The last two translations examined theoretical maximums for downstream broadband speeds — first for cable, then for telcos. Because the telcos are taking radically different approaches, we examined SBC Communications Inc. first, which favors augmenting its digital-subscriber-line techniques.
This time, we look into the theoretical speed max for Verizon Communications Inc., with its fiber-to-the-premise plans.
But first, a quick dip into the mail, if only to illustrate what often happens when stating the known differences between competing techniques: Stuff changes; new facts emerge. Here’s a comment from a writer friend, who covers the telcos, about the Nov. 6 SBC column:
LOOP-LENGTH FACTOR
“By the way, the 25 Mbps bogey on VDSL2 [very high bit rate DSL] is geared to a max loop length of 5,000 feet. At 3,000 feet, they get 40 Mbps.”
He went on to say that SBC is also thinking of “bonding pairs” (aggregating the throughput of two phone lines) to serve higher demand for HDTV. Making that move would nudge SBC to a theoretical max of 50 Mbps at a 5,000-foot loop length, and 80 Mbps at a 3,000-foot loop length, he said.
But back to Verizon, which appears to be nearing its target of 3 million homes passed with FTTP by the end of next month.
In some ways, Verizon’s “FiOS” plans are cable-ish. Many of the optical techniques (and suppliers) used by the cable industry are in use by Verizon to send multichannel video (including analog) and digital services (broadband Internet, voice) to homes.
It’s one thing to run something past a home. It’s another to connect a home. For Verizon to talk in terms of passings, it means they’re not taking glass to the side of the house, until someone asks for it. Makes sense.
Verizon’s plans include the use of optical splitters, to send signals over that last piece of glass running from the telephone pole or pedestal, to the side of the house. This matters to its theoretical broadband max, because the plan is to split a downstream signal 24 times. With each split, the theoretical max slims.
Before the optical splitter, there is, admittedly, a broadband gusher: Around 622 Mbps of downstream capacity, divided amongst the two dozen homes. Upstream, a beefy 155 Mbps.
INTRODUCING THE 'PONS’
Technically, those speeds are dictated by Verizon’s choice of network protocol. Verizon wants to use a technique known as “B-PON,” for “Broadband-Passive Optical Network.”
Note that there are ample prefixes for the telco acronym “PON,” which is spoken like the word “pawn.” As a sampler, there’s B-PON (Broadband). E-PON (Ethernet). G-PON (Gigabit). Moo Goo Gai PON (kidding.)
Both Verizon and SBC are expected to move toward G-PON, which affords 2.5 Gbps, in both directions — toward homes, and away from homes. But that isn’t likely to happen until the supplier community responds in a bigger way, PON aficionados say.
The “passive” in “passive optical network” means electricity isn’t required to light signals from one place to another, over glass. So it’s passive as in “no power needed,” not passive as in “yes, dear.”
The various PON prefixes describe the protocol used to send digital information over the network. (Recall that a “protocol” is set of rules that define how two or more pieces of equipment “talk” to each other.)
MAXIMUM SPEEDS: A RECAP
Here’s a quick summary of this three-part series on theoretical broadband maxes: SBC is gearing up to hit a 40 Mbps downstream max, using VDSL over loop lengths of 3,000 feet. If they need more, they’ll consider “bonding pairs,” to clump the throughput of two phone lines.
Verizon wants to leapfrog its installed base of copper-pair phone wires, moving instead to an all-fiber network that jets 622 Mbps of downstream capacity to a splitter serving around two dozen homes.
The math for cable goes like this: As many digital channels (spectrally located between 550 MHz and 750 MHz) as can be cleared off for broadband, times 38 Mbps, which is the speed afforded by 256 QAM (quadrature amplitude modulation).
If that “digital shelf space” between 550 MHz and 750 MHz was completely empty, for instance, cable’s theoretical broadband max would sit somewhere around 1.2 Gbps (200 MHz, divided by 6 MHz channel width, times 38 Mbps).
Doing it would require Data Over Cable Service Interface Specification 3.0 to bond those 33 channels, and sum the throughput.
That’s double Verizon’s 622 Mbps. It’s also an unlikely scenario, at least until cable providers can start reclaiming their analog spectrum for digital use. Making orphans of digital channels, video on demand, voice and HDTV doesn’t seem like a good plan.
CHANNEL BONDING ON WAY
Right now, most operators dedicate one, maybe two 6 MHz channels to broadband Internet connections. A conservative estimate points to 2007 as the time when standardized equipment will be available (based on DOCSIS 3.0) to let them bond channels, and sum the throughput.
I’ll close with this, from the Department of the Obvious: As theoretical max speeds go, the showdown will be between cable and Verizon.
Verizon’s plans require gobs of money, and tight execution.
Cable’s plans require cross-industry unity, intense bandwidth management, and vigilant marketing.
Translation: It’s not time to curl up into the fetal position just yet.
Stumped by gibberish? Visit Leslie Ellis at www.translation-please.com.
