Phone.com Setup and Troubleshooting Guide
Cisco SPA122 Analog Telephone Adapter (ATA) with Router
8 / 9
Revised: 30 October 2012
If you have a router where this feature cannot be disabled:
●
Consider putting your VoIP device in the router’s DMZ. (Consult the user guide for your
router for specific guidance.) Though this will expose that device to the internet, it
eliminates the SIP ALG issue for it, while still using your existing network hardware. Most
consumer routers can only assign one IP address to the DMZ.
●
Consider purchasing a router where disabling this feature is possible. This way your VoIP
device can remain behind the protection of the router’s firewall.
●
You can choose to connect your SPA122 to your modem, then connect your router to the
SPA122, so that the device is no longer inside your router’s network. See the “This all
sounds too complicated” section below for more.
Make sure your network is not “double-NAT”ted.
Network Address Translation (NAT) is what a router does to get traffic to your computer. “Double-
NAT” is an issue where two routers are placed one after another. This can be a common issue if,
for example, someone adds a router to a network that already has a modem/router combination
device.
A computer that is behind a double-NAT setup can usually still browse the web, while other
activities like sending and receiving email might be problematic. More advanced applications—like
VoIP—are not likely to work at all.
To resolve this issue, you will need to put the modem/router device into “bridged” mode. Most
modem/router combination devices will allow this. This will disable all routing and NAT functions on
the modem/router, so only the standalone router will perform these functions.
DSL modem/routers may support “half-bridged” mode, where the modem will take care of the login
authentication but leaves the NAT functions to the standalone router. If “half-bridged” mode is not
possible, select “bridged” mode instead, and input the login authentication details into the
standalone router. Contact your internet service provider if you need specific guidance.
This all sounds too complicated. Is there an easier way?
If changing these settings sounds like it is more than you want to get into, or if your router will not let you
change some of these settings, you can use your SPA122 ATA as a router instead of your normal one.
See
Figure C
below.
Your normal router will not interfere with VoIP calls.
Your ATA will limit your internet upload/download speeds (~20 Mbps).
You may have to configure your ATA to connect to your ISP.
