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Re: Cable service and modem compatibility

mjt3727
Tutor

Cable service and modem compatibility

I have interent service with Xfinity supplying up to 300 Mbps download rates. I have a Netgear CM400 modem rated at 340 Mbps. Xfinity claims that this modem is only capable of 150 Mbps. It should be as simple as matching the download rates for both the service and the modem, but Xfinity only recommend modems rated at least at the 600 Mbps level for this service in order to be compatible. What is going on here?

Model: CM400|DOCSIS 3.0 Cable Modem
Message 1 of 7

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djc6
Luminary

Re: Cable service and modem compatibility


@mjt3727 wrote:

Is there a technical reason why ISPs couldn't allow an 8 channel modem on a 300 Mbps subscription?

I don't think there is a technical reason; I just think the provisioning system is setup this way to prevent Comcast reps from doing this.  I'm assuming 99% of people on 300Mbps tier actually want 300Mbps.  This way they don't create situations where customers complain about not receiving advertised speeds.

 

Cox was same way; I was on Ultimate tier (150Mbps) with an 8 channel modem.  At the time, 16 channel modems (or higher) didn't exist.  When Ultimate was bumped to 200Mbps and then to 300Mbps, they wouldn't update my profile for higher speeds until I got a 16+ channel modem.

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Message 7 of 7

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DarrenM
Sr. NETGEAR Moderator

Re: Cable service and modem compatibility

Hello mjt3727

 

It maybe due to the 8 downstream channels Xfinity may need more than that to provide that speed but I would check with comcast again and ask for a explanation on this.

 

DarrenM

Message 2 of 7
djc6
Luminary

Re: Cable service and modem compatibility

DarrenM's assessment is correct.  Cox does the same thing, I couldn't get 300Mbps tier until I upgraded from a modem with 8 downstream channels to one with more.    Here is a nice video produced by Netgear explaining how more downstream channels is beneficial:

 

https://www.youtube.com/watch?v=X4-9ZtThZHs

 

Pickup a Netgear CM600 - on sale at Newegg or Amazon for $90 currently, and its capable of 24 downstream channels - your CM400 can only do eight.  Another option is Netgear CM1000 - it can do 32 downstream channels and is future-proofed for when your area has DOCSIS 3.1 (gigabit) service, but this modem is 2x the price.

 

Just stay away from Netgear CM700 - it has a problematic Intel Puma 6 chipset - do an internet search for "puma 6".  The CM600 and CM1000 use chipsets from Broadcom.

 

Message 3 of 7
mjt3727
Tutor

Re: Cable service and modem compatibility

I appreciate your responses. I only wish the dozen or so tech support agents (tier one and tier 2) I spoke and chatted with from Comcast would have been able to answer this. There are no minimum hardware requirements listed on the Extreme 300 subscription description specifying anything about a minimum number of bonded channels (at the time of writing this). I even spoke with several Netgear support agents who reassured me that this modem was capable of 340 Mbps and should be compatible with the Xfinity service I have. It is unacceptable to me that I have to rely on you fine, knowledgable folks in forums like this in order to get a good answer. What's more, why in the world is 340 Mbps in the product description for this modem if it is only actually compatible with lower tier service? It's extremely misleading marketing that Comcast and Netgear tech support doesn't even seem to understand, and it seems to be an industry standard. Perhaps another modem manufacturer's tech support would have been able to answer this question more quickly (giving the benefit of the doubt), but am I crazy for thinking that a modem with 340 Mbps on the package should, without question, be compatible with a service of 300 Mbps? Consumers shouldn't be responsible for knowing about the technical details of how the rates are achieved with channel bonding - it should be plain and simple. I know I can't be the first person mixed up by this. This is more of a false advertising topic than a tech topic now.

Message 4 of 7
djc6
Luminary

Re: Cable service and modem compatibility


@mjt3727 wrote:

What's more, why in the world is 340 Mbps in the product description for this modem if it is only actually compatible with lower tier service?

Your modem IS capable of 340 Mbps - assuming there isn't heavy use by other customers who share your node. This is because customers are sharing the same downstream/upstream channels. ISPs recommend a 50% buffer (why they want a 600+ Mbps capable modem) so even during times of peak usage (like in the evening) you still get the speeds you are paying for. The speed rating represents the number of downstream channels the modem supports.

 

DOCSIS 3.0 downstream channels are each capable of 42.88 Mbps so if your modem supports 8 downstream channels, thats roughly 340Mbps - assuming your neighbors aren't on the internet at the same time 🙂 More channels means you're more likely to get the speeds you are paying for. Its more important for the higher speed tiers.

 

If you want to see false advertising, check out 32 channel modems or DOCSIS 3.1 modems. For example the Netgear CM1000 claims its capable of speeds of up to 6Gbps! http://www.netgear.com/home/products/networking/cable-modems-routers/CM1000.aspx

 

However, the ethernet port on the modem is capable of max 1Gbps - so why advertise its capable of 6Gbps on the cable interface? You'll never see those speed because the Ethernet port is physically capped at 1Gbps. In this case, the CM1000 is physically incapable of delivering speeds on the box! In your case, the CM400 is at least physically capable of it under theoretical ideal conditions.

Message 5 of 7
mjt3727
Tutor

Re: Cable service and modem compatibility

Hah, well I think they can get away with the CM1000 claims for now since I don't think I've ever even heard of anything close to a 6 Gbps option for any ISP!  

 

Unfortunately it seems that Xfinity not only recommends 600+ Mbps modems for this 300 Mbps service, it seems they require it. They were unable to load the appropriate boot file onto the CM400, so even if I lived in a place where I was the only customer on a node, it doesn't seem like I could use this modem. The support ticket was escalated several times without success (and without response from Xfinity for long periods of time, but that's another story).

 

In my case, I don't need 300 Mbps, but it was actually cheaper than the 75 Mbps package I was previously subscribed to, so I made the switch and bought the least expensive modem I thought should be compatible to save money rather than renting. Even if I was only able to actually achieve 75 to 100 Mbps on a regular basis because of my limited channel number, I'd have been satisfied.

 

Is there a technical reason why ISPs couldn't allow an 8 channel modem on a 300 Mbps subscription? I could see why they would be reluctant because customers would compalin about data rates being below the advertised rates due to channel overcrowding. As I noted though, that's not the case here. I would be a happy camper with lower peak usage speed, since in this case, "lower" is a very relative term. Poor performance on my 300 Mbps subscription would match or outdo tip-top performance on a 75 Mbps subscription.

Message 6 of 7
djc6
Luminary

Re: Cable service and modem compatibility


@mjt3727 wrote:

Is there a technical reason why ISPs couldn't allow an 8 channel modem on a 300 Mbps subscription?

I don't think there is a technical reason; I just think the provisioning system is setup this way to prevent Comcast reps from doing this.  I'm assuming 99% of people on 300Mbps tier actually want 300Mbps.  This way they don't create situations where customers complain about not receiving advertised speeds.

 

Cox was same way; I was on Ultimate tier (150Mbps) with an 8 channel modem.  At the time, 16 channel modems (or higher) didn't exist.  When Ultimate was bumped to 200Mbps and then to 300Mbps, they wouldn't update my profile for higher speeds until I got a 16+ channel modem.

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