[Live-devel] HOW REALIZED NAT TRAVERSAL IN LIVE555

[Ross Finlayson]

> How Live555 client side library makes UDP ports reachable from the global network for incoming UDP traffic when both client and server are under NAT

In short, it can't.  RTSP works by having a RTSP client contact a RTSP server, to request a specific stream.  If the RTSP client can't contact the RTSP server, either by name or IP address (because the server is behind a NAT and has only a private IP address), then RTSP won't work.  (On the other hand, if just the RTSP client - but not the RTSP server - is hidden behind a NAT, then RTSP will often work OK.)

What people usually do to overcome this is put a "LIVE555 Proxy Server" on a public-facing computer (i.e., one that has a public IP address), and have that proxy server stream from a 'back-end' RTSP server that can be on a private network.  (If the proxy server computer can't contact the 'back-end' server, then instead, the 'back-end' server can contact the proxy server, using our custom RTSP "REGISTER" command, as described in our proxy server documentation: <http://www.live555.com/proxyServer/>)  Then, clients (including those that are themselves behind a NAT) can access the stream via the (public) proxy server.


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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