DOCSIS Cable Modem Guide

Buying a cable modem? Start with DOCSIS.

DOCSIS is the standard that controls how your cable modem talks to your internet provider. The version of DOCSIS your modem uses decides how fast it can go and how “future-proof” it is.

  • DOCSIS 3.0 – older, still fine for many basic plans
  • DOCSIS 3.1 – best all-around choice for most people today
  • DOCSIS 4.0 – next-gen, still rolling out in most areas

Note: your actual speed also depends on your provider, wiring quality, and the plan you pay for.

Jump to the guide ↓
Quick speed idea (theoretical maximums):
3.0: up to ~1 Gbps down 3.1: up to ~10 Gbps down 4.0: up to ~10 Gbps down / 6 Gbps up

You will not see these numbers at home. Your ISP will limit speeds to the plan you’re on.

What is DOCSIS, in simple terms?

DOCSIS stands for Data Over Cable Service Interface Specification. It is just the “rulebook” for how internet data is sent over coaxial cable (the same cable used for TV).

DOCSIS versions – what’s the practical difference?

DOCSIS 2.0 (older)

Mostly legacy gear now
  • Single channel – limited download and upload speeds.
  • Generally not recommended for new purchases.
  • Often not approved for newer speed tiers.

DOCSIS 3.0

Common, but slowly being phased out
  • Uses “channel bonding” to combine multiple channels.
  • Enough for many plans up to around 300–600 Mbps, depending on model.
  • Cheaper, but not very future-proof.

DOCSIS 3.1

Best choice for most home users
  • Designed for gigabit and multi-hundred-meg plans.
  • Better efficiency, often lower latency.
  • Backwards-compatible with DOCSIS 3.0 networks.

DOCSIS 4.0

Newer, still limited availability
  • Aims for much higher upload speeds.
  • Useful if your provider offers very high multi-gig plans.
  • For most people today, still “nice to have”, not required.

Example modem types (by DOCSIS version)

These are category examples so you can see what kind of specs go with each DOCSIS version. Actual models are listed in the “Popular models (2025)” section below.

DOCSIS 3.0 examples

Good for lower-to-mid speed plans
  • 16×4 or 24×8 channel modems – fine for 100–300 Mbps plans.
  • 32×8 channel modems – often used for 300–600 Mbps plans.
  • Best for light streaming, browsing, and casual gaming.

DOCSIS 3.1 examples

Best match for 300 Mbps to 1 Gbps plans
  • Usually marketed as “gigabit cable modem”.
  • Good for multiple 4K streams, work-from-home, online gaming.
  • Most cable companies are moving toward 3.1 as the new standard.

DOCSIS 4.0 examples

Early stage / premium gear
  • Targeted at multi-gigabit download and much faster upload.
  • Requires your provider to actually support DOCSIS 4.0.
  • Overkill if your plan is under 1 Gbps.

Fiber internet: what you need (and why it’s not a “cable modem”)

If your ISP delivers fiber-to-the-home (FTTH), you usually do not buy a DOCSIS modem. Fiber uses an ONT (Optical Network Terminal) — often supplied by the ISP — and then hands you a standard Ethernet port for your router.

Quick picture: 
Fiber line ➜ ONT (“fiber modem”) ➜ Ethernet (WAN) ➜ Your router ➜ Wi‑Fi / switches / devices
Some ISPs combine the ONT + router into one “gateway” box.

1) The ONT (Optical Network Terminal)

The “fiber modem” (usually ISP-provided)
  • Converts the light signal on the fiber into Ethernet.
  • Typically mounted inside (or on an outside wall) with power nearby.
  • You usually rent or receive this from the ISP — buying your own ONT is uncommon unless your ISP explicitly supports it.
  • Common brands you might see from ISPs: Calix, Nokia, Adtran, Alcatel‑Lucent (varies by region/provider).

2) Router / Wi‑Fi (your choice)

What you actually shop for
  • Most fiber installs give you an Ethernet handoff from the ONT into your router’s WAN port.
  • If your ISP provides a combo gateway, ask about bridge mode if you want to use your own router.
  • For larger homes: consider a mesh Wi‑Fi system or multiple wired access points.

3) Speed & ports matter

Especially for 2 Gig / 5 Gig plans
  • For plans up to ~1 Gbps: a standard 1 GbE WAN router is fine.
  • For 2G+ plans: look for 2.5 GbE (or 10 GbE) WAN/LAN ports so you can actually use the speed.
  • Use good cabling: Cat6 is a safe default for multi‑gig inside the building.

4) Ask your ISP these 5 questions

So your setup works on day one
  • Do you provide an ONT or a combo ONT+router gateway?
  • Can I use my own router (and do you support bridge mode)?
  • Does the WAN use DHCP or PPPoE login?
  • Do I need VLAN tagging on the WAN?
  • If I have TV/phone service too, will bypassing the gateway break anything?

Which modem should I actually buy?

You don’t need to chase the biggest possible numbers. Use this as a simple guide:

Important: A faster modem does not automatically give you faster internet. Your provider must offer the speed and configure your modem for that plan.

Quick compatibility checklist