is already being rolled out, but at different rates and with technological variations, in different parts of the world. The main regions currently are Asia-Pacific, North America and, to some extent, Europe.

Japan is where the real FTTP action is happening, largely because of the government policies that help encourage broadband use, and competition. In Japan, Nippon Telephone and Telegraph (NTT) is planning to install PONs throughout its system, using equipment made by Lucent Technologies.

Other parts of Asia-Pacific-such as China, Korea, and Australia are in the early stages of FTTP deployment.

Motorola has also extended its ultra-broadband innovation with cable PON, a technology that delivers PON solutions customized to accommodate existing cable infrastructures. Cable PON, a unique cable-driven technology, delivers the business benefits of combined hybrid-fiber-coaxial (HFC) and PON network architectures.

Verizon have announced that it would soon begin deploying Gigabit passive optical network (GPON) technology that increases aggregate speeds on FTTP systems by four times downstream to the customer, and by eight times upstream, to support future enhancements to FiOS Internet services and FiOS TV.

In India, Freescale Semiconductor has launched the industry's first voice-enabled GPON. The company, along with Alcatel-Lucent, is facilitating the adoption of FTTH technologies by availing jointly developed GPON technology, and interoperability specifications to vendors of terminal equipment worldwide.

Market Growth
The market for PON hardware is forecast to grow sharply. Worldwide OLT and ONT PON equipment revenue reached $525 mn in 2004 and is projected to grow to $2.2 bn in 2008, with port shipments reaching more than 8 mn.

PON is an attractive solution for high-bandwidth access networks and also removes the need for expensive infrastructure upgrades. Currently, service providers of all shapes and sizes are pushing fiber deeper into their access networks to support the demand for video, online gaming, P2P networking, and other bandwidth-intensive applications and PON could be a solution for them.

Sandeep Budki
sandeepb@cybermedia.co.in

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