What's in a node?

The size of nodes in a fiber network is based simultaneously on a network's history and its future

In building fiber-to-the-node networks, telecom service providers are relying extensively on their experience with outside plant engineering while future-proofing their networks for what they know will be bandwidth-intensive applications.

For example, AT&T is putting most of the nodes for its Project Lightspeed network at the existing service area interface (SAI) because that makes the most sense in a carrier service area-designed network, said Matthew Wallace, executive director of advanced access technologies for AT&T. The CSA design standards are based on Bellcore and Bell Labs engineering standards that go back decades. Typically, AT&T's nodes serve around 300 homes and deliver the 25 Mb/s bandwidth to each home required for U-verse IPTV service, including high-definition and standard-definition streams.

“If you look at AT&T's progression of DSL deployment, where we initially put a DSLAM was at a place in the CSA-designed network where lots of [outside plant] cables come together,” Wallace said. At first that was a central office; later it was at the CSA, where AT&T added fiber as part of Project Pronto and then its next-generation digital loop carrier deployment, he said.

“The next step is FTTN at the service area interface or fiber distribution interface because that's where we have a cross-connect box that is already part of the copper telephony network,” Wallace said. “We are placing a DSLAM near there to get at where copper cables are already designed to come together in large numbers.”

Qwest has deployed fiber to the FDI as well, giving it nodes of about 350 homes in about 90% of its local territory, said Pieter Poll, chief technical officer for Qwest.

“We have a very clean plant,” Poll said. “All of our cross-points are at distribution areas, not carrier serving areas. At first that was a disadvantage because our fixed costs were high, but now we have these 350 home nodes, and we can bring in Gigabit Ethernet feeds or multiple GigEs” over fiber.

It makes sense to follow the evolution of the outside plant, said Steve Kemp, senior director of product marketing for broadband access for Alcatel-Lucent.

“Because the copper plant has been laid out a particular way for so many years, probably nothing is going to change super-fast,” Kemp said. “But the first order of the day is to figure out what you are going to sell.”

The choice of application is determining many service providers' node-size decisions, said Ray Savona, vice president of field marketing for Calix, a maker of fiber access gear.

“I would contend you start with what services you want to offer,” he said. “If you start with a 10 meg data service, then you look at what kind of feeder you have, then you do the statistical analysis and determine what kind of over-subscription you can do based on the service you want to offer.”

Cable companies have beefed up their delivery by shrinking node size in their hybrid fiber/coax networks, but that is not the next logical progression for telcos. Both AT&T and Qwest plan to use pair-bonding to increase the amount of bandwidth they can deliver.

“Shrinking node sizes is typical with cable but doesn't work as easily in a CSA-designed telephone network,” Wallace said. “Once you get past that SAI box that is already in place in the network, the cables start branching out much finer and much smaller.”

SAIs tend to be at the edge of a neighborhood, he said. Going deeper in drives up costs dramatically and disrupts customers significantly as well, making FTTN less economically viable, Wallace said.