[OpenSIPS-Users] packet forwarding when two mediaproxy 2.0s are back-to-back

Juha Heinanen jh at tutpro.com
Thu Sep 4 16:55:30 CEST 2008

one user behind nat and mediaproxy 2.0 claims that when he makes a call
to another user also behind another nat and another mediaproxy 2.0, each
mediaproxy keeps on waiting packets from the other one and as result
nothing happens:

ua1 - mediaproxy1 - mediaproxy2 -ua2

so from mediaproxy1's point of view, ua2 is not behind nat and vice
verse, because both mediaproxies have public media addresses.

should this text from mediaproxy 1.9 README be still valid for
mediaproxy 2.0 or has something changed?

  After it has allocated the sockets for each stream, the proxy will listen for
  an incoming packet from the 2 parties. Once these arrive, the proxy is able
  to know where the packets should be forwarded and can start forwarding them
  between the 2 parties. Please note however that if one party is not behind
  NAT the proxy server is able to send packets to it even before it receives a
  packet from it, since the IP/port is already known. Because of this, our
  mediaproxy server is able to work even when chained with another mediaproxy
  server. There will be no blocking of the media streams because both mediaproxy
  servers are passive and wait forever for a packet from each other. Instead our
  mediaproxy server will only be passive and wait for a packet if the party it
  talks with is behind NAT making it possible to chain as many mediaproxy
  servers without blocking.

i haven't yet had possibility to personally verify the claimed behavior.

-- juha

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