Standards Watch : Making Sense of Passive Optical Networks

With APON here, and a GPON there, EPON, BPON, everywhere a PON PON. This sounds like a lyrical nursery rhyme until you try to make sense of it. Regardless of the flavor of PON, it seems that passive optical networks will play an important role in the deployment of voice, video and data service bundles (see “The Race to Bundle Voice, Data and Video,” p. 20). PON is sparking interest as carriers begin to realize that fiber costs no more than coax or hybrid fiber coax (HFC) networks to deploy and offers far superior performance with less operational headaches.

Fiber-based access networks traditionally utilized SONET’s add-drop multiplexers, which can be exorbitantly expensive, given the process of locating a venue to drop them and then laying concrete. Whenever technology advances or bandwidth upgrades are needed, electronics have to be changed out and new hardware purchased.

On the other hand, PONs offer higher bandwidth without truck rolls, forklifts and upgrades, as they leverage an embedded base of fiber. For mid-size and small businesses with embedded fiber bases, PON might be a cost-effective alternative to point-to-point or ring-based networks. PON could become an alternative to point-to-point fiber solutions, especially in residential areas, where one wavelength could be used for data services and another for broadcast TV services.

In other words, once additional bandwidth is required—and users get into the 155 Mbps to 200 Mbps range—customers can possibly be assigned their own wavelengths, as PON enables companies to selectively upgrade customers on an as-needed basis—upgrading only the parts of the network that are affected, rather than the entire network. Additionally, PONs work regardless of the protocols running over them.

PON Alphabet Soup

When numerous carriers worked on the FSAN (full service access network) standard with the ITU, APON developed under ITUg.983. The IEEE also was active with vendors and some carriers developing EPON under the auspices of its First Mile Alliance. Also under development is GPON (gigabit PON).

When fiber to the business was the trend in the late ‘90s, the industry was fragmented among Ethernet PON (EPON) and ATM PON (APON) proponents, as well as hard Ethernet switches. Initially, carriers were taking a wait-and-see approach, as no one knew if EPON or APON would prevail.

But, ILECs, with money to burn, invested heavily in ATM, making APON the one to gain momentum first. APON then became pervasively known as broadband PON (BPON).

“The broadband PON architecture introduced three wavelengths of light—meaning carriers could dedicate one to video and offer cable TV services that were superior to those over traditional networks,” says Mark Klimek, senior director of business development for Alcatel, which is working with SBC and a few other RBOCs on fiber-to-the-premises buildouts. SBC is deploying Alcatel’s 7340 FTTU (Fiber to the User) system, which consists of several PON-based elements, including equipment for the central office and business and home terminals.

The gauntlet was dropped last year, as a triumvirate of RBOCs announced that they would standardize on BPON. Verizon, BellSouth and SBC announced that they would invest in optical components and integrated circuits based on BPON.

“If RBOCs succeed with BPON, it will drive volume and innovation, thus bringing the cost down significantly,” says Jeff Wynne, senior vice president of marketing for Motorola (formerly Quantum Bridge, recently acquired by Motorola). Quantum worked jointly with Motorola to develop fiber to the home (FTTH) devices for cable modems and set-top boxes.

Despite its momentum and maturity, EPON is emerging as a lower-cost alternative for some municipalities and companies targeting small business and multi-dwelling residential areas.

For them, EPON provides high bandwidth on behalf of multiple service providers on a wholesale basis to both homes and businesses. “There are lots of Ethernet switches out there, which is cheaper,” says Wynne, adding that there are still many that do not use Ethernet components. That means APON’s maturity still could trump EPON in terms of mass adoption down the road. While EPON is gaining traction in Asia, especially China, where Motorola has a big presence, it still faces challenges—the most noticeable of which is to handle the upstream traffic, moving away from the traditional, collision-based Ethernet protocol, says Wynne.

In the end, carriers won’t care what letter is in front of PON.