Why can’t I have an Audio conversation using MSN Messenger?
For what it’s worth … neither can I. But I know why.
One of the very common devices in use these days is the
broadband router. These boxes allow you to connect one or more
computers to your high speed internet connection. Besides letting more
than one computer share a single connection to the internet, broadband
routers are one of the safest ways to connect because of a technology
called “Network Address Translation” or NAT.
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Using NAT, your computer is effectively “hidden” behind your router.
For example, each computer will be assigned a private IP or network
address that works only behind the router. When that computer then
communicates across the internet that Network Address gets Translated
to a real, publicly visible internet address. It’s safe because from
the internet side of the router there’s no way to initiate contact with
any computers on the private side (unless the router has been
explicitly configured to allow certain types of contact).
Unfortunately that means that some communications protocols which
try to send the address of computer A behind a NAT router over to
computer B somewhere on the internet are destined to fail. They’ll
send the private address computer A has been assigned, which computer
B not being on the private network cannot use.
And so it is with MSN Messenger’s Audio (as well as Video and as I
understand it, file transfer) protocols. They apparently transmit the
IP addresses of both sides of the conversation in ways that NAT routers
don’t know how to translate. So if there’s a NAT anywhere in-between
the conversation can’t happen.
Microsoft Support has a
that gives essentially the same overview, though their discussion is
limitted to Windows 2000 Internet Connection Sharing as the NAT router.
(Step one of their “workaround” is to install a proxy server instead,
which is no small amount of work.) Whether you’re using Windows
internet connection sharing or some other type of NAT router the
concepts and the resulting problem are the same.
So for now those of us behind NAT routers are safe, but at the cost
of not being able to use the audio and video features of Messenger.
It’s my understanding though I’ve not confirmed is that some other
instant messaging products such as
AOL Instant Messenger
(AIM) may use a different protocol and hence may not be affected
by this issue.
You can learn much more about NAT