For years, the Internet's technical constraints went hand-in-hand with the realities of Internet usage.
At first, most people viewed Web pages but did little to create or change them. Web journals, photo sites and video sharing didn't come until later. Even when users had a need to send information — an e-mail here, a shopping transaction there — the amount of data was small.
High-speed Internet services that offered relatively slow speeds for sending, or uploading, data served most consumers fine.
But as those consumers evolve into contributors and require better upload speeds, many of the old technical constraints remain.
Consider DSL services from phone companies.
The souped-up phone lines were originally developed for video on demand. Most of the traffic goes from the service provider to the home. Users only need to send occasional commands to buy and start shows.
So engineers felt justified in designing a system that largely sent traffic in one direction.
In doing so, they were able to limit interference between the two signals — one for each direction — sharing the line, said John Cioffi, a Stanford engineering professor and pioneer in DSL technology. It would have been possible to give both signals equal treatment, he said, but that would have reduced the line's overall capacity.
Think of it as two people next to each other, both shouting while trying to listen to something from a distant location. "All you can hear is your neighbor," Cioffi said.
"If your neighbor is only allowed to shout very infrequently, then most of the time you can listen," he said.
In other words, limit traffic from the home to the central office so that everyone can get good download speeds.
Similar limits exist for cable, though for different technical reasons.
Decades ago, the Federal Communications Commission assigned broadcasters a range of frequencies, starting with 54 megahertz for Channel 2. Cable operators had to squeeze upstream data into the space below, said John Mattson, a senior marketing director for Cisco Systems Inc.'s cable products.
Although nothing required upstream allocations to be contiguous, splitting the channels would have added cost, John Chapman, a distinguished engineer with Cisco's cable unit.
"Every time you change directions, you have to add additional (equipment) to accommodate," he said.
Satellite Internet services, meanwhile, have their own constraints. Some systems send data in one direction only, meaning you'd need a regular — and slow — phone line for uploading.
Techniques are being developed to address some of the uploading constraints.
Cioffi said newer flavors of DSL can eliminate the signal interference, similar to how noise-cancellation headsets can intercept unwanted sounds and transmit their opposites to cancel each other. But he said the technique will require phone companies to install new equipment at central offices — and that equipment isn't commercially available yet.
Likewise, cable companies can upgrade their systems to boost upload capacity. Over the past few years, they have gradually been deploying modems and other equipment using a system called DOCSIS 2.0, which transmits data more efficiently, doubling the capacity within the existing frequencies, Chapman and Mattson said.
DOCSIS 3.0 was recently approved, allowing service providers to use a wider range of frequencies. Once the equipment becomes available, upstream bandwidth can increase right away — and even more if the FCC releases the analog spectrum after broadcasters fully move to digital in a few years.
"We have a good technical road map for the next five to 10 years," Chapman said. "It's all a matter now of economics."
By Anick Jesdanun