Broadband Speed Wars Part 3: Verizon and FTTP
by Leslie Ellis // November 28 2005
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 first, which favors augmenting its DSL (digital subscriber line) techniques.
This time, we look into the theoretical speed max for Verizon, with its fiber-to-the-premises (FTTP) 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:
“By the way, the 25 Mbps bogey on VDSL2 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 high definition TV. 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 Gigabits-per-second (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.)
Broadband Maxes in Review
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 (Very High Bit Rate Digital Subscriber Line) 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 550-750 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 550-750 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 DOCSIS 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.
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.
This column originally appeared in the Broadband Week section of Multichannel News.
Broadband Max Calculations Part 2: SBC & VDSL
by Leslie Ellis // November 06 2005
If there’s one thing that’s wild about telephone companies, it’s how much their technology strategies differ, one to the next.
SBC Communications, for instance, is taking a path that combines a little bit more fiber with a lot more work on its DSL (digital subscriber line) techniques. Verizon plans to go long with fiber, and barely bother with DSL.
SBC: The 25 Mbps Max
This week’s translation will focus on the theoretical and practical broadband max speeds for SBC, which detailed its technology progress to analysts in New York on Nov. 3 (and posted the information to its web site; search on “IPTV.”)
During the briefing, SBC plainly stated its max speed: “Using VDSL in conjunction with gigabit Ethernet technology, bandwidth of 20-25 Mbps was achieved, sufficient to provide four streams of high quality video (including one HD stream) per line, high-speed Internet access, and, in the future, consumer VoIP service.”
But it never hurts to go beyond the obvious. “VDSL,” for starters, stands for “Very High Bit Rate Digital Subscriber Line.” VDSL is one technology in the offspring of ADSL (Asymmetrical DSL), or what consumers know as just plain DSL.
VDSL is different because it’s faster (duh). It’s faster, in part, because it reaches higher up the wire, spectrally, than “regular” DSL. Specifically, it runs up as high as 30 MHz — versus the 1.1 MHz range of today’s DSL. Rule of thumb #1: The higher the frequency, the harder stuff is to manage, technically.
Then, there’s the matter of “loop length,” or the actual footage of the twisted-pair phone wires that loop from your house to the central office or neighborhood node. Rule of thumb #2: The longer the loop, the slower the speeds, for all flavors of DSL.
(A reference point: People who study loop lengths say that 12,000 feet is the most prevalent in the U.S. — about half of us live in houses with that footage.)
SBC plans to shorten its copper loops, to 3,000 feet, for 18 million homes within its footprint. Deadline: June of ’08. Decreasing loop lengths means increasing fiber lengths — in SBC’s case, to neighborhood nodes of 300-500 homes.
The relationship between VDSL and loop length is an intimate one. On short loops, with low service penetration, VDSL sings. On long loops, piled with services and customers, it wimpers. This explains the plan to get to a 3,000-foot loop length as quickly as possible. (It doesn’t explain why only a portion of SBC’s footprint gets the fiber booster.)
There are other variables that impact DSL speeds, not mentioned in the SBC update, but closely watched by bandwidth aficionados. One is the number of copper pairs in the wire bundle connecting homes to a central office.
Rule of thumb #3: The more twisted pairs there are in a wire bundle, the more potential there is for “cross-talk,” which happens when signals leak out and crash into each other. This is especially true of digital services, riding in that higher spectral zone.
That’s some of the behind-the-release details about SBC’s broadband plans. That 25 Mbps speed downstream, using VDSL and deeper fiber, is their deployable broadband max. VDSL can go higher, theoretically — up to 100 Mbps, the vendor community says — but that’s with very short loops, and pristine conditions.
Short of stretching fiber all the way to homes (which SBC plans for new housing areas), SBC’s deployable broadband max will likely remain 25 Mbps, downstream.
Next time, how to do the math on broadband max speeds for fiber-to-the-home networks, like Verizon’s “FiOS.”
This column originally appeared in the Broadband Week section of Multichannel News.