A Remote Possibility

Posted 10/15/2001

A Remote Possibility
PON Vendors Target DSLAM Aggregation

By Paula Bernier

Fiber-to-the-user isn't the only opportunity for passive optical networks (PONs). Recently DSLAM aggregation has emerged as another key application for PON.

In this scenario, PON is used to carry signals over fiber from the central office (CO) to a remote terminal where the service is passed off onto the copper infrastructure that goes to the user. Alloptic Inc., Quantum Bridge Communications Inc. and Terawave Communications Inc. already have introduced hardened PON devices for outside plant deployment in remote terminals, and NEC eLuminant Technologies Inc. has such a product in the pipeline.

"We think that will be one of the really interesting applications for this technology going down the road," says Jim Holley, senior vice president of marketing at NEC eLuminant.

Dilit Modi, senior product line manager at Terawave explains that putting DSLAMs in remote terminals can enable carriers to reach the approximately 90 percent of the people who otherwise would be too far from a CO to receive DSL. SONET is one way these carriers could connect their remote terminals back to the CO, he adds. But SONET costs twice as much as PON because SONET requires a dedicated DS3 for each DSLAM, he adds.

A DSLAM usually outputs around 10mbps as opposed to a constant 45mbps (which is the bandwidth of a DS3 connection), says Modi, so there's a lot of idle bandwidth in the SONET scenario.

Also, carriers would require a dedicated DS3 from the add/drop multiplexer at the CO to the ATM switch. But with PON, a carrier can put 10 or 12 hardened optical remote terminals in the field, which also act as add/drop muxes. Those devices can aggregate the signals from multiple DSLAMs onto a single OC3 or OC12 and send it directly to the ATM switch, Modi explains.

He says Terawave's PON product does dynamic bandwidth allocation so the carrier can put as many as 40 DSLAMs over the same fiber, because not all 40 DSLAMs have peak output at the same time.

NEC eLuminant's Holley says putting DSL into an ATM format as soon as possible enables ILECs to benefit from ATM's statistical gains.

"That's kind of the rationale for using ATM PON for DSLAM deployments," Holley says. "They can convert DSL to ATM right where the DSL terminates, which is going to be in a cabinet or some kind of device in the outside plant."

Plus, by using PON rather than SONET, carriers get the benefit of a passive network, which doesn't require separate power (batteries and AC power devices required by SONET can be expensive to deploy and maintain), Holley adds.

Quantum Bridge, with an undisclosed ILEC, planned to go into trials this summer at NFOEC with a hardened 622mbps system with DS3 interfaces for DSLAMs. Meantime, Terawave, expects this fall to go into a lab trial for its hardened PON product with an ILEC.

Last July at NFOEC, Alloptic introduced a hardened optical network unit (ONU), called the curbG.E.A.R. ONU. But, unlike most PON products on the market, the Alloptic product is based on Ethernet as opposed to ATM technology. Because DSLAMs are based on ATM for transport, Burnie Atterbury, senior director of product marketing, says the Alloptic products could support DSLAM aggregation through a clear channel application on its PON, which would require a piece of CPE to encapsulate ATM and put it on a lambda on the PON. Alloptic had not begun running any DSLAM aggregation field trials at press time.

NEC eLuminant is looking at augmenting its product line next spring with a hardened optical network terminal using an ATM-based DS3 interface. Holley says these devices--PON optical network terminals (ONTs, likely will be integrated with remote DSLAMs into a single product. NEC eLuminant is working with DSLAM vendors to deliver such an integrated product in mid- to late-2002, he adds.

But, Holley says, regulatory concerns could be a significant barrier to the widespread adoption of remote terminal DSLAMs. The Federal Communications Commission (FCC) has not issued rules regarding how remote DSLAMs or remote access should be unbundled, says Holley. Because of this, the RBOCs are waiting for an FCC ruling before they until they invest in DSL and related equipment for remote terminals.

"A remote cabinet is very different animal than a CO, where it's easy to open it to competitors and secure parts of it for competitors' access," says Holley.

These remote cabinets are small, and so they don't have separate access for competitors.

Also, outside plant cabinets have heat output and space limitations on the amount of equipment they can house, Holley says.

"So it's not practical for [the FCC] to say 'well the CLECs should have access to these cabinets just like ILECs do,'" says Holley.

Source: Terawave Communications Inc. (www.terawave.com)