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Is it possible that after establishing a SIP phone call my conversation partner is able to identify my location? If so what are the prerequisites and how accurate would he be to do so?

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SIP separates call signaling and voice data, to allow SIP routers to remove themselves from the data path. Some software does this, some doesn't, so whether the remote party is given your IP address depends on the SIP routers on the way.

In the easy case where your SIP client is running on a machine with a global IP address, it will open a random local port for voice traffic, and send an INVITE packet containing the global IP and the port number, which is forwarded verbatim to the client on the other side, which then uses it to establish a connection. This method works even if the other side is behind NAT, and routes actual voice traffic in the most direct way possible, but both sides of the conversation learn the IP address of the remote party.

If both sides are behind NAT, software may attempt to configure NAT traversal, if it succeeds, we're back to the first case.

If NAT traversal doesn't work and a proxy is available, or a router on the path is configured to route all traffic through a proxy, it will modify the address given in the INVITE message, do the same in the reply, and both sides will only learn the IP address of the proxy.

IP addresses are not accurate locations, but allow some educated guesses. IP geolocation is its own topic, so I've focused on the SIP specific aspects here.

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