Thomas M. re: <According to that article, cable is faster than DSL.>
Cable can be a lot faster than DSL. The key point is that cable performance is impacted by the number of users simultaneously accessing it. Cable has limited bandwidth available to the subscribers, and if a lot of users are on, performance starts to degrade. Think of it as a LAN. There are numerous contention and sharing issues that aren't experienced by DSL. That's why the study showed performance deterioration during peak hours. Here's a copy of a PM I sent someone in February. It explains my concerns about cable.
I was thinking more about it last night.
My rather simplistic view of the local phone switch vs, local cable.
Seem's that the cumulative bandwidth of the wire into the switch is higher than that available from cable. While each subscriber is limited to around 50kbs on modem, (higher if they can use DSL), that's pretty much available regardless of how many are connected.
My local cable provider, Media General, has 230,000 subscribers and has the capacity for 120 channels, of which about 100 are currently dedicated. Assuming that 20 channels of bandwidth are available for internet services, I'm guessing that's about 120mHz. (They're bringing "RoadRunner" up in the near future, but I have no idea how much bandwidth will be dedicated to that service).
But even if it's all used for RoadRunner, the amount available to an individual subscriber would seem to be inversely proportional to the number of users actively on-line.
So if they provide a desirable service, ie: movie download, it would seem to be a serious problem if many subscribers want to avail themselves of that service.
Even if only 1,000 users are trying to download simultaneously, that's just 120kHz per user. Take a heck of a long time to download.
And what if another 1,000 are on the net trying to view streaming real-time video?
They have a caveat in their info for potential subscribers.
"The speed at which Road Runner will deliver Web sites and other Internet content to your computer will vary, depending on the Web sites you access, the amount of congestion on the Internet, the speed of your computer, and the number of people in your neighborhood who are also downloading information at that instant. However, compared to the alternatives, Road Runner wins hands down".
While I have no doubt it will "win hands down" in the early stages, is this really the solution that will provide a "TV channel per user" in the next century?
My guess is there will need to be major changes in local cable infrastructure if they are to meet the hype. Probably a community broadband fibre backbone with "star" like connecting point drops located throughout the neighborhood.
These changes will be a long time in coming. The interim experience could sour a lot of users on cable.
I think it's a lot easier for the Bells to add DSL connections to their switches than it is for cable to resolve the contention/sharing issues.
BTW, the biggest problem I see with DSL is the need for close proximity to the switch.
JMO's of course.
Gene |
