Manual

Issue #2 is more complex, but there are some workarounds:
1 The simplest way of avoiding NAT issues is not to use NAT at all. If your router supports a DMZ
function, this will have the effect of putting your client (EarShot IFB) open to all incoming traffic on
the Internet. Alternately, EarShot IFB can be located directly on an open Internet connection with a
fixed, public IP programmed into it.
2 Many modern routers and firewalls have a feature called SIP ALG that may be either on or off
by default. If SIP ALG is designed correctly (and not all implementations are), your router will
be smart enough to “sniff” the command SIP channel, predict where incoming RTP streams are
expected, and route them to the proper ports on your SIP device. The one magic rule of SIP ALG
use is to avoid the use of other workarounds simultaneously - SIP ALG assumes it’s the only one
tasked with NAT traversal and will malfunction if other workarounds are employed.
3 Use a SIP provider that has implemented their own complete NAT solution. Several providers have
systems that have been finely tuned to resolve the NAT issue for RTP streams. They can detect the
difference between public and private addressing, and proxy all the media data between the
clients if necessary, making NAT traversal much simpler. You can inquire whether your SIP provider
implements a “NAT solution” and in particular whether they employ a “media relay”, which means
the provider can act as a proxy for your calls.
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