Evolving passive optical networks (PONs) demand FPGA design flexibility

By Nilam Ruparelia, Altera
Programmable Logic DesignLine -- (03/12/08, 01:35:00 PM EDT)

Overview

FPGA technology, low cost optics, and a passive architecture have made significant contributions to passive optical networks (PONs) and to the evolution of these networks. System OEMs continue to discover that FPGAs deliver both technical design and economic benefits, especially at the central office (CO) infrastructure end of the network side.

Prior to 2002, lower-performance FPGA generations served primarily as prototyping tools. Today's FPGAs are high performance, feature rich, and well suited to meet growing PON design requirements. Plus, FPGAs that offer lower design costs, flexibility, and scalability are the linchpin for turbo-charging the PON market.

A PON is a point-to-multi-point (P2MP) fiber to the premises (FTTP) network topology, which may also be defined as fiber to the curb (FTTC) and fiber to the home (FTTH). Either FTTP or CPE (customer premises equipment) is used in the PON definition. Un-powered or passive optical splitters are used so that a single optical fiber serves multiple premises; usually 32, but as many as 64. A PON comprises an optical line termination (OLT) at the service provider's CO and a number of optical network terminals (ONTs), also known as optical network units (ONUs) going to the premises.

1. DSL and PON topologies side-by-side.

Downstream OLT signals are broadcast to each ONT sharing a fiber. Current PON standards have defined downstream data rates up to 2.5 gigabits per second (Gbps). Upstream signals are combined using time-division multiplexed (TDM) access. Compared to digital subscriber line (DSL) or cable, PONs offer an unparalleled bandwidth advantage for high-speed triple play services (voice, video, and data).

According to Infonetics, PON subscribers are expected to grow dramatically at a compound annual growth of 150 percent through 2010 in North America and Asia Pacific. Gigabit PON (GPON) is making strong headway in North America, while Ethernet PON (EPON) is mostly used in Japan. Japanese government subsidies are helping to grow the PON market substantially year to year, while EPON and GPON is being carefully weighed in China.

Broadband PON (BPON) or International Telecommunications Union (ITU-T) G.983x is the prevailing U. S. PON standard. It features a maximum downstream data rate of 622 megabits per second (Mbps) and 155 Mbps upstream. Passive optical splitters installed in the fiber allow up to 64 subscribers to use the line. This year, GPON or ITU-T G.984, an evolution of BPON, is expected to enter greater numbers of U. S. premises. It supports TDM and packet data with data rates of up to 2.5 Gbps downstream and 1.24 Gbps upstream. Key GPON advantages are support of switched digital video and native TDM voice without having to add IP.