There are many different standards and speeds of cable Internet modems and consumers shopping for such a device might have a hard time deciding which one to choose for their own service.
People hear specs like DOCSIS 3.0, DOCSIS 3.1, bonded channels, upload/download throughput etc and usually get confused.
In this article I’ll try to explain and clarify some things about the current cable standards and the speeds that they are capable of so you can make an informed decision if you are shopping for a new cable modem for Internet access.
Let’s start first with discussing the two current DOCSIS standards for cable modem devices.
What is DOCSIS 3.0 cable modem?
DOCSIS stands for Data Over Cable Service Interface Specification. This standard allows for the transfer of data at high-bandwidth over existing cable TV lines.
The standard became popular in many parts of the world because cable TV lines were commonplace, and using them for data transfer means consumers and businesses can benefit from high bandwidth Internet connections without the need to dig up roads to lay fresh telecoms cables.
DOCSIS 3.0 has a maximum upstream speed of 200 Mbps, and a maximum downstream speed of 1 Gbps. It allows for a throughput of 256-QAM, with 42.88 Mbps per 6 MHz channel.
The above speeds are the theoretical maximums. There are many issues that impact the true speeds that a consumer may see, including the connection speed that they pay for, the contention ratio in the area, and also the status of the network that the user has at home.
Moreover, your overall internet speed is affected also by your WiFi signal and coverage in the home. A low quality wifi connection could easily have a lower speed than the theoretical maximum speed of the broadband line.
What is DOCSIS 3.1 cable modem?
This standard is much faster than DOCSIS 3.0, with theoretical maximum speeds of 1 Gbps upstream and 10 Gbps downstream. The maximum throughput is 4096-QAM (1.89 Gbps per 192 Mhz channel).
DOCSIS 3.1 uses Coax cable, which is capable of supporting faster downloads/uploads than ADSL telephone cables used by some Internet providers.
It also offers better security features, a sleep mode to reduce power consumption, and a reduction in packet latency, making it good for VoIP and online gaming.
What are bonded channels in cable modems?
Cable Modems transmit data through channels. Think of a channel as being like a lane on a highway. If there is a lot of traffic on a lane, then it would be considered congested.
A lot of data going back and forth makes the channels your data is traveling along congested too. A traffic jam might make you late for work. A ‘data traffic jam’ might make that video you’re trying to watch start buffering, or the game you’re playing feel laggy.
Modems get around data congestion by having more than one lane, just like busy cities have highways with more than one lane.
To offer the best possible performance, modems use channel bonding to effectively link lanes and improve the performance of the connection.
Bonded channels are written as ‘Number of Downstream channels X Number of Upstream channels’. So, an 8×4 modem would have 8 downstream channels and 4 upstream channels.
Bonded channels are a part of the DOCSIS standard. On paper, each channel on a DOCSIS 3 modem can deliver 38Mbit/s downstream and 27Mbit/s upstream, after any overhead is taken into account.
For example, a 16×4 modem can reach speeds of (16×38 Mbps = 608 Mbps) downlink and (4×27 Mbps = 108 Mbps) uplink throughput.
In the real world, the performance improvement isn’t quite as linear as it seems, and users are unlikely to see the full performance out of their modem.
There are other factors, such as signal to noise ratio, that can impact the speed that a user gets. It is, however, fair to say that the more channels a modem makes use of, the better the performance will be.
Common Modem Bonded Channels and Speeds
The most common configurations seen in DOCSIS 3.0 modems are:
- 4 x 4
- 8 x 4
- 16 x 4
- 24 x 8
- 32 x 8
As more downstream channels are used, it becomes important to also have more upstream channels, in part because when you download files your client software will often have to send acknowledgement packets.
This is far less of an issue now than it used to be in the days of copper telephone lines, however.
The following configurations and speeds are based on the DOCSIS 3.0 standard. Note that EuroDOCSIS is a different standard, with wider 8MHz downstream channels, allowing for higher theoretical speeds.
What is 8×4 Modem?
An 8×4 modem has 8 downstream channels and 4 upstream channels, with theoretical speeds of 304 Mbit/s downstream and 108 Mbit/s upstream.
Users of older 8×4 modems may find their real-world performance of around 50% of the speed that the channels are capable of, due to issues with processor speeds, chipset features, or RAM. Even so, this could be sufficient for someone who is on a lower-tier internet connection.
Usually, an 8×4 cable modem is used by ISPs for speed tiers of around 100Mbps.
What is 16×4 Modem?
A 16×4 modem has 16 downstream channels and 4 upstream channels, with theoretical speeds of 608 Mbit/s downstream and 108 Mbit/s upstream.
Modems with more channels usually have better hardware overall, and speeds of about 60% of the rated performance are likely. This means a 16×4 modem is more than powerful enough for a low or mid-tier internet connection.
Usually, a 16×4 cable modem is used by ISPs for speed tiers of around 300Mbps.
What is 24×8 Modem?
A 24×8 modem has 24 downstream channels and 8 upstream channels, for theoretical speeds of 912 Mbit/s downstream and 216 Mbit/s upstream.
The real-world performance of a 24×8 cable modem is around 60% of its rated speed. This means it should be suitable for ultra-fast cable connections.
Limiting factors for someone who has an ultra-fast cable connection are likely to be slow ethernet (if you’re still using a 10/100 ethernet card, you will not get the full speed), or slow WiFi connection.
What is 32×8 Modem?
A 32×8 modem has 32 downstream channels and 8 upstream channels, for theoretical speeds of 1216 Mbit/s downstream and 216 Mbit/s upstream.
This tier of modem’s maximum performance is around 60% of the theoretical maximum speeds. If a user is not getting that level of performance, it is likely due to slow WiFi, or slow Ethernet. Upgrading to a Gigabit Ethernet card or a better WiFi router may help a lot.
In some cases, slow speeds could actually be due to the maximum speed that the server is capable of providing.
In theory, for example, some older mechanical hard drives may actually read data from the drive more slowly than the cable Internet connection can transmit the data to the user. It’s incredible to think how fast Internet connections have become.
Usually, a 32×8 cable modem is used by ISPs for speed tiers of around 500Mbps.
Gigabit Speed Cable Modems
Although, as shown above, a 32×8 DOCSIS 3.0 cable modem can support gigabit theoretical download speeds, ISPs DO NOT support DOCSIS 3.0 modems for their Gigabit speed tiers.
If you want to subscribe to an actual Gigabit Internet plan with your ISP provider, then you must get a DOCSIS 3.1 modem since only this cable standard is supported for actual Gigabit internet speeds.
Comparison Table of 8×4 vs 16×4 vs 24×8 vs 32×8 Cable Modems
|8×4 Cable Modem||16×4 Cable Modem||24×8 Cable Modem||32×8 Cable Modem|
|Theoretical Downlink/Uplink Speeds||304Mbps / 108Mbps||608Mbps / 108Mbps||912Mbps / 216Mbps||1216Mbps / 216Mbps|
Actual Internet Speed Tier as used in real life
How many downstream channels do I need on my Cable Modem?
As discussed before, each cable modem supports a specific number of downstream and upstream channels, indicated on the modem’s specs as “downstream x upstream”.
For example, a 32×8 DOCSIS cable modem means that it supports 32 Downstream Channels and 8 Upstream Channels.
The higher the number of Downstream channels the higher the Internet download speed supported.
At a minimum, you should choose modems with at least 16 Downstream Channels.
The number of Downstream channels is directly correlated with the ISP speed plan that the modem can support. If you subscribe to a higher Internet speed plan then you might need to buy a modem with more bonded channels.
Here is a brief summary of what Internet Speeds are supported for different Downstream channel modems:
- 16×4 Cable Modem: Can work with ISP plans of up to 300 Mbps
- 24×8 Cable Modem: Can work with ISP plans of up to 400 Mbps
- 32×8 Cable Modem: Can work with ISP plans of up to 500 Mbps
NOTE: You can never go above the Internet speed you are subscribed for. For example, if you pay for a 150Mbps Internet plan from your ISP and you have a 32×8 cable modem, it doesn’t mean that you will be getting 500Mbps.
DOCSIS 3.0 vs 3.1 Cable Modems
The main difference that you need to know between DOCSIS 3.0 and 3.1 modems is that most Internet providers (at least in the USA) require that you have a DOCSIS 3.1 modem for their Gigabit Internet plans (1000 Mbps).
Although in theory a DOCSIS 3.0 modem can support 1 Gbps downstream capacity, in real world internet services this theoretical speed is not achievable.
On the other hand, a DOCSIS 3.1 modem can support 10 Gbps theoretical downstream speed and can easily support 1 Gbps (and even more) of actual Internet speed plans.
DOCSIS 3.1 modems are backwards compatible with DOCSIS 3.0 so if you have the budget we recommend to buy a DOCSIS 3.1 device which uses newer technology and will be future-proof if you ever want to upgrade to a Gigabit Internet plan in the future.
However, most Internet Plans nowadays (i.e ranging between 100-400 Mbps) can be supported by a DOCSIS 3.0 modem.
Should I buy my own cable modem?
Many cable internet providers in the US (and in other parts of the world), such as Spectrum, Comcast, COX, Optimum etc, charge a monthly rental fee to their customers for using the cable modem provided by the service provider.
The modem rental fee can be anywhere between $6-$10 per month, so you are looking at an extra $70 to $120 cost per year.
Most cable modems cost between $60-$120 so by buying your own cable modem you will recover the cost within a year by saving in rental cost. After the first year it will be all savings.
Before buying your own modem though you must check with your current Internet provider to make sure that it will be compatible on their network.
Does a cable modem provide WiFi?
Usually, a cable modem does not provide WiFi so you will need to buy a separate WiFi router for using in your home network.
However, there are “combo” modem/router devices which include a cable modem and WiFi router on the same box. These are more expensive than standalone modems but you will not have to get a separate WiFi router.
Do I need both a modem and a router?
The quick answer is Yes. However, you can have only a cable modem BUT you will be able to connect only a single wired computer (or laptop) to the Internet.
All cable modems come with a single Ethernet LAN port which purpose is to connect it to a WiFi router. The WiFi router will help share the cable Internet connection to all of your home devices (smartphones, laptops, computers, smart-home devices etc).
So although technically you can have only a cable modem, all modern home networks have also a WiFi router together with the modem in order to provide Internet connectivity to the whole home network.
DOCSIS 4.0 Modem
At the time of this writing, there is no DOCSIS 4.0 in the market. Although the DOCSIS 4.0 cable standard has been released recently, modem manufacturers have not yet launched a 4.0 modem in the market (it is a matter of time though).