When it comes to fiber-to-the-premisses (FTTP) architectures, the telcos and other broadband operators now have a bountiful menu of options from which
to cholls. But those choices -some passive, others active- have their
own advantages and shortcomings.

The number of telcos and broadband operators deploying or testing fiber-to-the-premises (FTTP) networks is growing by the month. They may be uniform in the sense that the aim is to pull fiber to the customer home, but how they are going about it on the network is much more diffuse.

In fact, there is a wide menu of options, each of them accounting for certain situations. There are flavors for operators that have invested in older technology, and others for those that are starting from scratch. Some are "passive," meaning that there are no electrified components in the field, and others are "active"–and each has its own set of pros and cons.

And sometimes the choice isn't even that easy. In the case of passive optical networks, or PONs, there are three different types of architectures: BPON, EPON and GPON (see sidebar, p. 27).

Despite their use of passive techniques, each type of PON has its own technical distinctions and level of adoption.

BPON got a huge vote in its favor last May when Verizon, BellSouth and SBC Communications pledged to support the technology in a wide-ranging FTTP request for proposal (RFP). Verizon has been the most committal, expecting to pass 1 million BPON-based FTTP homes by year-end and up to 3 million by the end of 2005.

"Verizon's purchases of [BPON equipment] will by itself overshadow what everyone else is doing," says Clifford Holliday, president of B&C Consulting Services. "If the other two (SBC and BellSouth) would actually play the game, that would make it that much more."

Figure 1: Some telcos using BPON plan to offer video via an overlay at 1550 nm.
This illustrates the service assignment of this PON architecture.
Source: Information Gatekeepers.

Verizon's argument, as it is with other telcos that are using the technology, is that the passive nature of BPON will provide a huge savings on plant maintenance because the architecture does not use electronics in the field except at the customer location. Italso leverages the company's massively deployed ATM infrastructure.

SBC plans to use FTTP in greenfield situations and a fiber-to-the-node (FTTN) architecture (serving 300 to 500 homes per node) in legacy areas. BellSouth, meanwhile, offers a much simpler picture. The company has not announced FTTP plans, but continues to use fiber-to-the-curb (FTTC).

Among vendors, Alcatel is presently shipping its 7340 FTTU platform, a derivative of the company's DSLAM product line. SBC is using Alcatel's BPON-based product in Mission Bay, Calif. Alcatel is also gaining traction with municipalities and utility companies, according to Jay Fausch, the company's senior director, strategic marketing.

BPON also holds two key advantages, he explains. For one, it provides a third wavelength of light for video services. Alcatel is working with Scientific-Atlanta to provide an RF video overlay for the BPON platform. Second, it's a stable industry standard that reuses the RBOC ATM infrastructure. BPON's maturity also means that interoperability has been largely completed, and costs have been reduced out of the equipment down to the silicon level, Fausch adds.

But Alcatel also is looking ahead to more advanced FTTP technology.

"There is an evolution in the product path toward a GPON implementation," Fausch says. "The U.S. RBOCs have clearly specified BPON as a near-term direction, but we're seeing other architectures in play in other parts of the world."

While Alcatel decides when to pull the trigger on GPON, other players such as Flexlight Networks and Optical Solutions are already shipping product.

GPON, explains Flexlight President and CEO Gary Lee, will enable operators to support their existing ATM traffic but also handle Ethernet services and a raft of new bandwidth-intensive applications such as IPTV.

Flexlight's GPON implementation supports an ATM-only mode, as well as a mode for generic framing method (GEM), which can carry both Ethernet and TDM traffic.

Flexlight is advocating the GEM mode due to its slim overhead requirements of four to five percent, so usable bandwidth is very high compared to competing platforms that can require overheads of 40 percent, Lee says.

He says a number of service operators are ramping up their activities with Flexlight's GPON platform. Among them, a yet to be named top 10 U.S. MSO is using Flexlight's technology for business service applications. Telcos in Europe and Asia are also in the throes of trials with Flexlight.

But it's hard to say how quickly GPON will reach widespread adoption. "If I were to guess, ultimately the GPON is going to be the technology of choice in the PON world. But the fact that the RBOCs have limited the RFP to BPON really stifles investment in GPON development," Holliday believes.

If BPON is leading the deployment wave, and GPON is the new kid on the block, EPON seems to be the technology sandwiched in the middle.

Because it's Ethernet-based, EPON takes advantage of standard interfaces, explains Bill Dawson, director of technical marketing for access systems at C-COR Inc., which resells an EPON platform from Alloptic Networks under the FTTmaX brand.

Figure 2: Active FTTP architectures like this one from
Amedia Networks are also gaining traction.
Source: Amedia Networks.

EPON has not gained much attention from the U.S. RBOCs. But broadband operators in Asia have been quicker to pick up on EPON technology, notes Mike Serrano, Alloptic's director of product marketing. "They didn't place the IT bets when the U.S. was 10 years ago. They're betting that [EPON] is the next big thing, and they're not going to fall behind."

C-COR has an FTTP deployment with Cable Bahamas, but has not announced anything domestically. But the market is "tremendously active," Dawson adds.

Just because Verizon selected BPON for its initial FTTP rollout doesn't mean that technologies like EPON will be shut out forever, Serrano insists. "Dropping fiber in the ground is one thing; providing service is another," he adds. "I'm not convinced that the RBOCs are truly committed to their ATM infrastructure."

Wave7 Optics, another EPON vendor, often gets confused with a hybrid active/PON provider. That's because it offers the option of a "hardened" optical line termination (OLT) system, which looks like an active component in the field. Other vendors typically put the OLT in a central office and then go passive out to the customer, explains Michael Wearsch, Wave7's vice president of North American Sales.

Like other EPON vendors, Wave7 selected Ethernet for its cost savings.

The Wave7 platform delivers a symmetrical 625 Mbps pipe that is shared among 16 customers. BPON, in comparison, does 622 Mbps down and 155 Mbps up, and divides that among 32 customers.

"You can't predict what will happen in the future, so you have to provide as much [capacity] as you can to the customer," Wearsch says.

Wearsch agrees that the RBOCs can't ignore their legacy infrastructure, but sees BPON as a short-term solution. By way of example, NTT in Japan started with ATM, but is migrating to IP.

One advantage for the EPON, Wearsch points out, is its ability to handle video services over RF or over IP.

Wave7, for example, can install an integrated RF return by changing those packets to IP as they travel along the network. Then, when they reach the headend, the system converts the video back to RF. Wave7's platform is already integrated with Motorola Broadband and Scientific-Atlanta for the RF return, Wearsch says.

If the customer opts for IP video, Wave7's system can provide IP multicasting. But at this point, most (about 85 percent) of Wave7's FTTP customers are offering video via RF rather than IP. But those numbers are certain to change as the cost of doing IP video comes down, Wearsch explains.

Staying active

Like the PON players, makers of "active" FTTP architectures are winning business with smaller telcos, municipalities and utilities. Two high-profile FTTP projects in Utah have opted to take the active route: UTOPIA and iProvo.

UTOPIA, an acronym for The Utah Telecommunication Open Infrastructure Agency, initially plans to serve 11 member cities. Phase I of the UTOPIA project will hook about 50,000 premises in Salt Lake City County to the fiber network over the next year. iProvo, operated by the City of Provo, hopes to build out a network that reaches 27,000 homes and 4,100 businesses in about two years. It is already serving paying customers.

World Wide Packets, which is supplying gear to support the iProvo project, has seen revenue double year-over-year, explains company Vice President Barry Kantner.

Although RBOCs such as Verizon have opted for BPON because of its lower costs, Kantner argues that active architectures have dropped more than 50 percent because the technology uses off-the-shelf Ethernet components. For iProvo, Kantner estimates the equipment (including fiber) and labor to install it costs about $1,500 per every premises passed with a symmetric 100 Mbps connection.

Active architectures better utilize bandwidth for video services, claims Bill Zakowski, vice president of business development at Amedia Networks, an upstart that offers an active FTTP platform through a partnership with Lucent Technologies.

While the BPON crowd is looking to RF broadcast overlays, active platforms send only the channel the subscriber is watching, which can eliminate, or at least prevent, signal theft from rogue set-tops.

"So the content providers feel more secure," Zakowski says. "It's pretty tough to steal [service] if it isn't sent to your home."

He also maintains that the BPON architecture is not completely devoid of plant maintenance. "Even in a passive [environment], the active devices at the customer locations need to be maintained," he says.

Plus, he says, the active approach does not have the same bandwidth limitations of the BPON. In the case of World Wide Packets, its LightningEdge platform can run pipes capable of supplying symmetrical connections of between 100 Mbps to 1 Gbps.

But PON supporters argue that active networks are more expensive to maintain because the components can require environmental controls.

"In the summer, when it gets hot, the actives can become problems," Serrano says.

Although proponents of active FTTP architectures argue that PONs are lacking because they share bandwidth, Wearsch of Wave7 counters that active architectures do indeed share bandwidth via a switch that serves between 12 and 24 customers.

"If they provide 1 Gbps, they don't offer 24 times 1 Gig," he says. "The last few hundred feet [sends] two fibers, but they are sharing that bandwidth into the switch."


The PON triad

BPON: Based on the ITU G.983 standard, BPON uses ATM as a bearer protocol for transmitting in both directions. It originally supported 155 Mbps in both directions, but the latest version supports downstream rates of 622 Mbps and upstream of 155 Mbps. Also known as the APON.

GPON: A new ITU standard (G.984) that carries gigabit rate streams. It is capable of up to 2.5 Gbps in each direction and supports legacy ATM infrastructure.

EPON: Based on the IEEE 802.3 standard for LANs, EPON is Ethernet-based. Not as mature as BPON, EPON developments fall under the auspices of the IEEE. EPON is capable of delivering video over RF or IP.

Sources: Information Gatekeepers, The PON Forum, vendor information