Timothy, if you simply do the math, you will see that there is no bandwidth problem as the result of the shared medium.
Cox has built to 1000 homes passed. I have been told that they intend to upgrade to 500 homes passed at some point in the future.
What "1000 homes passed" means, is that there is a "node" for each 1000 homes that the cable "passes". The 1000 does not represent subscribers, but simply homes, which may or may not contain cable customers or @Home subscribers.
Let's assume that Cox keeps good on their promise to build to 500 homes passed, and also assume a VERY optimistic penetration of 50%. The same numbers would apply at 1000 homes passed with 25% penetration. 25% penetration would have @Home investors dancing in the streets.
500 homes x 50% penetration = 250 subscribers/node.
Let's assume 50% usage during the peak hour. I think that this number is high, but perhaps not TOO high. (Probably closer to 25%.)
Downstream bandwidth is 26Mbit/sec. Because downstream is unidirectional, there are no collisions as on Ethernet, so we can count on the full 26Mbit/sec being usable. (There is no doubt some protocol overhead which should be subtracted, but I will ignore this for purposes of this discussion.)
(Each user can only get a maximum of 10Mbit/sec, due to the Ethernet card speed, but the speed on the cable is 26Mbit/sec).
Now, let's make one more terribly unrealistic assumption - that all of the users on during the peak hour will be downloading, full-bore, continuously.
What do you think? Gonna be pitiful, right?
OK, we've got 125 peak users (500 homes x 50% penetration x 50% usage at peak) sharing 26Mbit/sec. 26Mbit / 125 = 208,000 kbit/sec, or about double 2B ISDN.
As a practical matter, users will probably see many times this speed at peak, because my number for penetration is probably overly-optimistic, and my numbers for the # of users at peak and the user load (e.g. 1.0) are overly-pessimistic.
If people are just doing typical web browsing (not downloading the latest 100MB mega-killer game) their load on the system is going to be insignificant. (e.g. 10% load would probably be on the high side for web browsing, so now at peak you are looking at 2Mbit/sec. Better than having a dedicated T-1.)
Me, I'm still squeezing even more unbelievable speed out of this thing through upgrades to my PC. First was an upgrade to a hot PCI Ethernet card. Then, an upgrade from Windows 95 to Windows NT. (NT does TCP/IP networking MUCH faster than 95, and the difference is QUITE noticible when you are using a cable modem.) |
