Verizon Spells Out 100 Mbit/s
That's not to say 100 Mbit/s, even a bit diluted, is child's play. Verizon has come forward as the only major U.S. carrier to say that delivering 100 Mbit/s to the individual home is on its radar. (See Verizon Leads the Great 100-Mbit/s Bandwidth Race.) It's just that getting there won't be easy.
Luckily, Verizon won't have to saturate its network with 100-Mbit/s lines. "At any stage we don't have 32 people looking for 100-Mbit/s service," says Vincent O'Byrne, director of access technologies at Verizon. "We would do some oversubscription."
That means Verizon is betting that whenever 100 Mbit/s first becomes a reality, the demand will be minimal. "It's not likely that everyone would want it," says O'Byrne. "It would be a small percentage of people in any neighborhood."
Good thing, too. Verizon says that most of its central offices serve about 15,000 to 20,000 homes. Simple math would dictate that to bring 100 Mbit/s to each of those homes would require at least 1.5 Tbit/s of bandwidth going into each central office. That of course is not how things work now.
While Verizon's migration from BPON to GPON will play a big role in the movement towards 100 Mbit/s, traffic management will be just as significant.
"When you oversubscribe, you have aggregators behind the OLT [optical line terminal] which take advantage of the dead space of the transmission from one OLT to another," says O'Byrne. "It is taking advantage of statistical multiplexing and the fact that not everyone is accessing that 100 Mbit/s at the same time."
In the long run, Verizon is considering the possibility of upgrading its network with Wavelength Division Multiplexing (WDM), or WDM-PON. This technology sends a full wavelength to each house, greatly increasing the potential capacity of each fiber.
"We're making sure that when we deploy our GPONs, that we have the capability when there is a need, to increase our network's output. Part of our overall strategy is to make sure our network can evolve to WDM," says O'Byrne.
For now though, O'Byrne says that Verizon is expecting GPON to have a long lifespan that won't get cut short by WDM-PON.
"There are different substantiations of WDM," O'Byrne says. "There are some variants that allow you to evolve off the present GPON, and they sort of become another GPON channel."
But even with network capacity upgrades, oversubscription, and multiplexing, signing up for 100-Mbit/s service won't mean you'll get that bandwidth all the time. "100 Mbit/s isn't guaranteed," O'Byrne says. "If you ran a test on the network, it would read 100 Mbit/s, but if enough people were demanding it at the same time, we couldn't guarantee each would get the 100 Mbit/s."
— Raymond McConville, Reporter, Light Reading