On the face of it, passive optical networks (PONs) and digital subscriber line (DSL) services couldn't be less compatible. While both are low-cost, high-speed techniques for delivering data to homes and offices, PONs run over fiber and DSL uses copper connections. (See PONs: Passive Aggression for more on PONs.)

But industry sources say there's a new dialectic at work, making PONs and DSL the ideal partners in building out next-generation carrier nets.

Here's why: Recent U.S. regulatory rulings from the Federal Communications Commission (FCC) are giving ILECs (incumbent local exchange carriers) an incentive to get DSL services up and running on a grander scale. As a result, DSL services are expected to explode in the near future. And that's leading carriers to expand the buildout of their networks to support DSL.

PONs will reduce the costs of expansion. Specifically, carriers say they'll use PONs to extend bandwidth cheaply from the central office to multiple outdoor vaults, where telecom gear is linked to last-mile copper or fiber. PONs would let carriers use just one fiber from the central office to deliver bandwidth to up to 32 remote outdoor vaults. Inside each vault, the PON link would be hooked to a DSL access multiplexer, which in turn could pass bandwidth over existing copper wire to homes and businesses.

"PONs are definitely going to be the fastest, cheapest way for incumbents to expand DSL services," says Tom Nolle, president of CIMI Corp. http://www.cimicorp.com, a consultancy. He says the link between DSL and PONs is already happening in the network of SBC Communications http://www.sbc.com (NYSE: SBC).

According to that carrier's Web site, over 4,000 outdoor vaults are going in this year. They'll be populated by Litespan-2000 and -2001 Digital Loop Carrier DSL devices from Alcatel SA http://www.alcatel.com. Nolle says sources at Alcatel told him that many of those outdoor vaults will be fed by PONs--also supplied by Alcatel. "The Litespan-2001 has been upgraded specifically to handle PON feeds," he says.

Neither Alcatel nor SBC would confirm the use of Alcatel PONs in SBC's network at press time.

Other PON vendors are seeking outside partners. Quantum Bridge Communications Inc. http://www. quantumbridge.com and NEC Eluminant Technologies Inc. http://www.eluminant.com say that they're in talks with DSLAM vendors. And on June 5, Marconi Corp. PLC http://www.marconi.com (LONDON: MNI), which has confirmed it is developing a PON product, announced it will resell DSL gear from Copper Mountain Networks Inc. http://www.coppermountain.com (Nasdaq: CMTN).

At least some vendors hope the partnerships will result in new products. "We are in discussions with all the leading DSLAM vendors about putting PON terminations in their equipment," says Jim Holley, senior vice president of marketing at NEC Eluminant.

Neither NEC Eluminant nor Quantum Bridge would name whom they're talking to.

-- by Mary Jander, senior editor, Light Reading (http://www.lightreading.com)