Complete beginner here, but having problems! I use VOIP on a laptop with a USB phone and '3CX for Windows' on the hapLITE - no issues. I have the CSIPSimple app on my Android phone. This works fine on my home network (Billion router) BUT on the hapLITE network, while I can dial and hear the number ringing, there is no return audio from the dialled number. A lot of Googling suggests there may be a problem with 'SIPALG'?

If anyone has any suggestions, please keep them simple!

Details
CSIP SimpleVersion 1.02.03r2457
ISP Zoom Internet (UK)
VOIP Provider Sipgate UK

I have asked both ISP and VOIP provider for help, and am awaiting a response.

On Mikrotik, go ip->firewall->service-port, set the "sip" row to "disabled" to switch off the SIP ALG functionality, reboot the Mikrotik, wait for it to come back, try CSIP Simple again.

Thank you Sindy. Will not be in that area for a few days but have printed your post off and will advise.

The advice is based on my years old experience that if something was not perfect in a SIP message, the ALG in RouterOS was unable to recognize it as being a SIP message and did not forward it at all (the message was coming from the exchange side in my case, and the exchange vendor has fixed this particular already; in your case it seems that it is something about CSIP Simple given that another softphone running on Windows experiences no issues, or so I've understood from your post at least). Other vendors' SIP ALGs used to have their own issues.

Another experience says that as a VoIP provider, you cannot rely on SIP ALG to exist and work properly at each client side. So most VoIP providers' exchanges deal with NAT at client end by means of ignoring the RTP socket address indicated in clients' SDPs, learning from what socket the RTP from the client actually comes to the socket on a public IP which they have indicated in their own SDP, and sending the RTP for the client to that learned socket. This approach has some drawbacks too, but in general it has a much higher success rate than depending on clients to have a working SIP ALG which also plays along with their CPEs. So it should be safe to switch the SIP ALG off at Mikrotik.

Yes - that sorted it - thanks.