Installation with a DSL Connection
DSL connections can be more challenging since most DSL modems are also routers and supply DHCP. Some even have firewalls and will do SPI state-full packet inspection. This can cause double NAT issues, one-way audio and other connectivity problems.
When installing for the first time you may want to follow these steps:
. With an Ethernet cable connecting the ATA (Analog Telephone Adapter)
directly to the DSL modem, and a phone connected into the first phone port, power up the ATA. Check for dial tone, after waiting for a minute or two. If you have dial tone then check for two-way audio. If you have two way audio, then:
. Connect the router to the DSL modem, using the router as a switch (disabling DHCP).
. If you do not get a dial tone, or have one-way audio then, you will need to make the DSL modem a bridge and set the router to connect using PPPoE. This will require the correct username (in the correct format) and password for your DSL account.
After configuring the DSL modem to a bridge the next step will be to configure the router/IAD to use PPPoE as it's connection type.
Installation in a Business Networked Environment.
Installation in more complicated networks may require special configurations, depending on the actual network. One of the most important correctable issues would be to check for double NAT.
A few ideas to overcome installation problems are:
. Connect the ATA directly to the first device and check for two-way audio. If you get one-way audio or no dial tone, then the issue will most likely be SIP unfriendly NAT, or a firewall that is not allowing the needed packets to cross.
. Try port forwarding or IP tunneling; send the needed packets directly to the ATA. These will usually be UDP ports 5060, 5061 and a range of higher UDP ports. You will need to get the exact ports from VoiceLift.
. Place the ATA in a DMZ or perimeter zone, or
. Place the ATA outside any firewall and NAT, allowing it to receive a public IP address.
Remember that different NAT transversals and firewalls can play havoc with SIP.
The issue occurs due the nature of the VoIP protocols. The signaling of the device is handled by one protocol, but the voice is handled by another protocol. The voice protocol may not be associated with the device, so the router does not know where to send that information. The result can be one-way audio.