Following on from my initial post this is a very short post to describe my network and telephony topology.

I’m in the very privileged class who own their own class-C network from way-back. The assholes at AUNIC keep on trying to steal it back by ever more draconian rules to make it impossible for me to keep my in-addr-arpa domain alive. Luckily I have survived so far but my design plan allows for transition to a NAT model if required.

At present I have an upstream SIP Trunk provider who runs Asterisk (Pthuewee!). I have some PSTN numbers that they rout to my Kamailio instance that I then distribute to my extensions. My extensions are registered to my Kamailio server. I also run rtpproxy so that external extensions can have a proxy IP address for media within the permitted range for my SIP trunk provider..

My internal numbering system has extensions in the 200 range. This works a lot better than 100 series which are continually probed by exploit bots.

I have entries in db_aliases that match PSTN numbers to specific 200 series extensions. In reverse I can translate internal extensions to PSTN numbers in the outgoing headers.

All works fine except when I want to do a call transfer between extensions. My upstream Asterisk provider doesn’t support REFER messages. Even worse it sends fake progress messages as though it does support them but actually does nothing. This is the main reason I have decided to set up a Kamailio/SEMS PBX where I can take control of the trunk system and also provide more functionality within my network and remote extensions.

Ultimately SEMS will (probably) replace rtpproxy and the upstream provider will have zero control of my PBX and DID/DDI numbers.



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