Electronic Design

2.5/10-Gbit Ethernet Switches Slip Into PON Systems

Gigabit passive optical networks (GPONs) are a growing niche in delivering broadband services to homes and small businesses. Yet their growth has created a need for more and better switch chips to build scalable networking equipment that can handle an increasing number of subscribers. The latest Ethernet switches in Fulcrum's Focal-Point line fill this need.

GPON, an ITU standard for passive optical networks, uses no active devices in the network. Downstream signals on 1490 nm at a rate of 2.5 Gbits/s are split into 32 or 64 separate data-rate streams in a passive splitter before reaching subscribers' homes. This arrangement provides rates of 30 to 100 Mbits/s up to a maximum reach of 20 km.

A central office called the optical line terminal (OLT) delivers the downstream. The subscriber's unit—the optical network terminal (ONT)—can deliver an upstream signal on the same passive fiber on 1310 nm. The GPON encapsulation mode (GEM) protocol permits standard telecom time-division multiplexing (TDM), cell, or packet data to be transported. The carrier's OLT will require multiport line cards to deal with the increasing number of subscribers while controlling costs.

Configured for four-port OLT line cards, the FM2103 offers four 2.5-Gbit/s Ethernet ports for access connections and two 10-Gbit/s Ethernet XAUI ports for backbone connections (see the figure). The FM2104 is designed for eight 2.5-Gbit/s OLT ports and two 10-Gbit/s XAUI ports.

Both have flexible built-in header processing for Ethernet-to-GPON internet-working, so they can parse the GPON specific packet header. While specifically targeting the GPON opportunity, these chips also fit line cards for carrier-grade Advanced Telecom Computing Architecture (ATCA) communications equipment.

The patented Nexus Terabit Crossbar and RapidArray Packet Memory lie at the core of these devices. Nexus uses Fulcrum's asynchronous (clockless) event-driven logic to deliver more than a terabit per second of non-blocking throughput with 3 ns of fall-through latency. RapidArray combines the Nexus crossbar's super-fast data path with standard foundry state bits to deliver packet memories with twice the throughput of commercial memories while maintaining comparable density and yield.

Both chips come in a 32- by 32-mm 897-ball ball-grid array. The FM22103 costs $150 and the FM2104 costs $175 in volume. Samples are available now.

Fulcrum Microsystems Inc.

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