RE: [Sipping] Making SBCs more transparent for NAT traversal

[Juha Heinanen <jh at tutpro.com>]

Markus.Isomaki at nokia.com writes:

 > If we assume that the wireless access provider indeed uses NAT, and
 > is not able/willing to do any specific configurations for them, ...

markus,

since in mobile networks, NAT is most likely implemented in GGSN or
somewhere close to it, that NAT (since it is service provide controlled)
should be mobile network friendly by default and keep NAT bindings open
when receiving keepalives from the proxy.  

it could also be clever and not pass these keepalives to the mobile
terminal, thus saving battery power.  this works ok if there is no other
nat behind a mobile terminal, for example, when SIP application sits in
the mobile terminal itself.

so mobile operators, if they ever want to be SIP friendly (which may not
be the case) could have a separate access point name for mobile
terminals that actually terminate the traffic (as in the example above)
and a separate access point name for cases where there is a network
behind the mobile terminal.

in the latter case, keepalives would not be absorbed by the mobile
operator NAT, but that would be ok, because the mobile terminal that has
a network behind it most likely will have constant power available and
thus the power problem doesn't exist.

markus, you are free to pass this on to your product development
department :-).

-- juha

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