EPON becomes long reach

A controller chip that extends the reach and subscriber count of an Ethernet passive optical network (EPON) is now available from Teknovus. The device, dubbed the TK3401, boosts EPON’s reach to 100km while the subscriber count is increased from 64 to a maximum of 256.

“Rural [PON deployment] is a tough proposition”

Barry Gray

Moreover, the TK3401 supports up to four such EPONs. The chip does not require changes to EPON’s optical transceivers although wavelength division multiplexing (WDM) transceivers are needed for the greater reach.

The TK3401 sits within what Barry Gray, director of marketing for Teknovus, calls the Intelligent PON Node (IPN). The IPN resides 20km from the subscriber’s optical network unit (ONU), where the PON’s optical line terminal (OLT) normally resides.

On one side of the IPN platform are sockets for up to four EPON OLT transceivers that support the PONs. On the other side are four SFP WDM transceivers that communicate with the central office up to 80km away and where the OLT platform is located. The OLT line card instead of using OLT optics uses WDM transceivers also in the SFP form factor. As such the line card does not require any redesign (see diagram).

Up to four point-to-point fibres can be used to connect the PONs’ traffic to the OLT, or a single fibre and up to 8 lambdas with coarse WDM (CWDM) technology to multiplex four PONs onto a single trunk fibre.

The 256 subscribers are achieved using a PX20+ specified optical transceiver. “It has a 28dB link budget such that going through 8 splitter stages is still sufficient for 2km distances [from the ONUs],” says Gray. “This is ideal for multi-dwelling unit deployments.”

Besides the pluggable optics, the IPN design includes the TK3401, a field programmable gate array (FPGA), and a flash memory.

The TK3401 comprises an EPON ONU media access controller (MAC), microprocessor and on-chip memory. The MAC registers the IPN with the central office OLT to set up remote IPN management and configuration communication links. The on-chip memory holds the firmware that configures the FPGA on start-up. The FPGA implements a crossbar switch to connect traffic from any of the EPONs to any of the WDM ports.

The IPN approach offers other advantages besides the 100km reach and increased subscriber count. It has a power consumption of 20W which means it can be powered from such locations as a telegraph pole. As the PONs are first populated, all four PONs’ traffic can also be aggregated into a single WDM link OLT port, with OLT ports added only when needed. In turn a fibre link can be used for protection with a sub-100ms restoration time.

However, unlike long reach PON or WDM-PON which also offer a 100km reach, the Teknovus scheme still requires the intermediate network node. The node is also active as it must be powered.

Teknovus claims it has strong interest from its IPN-based EPON architecture from operators in Japan and South Korea, while interest in China is for rural PON deployments. “Rural [PON deployment] is a tough proposition for service providers,” says Gray. “There is not the subscriber density and it is more expensive; the same is also true for mobile backhaul.”

The company is demonstrating the IPN to customers.

Click here for Teknovus' IPN presentation and White Paper