A proxy server and a firewall are devices that filter access
to protected networks. If you are using Net2Phone CommCenter
from work or school, you are most likely behind a firewall.
Your Internet provider could have a firewall set up or could
be using a proxy server. Net2Phone CommCenter can't work through
certain proxy servers or firewalls.
If your provider does have a firewall, it is possible to make
PC2Phone® work through the firewall if you make the necessary
changes. The following FAQs should help you or your network
administrator set up Net2Phone CommCenter® to work behind a
CommCenter uses three ports: two TCP ports and one UDP port.
The first TCP port is used to connect to the messaging server
(relay.net2phone.com:80) for purposes such as log in, maintaining
online status, and instant messaging. CommCenter uses any
available TCP port for this purpose. The second TCP port is
used to connect to a call controller when you make a call.
By default, CommCenter uses any available TCP port for this
purpose as well.
The UDP port is used for voice packets and some control messages.
By default, CommCenter uses UDP port 6801. This port must
be open for both incoming and outgoing data. In other words,
it must be reachable from outside the firewall to allow incoming
packets and the packets sent from it must be allowed to pass
through the firewall. If one of the directions is blocked,
you will have a problem making calls. (The error message "Unable
to contact the calling gateway. (99)" indicates such
a problem.) In some cases, you may also experience one-way
voice, where either you can't hear the person you called or
|Depending on the type of problem you are having,
your network administrator may need to open up certain ports
on the firewall or set up port mapping.|
If you can access Web sites on the Internet without using
a proxy (HTTP or SOCKS proxy), you should be able to log in
to CommCenter without a problem. However, if you can't log in,
ask your network administrator to allow access to relay.net2phone.com:80.
If you use a SOCKS proxy, you can configure the proxy on the
Network tab of the Preferences (via Options menu) dialog. HTTP
proxies are not supported. Since HTTP and certain SOCKS proxies
(SOCKS 4 proxies and some SOCKS 5 proxies) do not support UDP
transport, if you use such a proxy, you will not be able to
make calls -- but you will still be able to login and use the
instant messaging feature of Net2Phone CommCenter.
If the error message "Unable to contact the calling
gateway. (99)"appears, the UDP port is
blocked. Your network administrator needs to open up a UDP
port. By default, CommCenter uses UDP port 6801. If needed,
this port can be changed via a registry entry "UDPPort,"
as shown below in a sample registry file.
If the error message is "We encountered
technical difficulties, please try again later. If you continue
to see this message, and you connect to the Internet through
a firewall, please check with your system administrator to
see if your firewall blocks internet phone calls. (101)",
the second TCP port (as described above) is blocked. Your
network administrator needs to open a TCP port. By default,
CommCenter uses any TCP port that is available. First, you
will need to set the TCP port to a fixed port via a registry
entry "TCPPort," as shown below in a sample registry
If your call connects but you experience one-way voice,
ask your network administrator to set up a UDP port mapping
on the firewall which maps an external UDP port on the firewall
to a UDP port on your machine which is used by Net2Phone CommCenter.
Sample registry file (between the dashed lines):