Active Ethernet is one popular way to deliver massive amounts of bandwidth to subscribers over fiber and is a major contender for Fiber to the Home (FTTH) based broadband Internet rollouts.  In the US, it is more popular with the smaller telcos than with the larger ones.  It competes with PON in all it various flavors (EPON, 10G EPON, BPON, GPON, WDM PON, etc.) and with what is called Point-to-Point (P2P) Ethernet or Active Fiber.

Point-to-Point (P2P) Ethernet/Active Fiber

P2P Ethernet/Active Fiber is just 100Mbps or 1Gbps fiber Ethernet delivered directly from a Central Office (CO).  Active Ethernet is essentially P2P Ethernet/Active Fiber delivered from aggregation equipment installed outside the CO.  An Active Fiber/P2P Ethernet network is shown below with the Optical Line Terminal (OLT) installed in the CO and Optical Network Terminals (ONTs) installed at each subscriber’s house.

Active Ethernet

The essentials of an Active Ethernet network are shown in the diagram below.  Ethernet aggregation equipment is installed in the CO and in the OutSide Plant (OSP).  An Ethernet Optical Network Terminal (ONT) is installed at each customer premises.  The Ethernet aggregation device that connects directly to ONTs is a temperature-hardened Ethernet switch and called the Optical Line Terminal (OLT).

Active Ethernet is specified in IEEE (US) standard 802.3ah for Ethernet in the First Mile.

Optics

Two single fiber and two dual fiber interfaces are commonly used in Active Ethernet networks as described below.

Dual fiber (not bad, less expensive transceivers but lots of fiber)

• 1000BASE-LX – 1 Gbps over two single mode fibers (1310 nm in both directions)
• 100BASE-LX -100 Mbps over two single mode fibers (1310 nm in both directions)

Single fiber (better, same rates, half the fiber, but more expensive transceivers)

• 1000BASE-BX – 1 Gbps over one single mode fiber (1490 nm from network to subscriber and 1310nm from subscriber to network)
• 100BASE-BX – 100 Mbps over one single mode fiber (1490 nm from network to subscriber and 1310nm from subscriber to network)

Advantages and Disadvantages

What are the advantages of Active Ethernet?  1) Large bandwidth is available directly and unshared to each subscriber, at least 100Mbps and perhaps 1Gbps on each Optical Network Terminal (though shared on the uplinks to the aggregation equipment), 2) It is easier to manage because a network transceiver (in the ONT)  is dedicated to each subscriber, and 3) It is a relatively mature technology with a variety of equipment choices.

What are the disadvantages of Active Ethernet? 1) The name indicates a disadvantage in that “active” electronics must be deployed in the outside plant (OSP), and OSP electronics are more expensive to deploy and maintain than CO electronics, and 2) Active Ethernet imposes the cost of a network transceiver dedicated to each subscriber.

Lightwave has an article comparing Active Ethernet to PON written by World Wide Packets, now part of Ciena.

© 2009, The Product Group LLC. All rights reserved.

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