Update: Videotron bonding 4 channels on upstream with 64 QAM
Bonding channels on the upstream is part of the feature set of DOCSIS 3.0, but to date North American cable operators have been slow to pull the trigger on deployments with the exception of Videotron.
Videotron's Ultimate Speed Internet 120, which launched in Quebec City, features speeds of up to 120 Mbps on the downstream and 20 Mbps on the upstream. As noted yesterday , the downstream speed is the fastest by a cable operator in North American, while the 20 Mbps on the upstream also looks like the top speed by a cable operator in an actual deployment. (Verizon has a 50 Mbps down, 20 Mbps up tier and has tested a 100 Mbps downstream tier.)
To get the 20 Mbps on the upstream, Videotron is bonding four channels in conjunction with 64 QAM modulation. (Midcontinent Communications was an early adopter of 64 QAM with Cisco several years ago.)
While Comcast has been testing upstream channel bonding and upgrading to 64 QAM, Videotron's launch yesterday may have marked the first deployment of upstream channel bonding in North America by a major cable operator. Videotron was also the first cable operator in North America to launch a DOCSIS 3.0-based service two years ago.
Worldwide, Japan Cablenet deployed upstream channel bonding  with Arris last year.
With the rush to deploy DOCSIS 3.0 services with faster downstream speeds, especially in areas where there is increased telco competition, upstream channel bonding has been the red-haired stepchild to date, but cable operators could start increasing their upstream speeds by the end of this year or early next year.
While the capability to bond upstream channels is in place, vendors and cable operator employees that I've spoken to in the past have said there hasn't been much of a demand for faster speeds on the return path. But faster upstream speeds will be appealing to small and medium-sized businesses that need to send large files back and forth between offices.
For a good run down on the challenges of upstream channel bonding, check out this recent Open Mic column by Wim Mostert, director of product management for Optical Transport Solutions at Aurora Networks .
As for vendors for Ultimate Speed Internet 120, Videotron is using Motorola's 6180 cable modem and Cisco's uBR10012 cable modem termination system (CMTS).