Right Bob(s),
Once you inform your ISP, Adelphia in this case, that you now have a new cable modem, they need to know the MAC address (a 12 character number) for it. Once they dial in the MAC into their system, your cable modem will be recognized shortly there after.
I too have Adelphia. I used their cable modem for about a year, when I finally decided to buy my own (a deal that Adelphia was running at the time, I buy a new modem at Circuit City, and I get a hefty rebate).
So, of course, the Adelphia personnel sort of lied to me (so what's new?). They told me that I had to bring in my new modem into their office, so that they can "download required software" into the modem. All lies. All they really needed to do was record the MAC and I could have easily told them that on the phone. But, ok, I take the new modem in, and they write down the MAC. (grrrrrr)
So I get the new modem home and plug it in, and it is working immediately. My download speed was typically 1.5 Mbps. That hadn't changed. However, now I found out that this new cable modem had half the UPload speed of the old one. I complained to Adelphia and they gave me the old song and dance about how different modems have different capabilities, yada, yada, yada. I explained to them that cable modems are capable of up to about 10 Mbps speed, up and down. That I know that with my service, I know I won't be getting anything close to that, and I don't expect that, anyway. But! I do expect something better than the 120 kbps upload that I was now getting. That I was getting about twice that with the old modem. Still, their yada, yada, yada. Grrrrrrr.
Oh well, as they say, they don't guarantee any upload speed, and what I was getting was well within their expected range. Oh well, I don't upload that much anyway.
They're capping the speed, I know their capping the speed, I expect them to cap the speed. At least for as long as I just have residential service. Which is fine for me. I just wish they'd be a little more truthful, and give me back the performance I had with their modem. I had asked for a small window of time for both modems (their old one, my new one) to be enabled at the same time. So that way I could run some speed comparison tests. They told me "can't be done" Another lie. Later I had talked to a support person who said it is done, on occasion, just by allowing both MAC addresses to connect, no big deal. I would just have to pay for service for two connections, but since that would have been just for a day or two, we're talking just a buck or two. Again, no big deal. But, it all depends upon who you talk to. Grrrrr.
Well, a couple weeks later, my upload speed has increased back up to the ~250 kbps speed, and even my download speed has increased a bit, usually I get 2 Mbps and sometimes I see close to 3 Mbps.
Things are rosy again. good luck with your trials of patience with Adelphia. I don't have any serious complaints with Adelphia, just a few little ones. But overall, my service has been good, even great compared to some of my neighbors and their some other company DSL issues.