Today, Comcast announced a new modem that’s been tested to a blazingly fast 150 megabit/sec, which is significantly faster than anything else on the market today. This is great news for video-hungry home users and others who have a need for speed; current products can only support up to 50 megabits/sec. The new product conforms to the DOCSIS (Data Over Cable Service Interface Specification) 3.0 standard, which can be viewed in more detail at Cable Labs’ web site. To give some perspective to this accomplishment, the demonstrators “downloaded the 32-volume Encyclopaedia Britannica 2007 and Merriam-Webster’s visual dictionary in under four minutes, when it would have taken a standard modem three hours and 12 minutes.” They also said the same operation over a dial-up modem would have taken weeks (at the old 56k standard).

Speed is key; I recall the days of text-only 300 baud (bits per second) telephone modems and having the ability to read the text faster than it could be scrolled to the screen. The faster the modem, the more information you can send and receive in a given period of time without bogging down your system. But before everyone gets too excited and queues up to buy one of the new devices, which won’t be commercially available for some time, we all need to remember that the local cable speed is only one component in the overall cable experience, just as the telephone system’s local loop is only one part of a DSL connection. In order, the string of devices and transport media involved in a network request includes the PC’s internal subsystems, its built in network card (often rated at 100 megabit/sec), the cable or DSL device, the cabling system to the local office or distribution point, the trunk line to the provider’s main Internet Core connection, the Core connections themselves, and the network/system at the receiving end.

In order for the new systems to achieve their full potential, each and every link in the chain would need to be rated at, and configured for, 150 megabit/sec communications. Fiber’s capacity is theoretically unlimited, but intervening devices such as routers, switches, and other active components are often limited to much lower bandwidth, based on the service provider and other factors. Just as the chain is only as strong as its weakest link, the speed of a given connection is constrained by its slowest component. If you’re streaming video from Company X’s server, and that company’s network connection is only 10MBPS, then that’s all you’ll get. Even if the connection is 150MBPS, system load and network traffic levels will affect the final rate. If the server is busily serving hundreds of simultaneous data streams, its own internal limitations (e.g. disk or system bus speeds, CPU capacity, and memory size) could make that data stream run much more slowly than the network’s capacity.
Obviously, this advance should stimulate another round of upgrades by ISPs and companies that serve content on a large-scale basis. It’ll be interesting to see where we are in terms of network capacity and speed by 2017!