Router/Firewall Configuration

Many routers will work 'out of the box' for VoIP but some may need changes to work optimally.

There are two issues which may concern your router;

  • Call Quality
  • Phone Blocking

Aside: We recommend using a dd-wrt flashed router as it works well for VoIP and is highly configurable. It also provides useful tools for managing your local network. Dd-wrt is free and works with many common routers. If your existing router does not have support for features such as QoS, check if it can be re-flashed with dd-wrt.

Call Quality

The quality of your calls should be better than a regular phone (when using HD codecs). If you have poor quality calls it may be your router is not configured for QoS (Quality of Service). QoS ensures VoIP is allocated a higher priority than data. This is especially important when there are a number of users on the local network (youtube downloads need to share the network with your phone!).

If you have limited Internet Bandwidth the quality of the connection may also degrade when usage is close to maximum. QoS settings can also regulate the Internet Bandwidth preventing it from becoming overloaded.

When considering connecting with VoIP we recommend you check your router has support for QoS. If your router does not have QoS we would recommend you install a router which does.

There are different ways technically to configure QoS on a network. How it works will depend on your router features. The simplest way is using the phones MAC address (hardware address). Essentially this means any data from the phone is high priority. Refer to your router manual to check how QoS should be configured.

This is what settings for QoS look like on a dd-wrt router.

Internet connection bandwidth limits for a 3Mb/300kb connection
Phone MAC addresses are set to Premium

Phone Blocking

When signalling passes through your router they will go through a firewall and a NAT (Network Address Translation). In some cases there may also be a component called and ALG (Application Level Gateway). These can all cause 'blocking', the symptoms of this are;

  • VoIP phone unable to REGISTER (go online).
  • VoIP phone does not ring when called.
  • One way audio or no audio.

In many cases these can be solved by changing the router settings, in some cases a router replacement is best.

If you have any of the symptoms above, this is a list of things you can try;

  • Disable any SIP ALG your router has.
  • Test with your firwall off and gradually increase security settings on the router (don't leave your firewall off).
  • Place the IP phone in a DMZ on your router.
  • Forward the local SIP port to your phone (default will be UDP 5060).
  • Forward the local RTP ports to your phone (check your phone for UDP range settings).

Using VoIP Topics