Options abound for boosting cable upstream speeds
The return path lags behind downstream speed, but cable is working on its game plan.
In a shot across the cable industry’s bow, Verizon rolled out a revamped data lineup that included significant speed upgrades on the return path earlier this summer.
To go with its 300 Mbps downstream speed, Verizon is now offering an upstream speed of 65 Mbps in addition to 150/65, 75/35 and 50/25 tiers. By contrast, North American cable operators are paced by Videotron’s 200/35 service that launched earlier this year in Quebec. Comcast’s highest return path speed can burst up to 20 Mbps, while Cablevision clocks in with 15 Mbps on the upstream.
For now, Verizon has the bragging rights on both the fastest downstream and upstream speeds in North America. Should cable operators be concerned? It depends on whom you ask, but there are options on the table for increasing the upstream speeds in both the short term and long term.
“We were certainly pushing hard on this a few years ago, and frankly there wasn’t a lot of interest, but in the last three to six months, the amount of interest has risen dramatically on upstream bandwidth,” said Jeff Walker, director of CMTS product marketing for Motorola Mobility. “Interest has really risen with Verizon announcing its new offerings.”
Walker said there were several drivers for increasing the speed on the return path: subscribers are starting to synchronize their content in cloud-based central depositories; the gap between downstream speed and upstream speed needs to be closed; to keep pace with the competition; and to support some of the new devices and services, such as video conferencing, that are starting to put a strain on the return path.
Buckeye CableSystem CTO Joe Jensen said customers aren’t demanding faster upstream speeds, but his company is working on increasing them. Buckeye launched a wideband tier with a download speed of 110 Mbps, with 5 Mbps on the upstream, earlier this year.
“Well from our perspective, we’re OK, but we do need to plan for additional upstream as the needs of our customers move us in that direction,” Jensen said. “We kind of see this war going on; sometimes the downstream speeds are the hot topic, and other times it turns around where we see more growth on the upstream.”
Videotron’s Pierre Roy, vice president of engineering, research and development, said his company has kept a finger on the pulse of its subscribers by first launching a 120 Mbps down, 20 Mbps up tier in 2010, and then this year’s Ultimate-Speed Internet 200.
“What I see from the numbers is people are very content with what they have,” Roy said. “Some customers want it, but a lot of them do not need major upstream speeds. I would say what they really need is downstream speed and capacity.”
While there doesn’t seem to be a widespread movement underfoot to increase speeds on the return path, Comcast has achieved speeds of 75 Mbps on the upstream by bonding four channels during lab and field trials. Cox Communications and Motorola hit 400 Mbps on a 5-85 MHz return path last year at an industry event.
With basic video subscribers diminishing, data services are becoming more of a cash cow for cable operators, and the cable industry is ready to deal from its upstream deck once the demand is there.
The present: Bond more channels, split those nodes
John Chapman, CTO of Cisco’s Cable Access Business Unit, said the majority of cable operators that are deploying DOCSIS 3.0 services today are bonding four channels on the upstream and three on cable modems on the 5 MHz to 42 MHz return path.
“I would say that we still have headroom on the existing upstream,” Chapman said. “If you look at the cable modem technology we have today, we have eight channels down, four channels up. The game now is really how much bandwidth can you get out of four channels? Most operators aren’t even deploying four channels yet, or they are deploying four channels, but they’re not doing it at full modulation.
“The tricky part is when does that headroom run out? How often does Verizon put out these new speeds? As a cable industry, we have to be planning what our next move is going to be in three to five years. I think in zero to three years we have headroom, and we’re in good shape, but we’re always looking ahead to see what’s next and where we can go.”
Roy said DOCSIS 3.0 still has a long shelf life and that Videotron could split nodes and bond more channels in the near term to increase upstream and downstream speeds.
Jensen said that Buckeye CableSystem could nominally support 20 Mbps on the upstream, but work is underway to boost that to 90 Mbps before summer is over.
“We’re working on putting together plans to expand our upstreams to be able to get three 6.4s upstream with 16 QAM, hopefully moving to 64 QAM across the board,” he said. “That would give you roughly 90 megabits upstream per segment, and I think it would certainly offer us the ability to move upwards in that upstream data rate category, but it’s all a management issue.”
Buckeye had to replace the older Fabry-Perot lasers in the field and clear up spectrum space to increase the upstream speeds.
“We had to move some of our signaling activities so that we could clear that out, but that’s moving forward, and I’m anticipating over the next 30 days (sometime in August) we’ll have that done,” Jensen said. “Then we’re going to selectively turn up nodes as we see the need, because once we get the spectrum cleared, then we need to make sure we have DFB (distributed feedback) laser replacements for the Fabry-Perot lasers, and then we can light that additional bandwidth up.
“We’ll watch the upstream, we’ll manage the network very carefully, and as we see growth in certain segments, we’ll go in and fix them. We’ll reach a point where we’ll just turn on the rest of it and clean up the rest of the nodes, but right now it’s on a kind of as-needed basis.”
DOCSIS 3.0 also supports mid splits in the 85 MHz range, although so far, other than Massillon Cable having its plant ready for 85 MHz, there hasn’t been much action.
“If you had Verizon show up with 100 megabits or 200 megabits in the upstream, then with the technology that exists in DOCSIS 3.0, we could go bump the spectrum up to 85 MHz and drop in eight carriers,” Cisco’s Chapman said. “Eight carriers at about 25 megabits per second per carrier is a 200 megabit effective return path. So we could offer a shared 200-megabit-per-second return path, and on a per-subscriber basis, you might be comfortable provisioning maybe 100 megabits or something on the return path for a subscriber.
“So the technology we’re shipping today could be used as is, and with minor plant changes, you could easily get the upstream to 100 megabits per second and the downstream to a gigabit.”
As for high splits and top splits, Motorola’s Walker said the jury is still out, but “everything is still on the table” as CableLabs and cable operators size up their options.
Motorola finds traction with S-CDMA
Motorola has been touting the benefits of Synchronous Code Division Multiple Access (S-CDMA) for years now as a solution for making the noisy 5 MHz to 15 MHz range suitable for things such as upstream channel bonding. According to Walker, there are cable operators testing S-CDMA, including several in North America.
S-CDMA is supported in DOCSIS 2.0, but Walker said the 3.0 version does a better job of reducing ingress noise and helps improve modulation capabilities.
“With DOCSIS 3.0, we’ve proven the ability to actually achieve 256 QAM in the return path using DOCSIS 3.0 S-CDMA,” he said. “So essentially, that ability to use the three additional channels below 20 MHz is going to give you 50 to 60 more megabits per second, which is perhaps 45 percent or 50 percent in your return path bandwidth by using that S-CDMA capability.
“In order to do six channels, you really need to be able to use that spectrum from 5 MHz to 20 MHz, which traditionally has not been possible because of the combined impulse and ingress noise, but S-CDMA addresses that. We’re seeing tremendous interest in S-CDMA now.”
New chipsets in the offing
Upstream speeds can also receive a boost from new silicon chipsets. Intel’s Puma 6 DOCSIS 3.0 chip has 24-channel capabilities, while Broadcom is reportedly working on a 32-channel wideband chip.
According to Motorola’s Tom Dunleavy, senior director of marketing and product management, those next-generation platforms will start to be available next year. Cable operators may not need that sort of capability in the upstream right away, but having them in place does future-proof customer premises equipment. Dunleavy said in most cases, the new silicon chips would be used in triple-play gateway devices as cable operators migrate to video over IP.
The next generation of DOCSIS
At this year’s Cable Show in Boston, there was discussion about the next iteration of DOCSIS, which was being referred to as DOCSIS NG and DOCSIS 3.1. Among other features, Chapman said that DOCSIS NG could include a new forward error correction (FEC) with LDPC (low density parity check) codes that would provide higher modulation capabilities. Orthogonal frequency division multiplexing (OFDM) would also add noise mitigation features and “is very attractive from an implementation point of view,” according to Chapman.
“We’ll get a bump in bit capacity by going with some newer technology in the upstream,” Chapman said.
Cable could also increase its upstream speed via Ethernet PON over Coax (EPoC), or with a combination of DOCSIS and EPoC.
Chapman has a map for how the upstream will evolve. Over the course of the next three years, cable operators’ plans will center on deployments that use the full 8 x 4 cable modems and the 85 MHz mid split that is available now if they want to go to eight channels in the upstream. The next step would center on how to implement the new 24 x 8 or 32 x 8 chipsets.
“Now beyond that in the longer-term horizon, the questions come along like, ‘Could we do a gigabit in the upstream some day?’” Chapman said. “Our research that we’re doing right now says we think we could push the cable plant to a gigabit plus in the upstream. So we’re looking at technologies to do that, and it does involve plant splits to get those types of rates. We’re looking at more advanced modulations to get those rates.
“What we’re finding is that we have a very nice choice of technologies available for us, and it looks really feasible to do. The next step really is to sit down and consolidate on some choices and then go figure out a way to do it.”
Meanwhile, on the downstream …
Verizon’s claim to having the fastest downstream speed was short-lived.
On July 24, Comcast announced that it would start offering a 305 Mbps down, 65 Mbps up service, which it calls Xfinity Platinum Internet, throughout markets in its Northeast Division. The residential service, which costs $300 a month, uses fiber to achieve the fastest download speed in the U.S.
Comcast is also providing a dedicated “Personal Communications Consultant” for each subscriber to Xfinity Platinum Internet. The consultant will work one-on-one with each subscriber to ensure that the service elements, which include a wireless gateway for home networking, function correctly.
In June, Verizon trotted out its FiOS Quantum tiers, which feature the 300 Mbps down, 65 Mbps up tier, as well as three other offerings: 150/65, 75/35 and 50/25.
Prior to Verizon’s Quantum launches, Canadian cable operator Videotron had the fastest speed by a large ISP in North America with its DOCSIS 3.0-based 200/35 tier. Comcast’s fastest wideband tier to date features 105 Mbps on the downstream. Other notable speeds in North America include Suddenlink’s 107/5, Comcast’s 105/10, Cablevision’s 101/15 and Charter’s 100/5.
DOCSIS 3.0 has plenty of headroom for cable operators to hit 300 Mbps on the downstream with eight channels available for bonding, which would give them a theoretical speed of 320 Mbps.
Currently, the bulk of cable operators that are offering DOCSIS 3.0 wideband tiers are bonding four channels down and three up.
Videotron’s Pierre Roy, vice president of engineering, research and development, said his company is bonding seven or eight channels on the downstream for its Ultimate-Speed Internet 200 tier.
Doing node splits and adding more channels gives cable operators plenty of legroom to match or exceed Verizon’s fiber-based offerings, without the addition of the GPON and EPON equipment that Verizon’s top two tiers require.
On the silicon front, Intel’s Puma 6 DOCSIS 3.0 chip supports 24 channels, while Broadcom is reportedly working on a 32-channel chipset, both of which would enable downstream speeds of 1 Gbps. New silicon could be available next year.
The speed wars between cable operators and Verizon are really about bragging rights, as most residential subscribers probably aren’t willing to fork out $209.99 a month for Verizon’s fastest tier. Comcast has the deep pockets and a team of engineers to strategically deploy a 305 tier in select Verizon markets, but the majority of cable operators will sit in the grandstands during the speed wars until there’s a big enough demand by subscribers to warrant the investment.
In March, Buckeye CableSystem rolled out a 110 Mbps down, 5 Mbps tier that at the time was second only to Videotron’s 120 Mbps tier. Buckeye is bonding four channels on the downstream to hit 110 Mbps, according to CTO Joe Jensen.
“We’ve seen very soft takeup on our 110 down, 5 up product,” Jensen said recently. “It’s a lot of market sizzle. It’s gratifying that we can demonstrate that kind of capability on our network. As far as we can tell, there’s a core group of customers that want the fastest speed and are willing to pay for it, but for the most part, a large segment of customers are happy with the current speeds we provide that are lower than 110.”