Electronic Design

GPONs Bring Triple-Play Service To Consumers—Fast

The BL2000 series from Broadlight implements a 2.5-Gbit/s optical broadband system for consumer services. With these chips, new passive optical networks (PONs) can go directly to the faster gigabit-PON (GPON) standard to provide even faster service to more users.

PONs are data networks implemented with optical fiber but no intervening electrical (active) transceivers. This lowers the cost of optical networks and makes short-range (20 to 60 km) broadband connections using fiber practical and affordable.

Already, PONs are widely used in Asia and some parts of Europe. SBC and Verizon both are testing and installing PONs in selected parts of the U.S. It won't be long before triple-play services (TV, data, and Voice over Internet Protocol) can be offered over very high-speed PONs.

The prevailing PON standard in the U.S. is broadband PON (BPON), also known as ITU-T standard G.983.x. It features a maximum download data rate of 622 Mbits/s. Passive optical splitters are installed in the fiber to allow up to 64 subscribers to use the line. The GPON standard ITU-T G.984 bumps the speed options to 1.244 and 2.488 Gbits/s and is backwards-compatible with BPON.

Also, the GPON standard provides greater speed and a higher split ratio than the competing EPON or Ethernet PON, which maxes out at 1.25 Gbits/s and a 1:32 split ratio. GPON offers a huge cost savings over EPON—not to mention the greater capacity—for this reason.

On the carrier side of the system, known as the optical line terminal (OLT), the Broadlight BL3000 MAC FPGA implements the full ITU-T G.984 standard. It provides for operation in the GPON Encapsulated Mode (GEM), which permits 64 subscribers using 155-Mbit/s time-division multiplexing (TDM) data.

The Broadlight BL2000 handles all of the operations on the subscriber side, which is called the optical networking terminal (ONT). This chip is available in several versions to handle single-family units, small business units, and multi-dwelling/multitenant units. To handle T1/E1/J1 services, designers add the Broadlight TDM/GEM FPGA chip (see the figure).

Additionally, Broadlight supplies the PONmaker software. It provides full source code, including host API, hardware abstraction layer, and OS abstraction layer. It handles full ONT control with ranging and activation, provisioning, AES control, dynamic bandwidth management (DBM), alarms and performance monitoring, and fault handling as well.

The company also supplies optical transceivers for the PONs. Normally, 1310- and 1490-nm lasers and photodiodes are used for upstream and downstream full-duplex communication on a single-mode fiber. A third wavelength of light at 1550 nm can be added to accommodate a community-antenna TV overlay.

All of the Broadlight products will be available by December 2005. Targeted price for the BL2000 is less than $20 in very high volume.


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