As a company we provided SIP based telephony solutions. We've previously used Draytek routers, but would prefer to switch all our customers to Mikrotik routers, due to their superior performance and configurability.
We've already done so at various sites, including our own, and with correct port forwarding, IP PBXs such as 3CX work fine behind the NAT setup of the router, for both SP Trunk connections and for remote handset connections to it.
However, when I replace the Draytek or BT router at a remote site, the handset(s) there still register, but only get one way media for all calls. Specifically they only send media, but will not receive it. The remote handsets (usually Yealink T22's) are configured to work behind NAT firewalls and use STUN. For all other makes of router, this has just worked without any special setup. STUN should in theory overcome the NAT problems of the secondary media stream on the different ports for the original SIP signalling, but it doesn't seem to with Mikrotik routers at the remote sites.
I have read through the forums and tried with SIP NAT Helper on and off, but it makes not difference. Can anyone tell me exactly what this helper does and why we are having these issues. Is the Mikrotik implementation of NAT a Symmetric NAT or something else?
Andrew Kent-Brown MTCNA
Aspen Technologies Ltd