Mobile Native demo - Communication initiate takes quite a long time before getting video from another end

I tried both android and iPhone, both are slow for the initiation process.
Steps are:
1. start up the node server (start turn/stun server if use local server. I tried both and both have the same issue.)
2. connect to a room name from peer A, the server will say a peer joined
3. connect to the same room from peer B, the sever will say another peer joined the same room
4. click Call from one peer
5. and after about some seconds (more than 10 seconds), both peers have video working

I put this issue here, one reason is that to test with web browsers are working fine. It will be connected the time click Call.

Not sure if this is a known issue. Please advise. Thanks.