Xfinity/Comcast uses various cable modems to connect their customers to their internet services. They do allow their customers to purchase their own equipment.

Good/Preferred Modems:

 - Netgear CM500

 - Netgear CM600

 - Netgear CM1000

 - Arris SURFBoard SB8200

Bad Modems:

 - Netgear CM700

 - Motorola

 - Arris SURFBoard (Except the SB8200)

 - Cisco (DPC Series)

 - SMC

 - TP-Link

 - Zoom

Required Settings:

 - Disable IPv6

 - Disable entire Firewall

 - Disable SIP ALG

I have a "bad" modem, what can I do?

Comcast/Xfinity allows you to purchase and bring your own modem. Purchase a Netgear CM500 (or above), and when you're ready to install it, give them a call. They will require some information about the modem before you can plug it in.

What makes a "bad" modem?

The bad modems listed above will introduce noise into your phone calls. They are very old modems that contain processors that can't handle the load of multiple phone calls happening at the same time. They introduce things like jitter and packet loss into the connection.

Even though these modems might work well for the normal internet connection (email, Facebook, etc.) they are not sufficient for a very sensitive system like VoIP.