Hello We are implementing an architecture with Kamailio and Asterisk with real time and are debating who should be the Registrar for the SIP clients. We are biased towards leaving that to Kamailio and use Asterisk to provide the media services: vmail, conference etc. It looks like this is the recommended way as per several tutorials on the net suggest that solution. As a down side we will have to use a combination of near-end [STUN, ALG] and far-end Nat solutions [rtp-proxy] to handle the media and also are kind of worried about how we should handle the Cass 5 features tipical of a residential line. But a member of our team suggests to use Asterisk for that and have Kamailio forwarding the REGISTER request from the clients to the Asterisk. Asterisk can handle media and also users behind a NAT. We have never done it that way and we are not sure whether it is possible or not, whether it is acceptable SIP-wise or not. For example: if the proxy is load balancing the REGISTER messages then the clients should be given the IP of the proxy to send the REGISTERs and the NAT binding in the customer's NAT/Firewall will be associated to the IP of the proxy, not the IP of the Asterisk. On then other hand, Asterisk as a PBX supports a lot of Class 5 features natively. We would like to hear your input, suggestions and comments about this, what other people are doing. If we had only a few user then 1 Asterisk box should be enough but we are planning on having way more that what an Asterisk machine alone can handle, that is why we want to load balance using kamailio. regards jp