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I bought 3 modems ( 2 of wich were exctly the same model as the one Comcast has) NONE of them worked... After HOURS and HOURS with their "not so smart" costumer svc agents, they told me they could install it for me for a whoppping $200 service call. I had enough hassles and time waisted so I gave up and continued to pay $7/ mo.

I got the Motorola DOCSIS 3.0 modem to avoid Cox's modem rental. Read the reviews on Amazon and that modem was the best rated i saw. Hooked to my dual band Airport Extreme. My plan is for 15 Mbps, but the modem's multiple stream support gets me a consistent 21Mbps.

I own my Docsis 3 Modem and Airport and use Comcast. I also have an Airport Express which connects to the Modem used with my ViaTalk VOIP. WE have intermittent problems with that phone connection and are considering switching to Comcast VOIP which is supposed to be better. Would I need the Gateway device which messes up Find my Device?

If you have a "business" class account with Comcast (like if your want to avoid the 250GB/mo limit) they won't let you connect your own modem but they will provide a modem without a router.

DOCSIS is also backward compatible. So if you or someone you know has a working DOCSIS 2 siting around, it will work fine.
The only advantage to DOCIS 3 is number of data channels to the cable system, but it is otherwise the same max up and down speed as DOCSIS 2! 42.88 (38) Mbit/s in the U.S., 55.62 (50) Mbit/s in Europe down and 30.72 (27) Mbit/s up everywhere. DOCSIS 3 is the same speeds but on each channel.
Be sure to check with your cable provider to confirm that your plan (or the one you will be getting) on their system will take advantage of additional channels up or down. It is my understanding that most cable providers are still on the one channel system, including Comcast. Meaning that DOCSIS 2 is fine for most people! DOCSIS 1 is the same but upstream is only 10.24 (9) Mbit/s. Again, probably also fine for most of us!

Are you renting that cable modem through a fixed monthly fee? If so, you can insist on a different model, one without a router.

For more serious problems try shouting. A Comcast rep attempting to set up my new DOCSIS 3.0 modem, so badly screwed it up that I lost the Internet both with it and my old cable modem. Call after call got me nowhere. Finally, after about four days offline, I started shouting at the rep to fix my problem, ignoring all her excuses and evasions. They must know what number I was calling from because, from that point on, when I called I got people who actually had the ability to solve my problem. One then put me on a fix-in-24-hours list with a special team. They actually took about 30 hours, but the problem did get fixed and I got refunded for my lost time.

Sorry you were given some incorrect information for that rep. Comcast is pushing the gateways pretty heavy. However, you do not need one to access voice services. What you need is a modem with an eMTA (embedded media transport adapter). We carry and use two models, the Arris TM702 and TM722G, that are DOCSIS3.0 and certified for our Extreme 50 and 105 services. Also, you were given the SMC model gateway, which is not good for Apple products in general. For some reason, SMC does not like to play well with Macs, and we have issues with their routers and gateways when dealing with Macs. Lastly, you CAN save money buying your own modem, whereas eMTAs are pricey. However, if it breaks, you have to eat that cost and buy a new one, if you rent from us then it's replaced at no additional cost. So you have a choice of pay now or pay later.

I had the exact same issue and got the Gateway SMC modem to work. My setup:

Gateway SMC mode connect to Time Capsule (bridge mode off). Time capsule to AEBS by bridge mode. This has worked fine for me. However, as the article states, you need to be somewhat lucky to get a rep that knows how to turn bridge mode off on their end. Also, Comcasts modems coming with 4 ethernet connections, only one can have bridge mode turned off.

sensel, on 23 December 2011 - 12:07 PM, said:

It helps to balance traffic, also.

For DOCSIS 3.0, the Motorola SB6120 is equally good, is said to run cooler, and costs a few dollars less than the SB6121.

DOCSIS 3.0 is required for channel bonding, to achieve speeds up to 2x and 3x faster than DOCSIS 2.0 modems can achieve. If you intend to operate at channel-bonded speeds, be sure you've got a router on the LAN side that can handle the higher-speed throughput. Just being gigabit ethernet isn't enough. Check the actual WAN-LAN throughput specifications of your router.

I had a similar issue of double NAT, and then not being happy with my AirPort Base Station in bridge mode with my AT&T U-Verse gateway. Obviously it's a different system from a cable modem. My solution was to add my AirPort Base Station to the DMZ in the gateway setup. Basically it's outside the firewall, DCHP server and all that. All traffic goes to it by default. I then setup the AirPort Base Station with the standard settings of DCHP and NAT. I get all the benefits of the AirPort's NAT-PMP (or UPnP) and manual port mapping when I need it. I swear it seems resolve DNS faster too. And I didn't have to fool around and try to get my gateway in bridge mode. Perhaps the cable modem has a similar option.

Many years ago when Internet over cable became available in my out of the way location, I signed up with company Y (not Comcast, and doesn't start with Y), and bought a Motorola SB 5100--which had just been released.

The bickering contract couple came and dug in the connection to the house, and a couple of days later the installer came and installed. He couldn't get my modem to work, so we went with the older Moto SB they were renting at the time. Later that afternoon, I got a call from the duty support manager. They had had another 5100 install fail (this one in the Portland area), and reached out to an industry mailing list. They found that they needed to adjust (modernize) a setting in their equipment. The manager and I got my 5100 running in short order, and he arranged for the return of the rental modem.

Since then, company Y has morphed into company X and been acquired in bankruptcy by company W (which hasn't actually happened yet). And my 5100 died of old age (as the 5100 seems quite willing to do). With my current (Linksys) modem and a bankrupt provider, my service is more reliable than it ever was.

Meanwhile, neighbors moved in to the newly-built house next door and called Comcast (and satellite companies). Comcast quoted a $2,500 installation fee--rather interesting in that they have no franchise rights in this county (they do serve the next county over). Neighbors went with satellite before I pointed out that they should call company X if they wanted cable.

--John

I had to go this route too. But I immediately purchased the cable modem as opposed to getting entangled with Comcast and there cryptic hardware. I have not had any problem what so ever and swapping the hardware was easy as calling Comcast and informing them of my new equipment. Everything took less than 20 minutes.