Child realm membership

Hi,

I'm designing an access realm with registration for multiple customers. I want to use 1 shared IP for all customers, but also want some level of granular control per customer. For example the ability to set different media management per customer.

The best way to do this seems to be to create a parent realm (with sip-if) and child realms for each customer. The child realms can then have customer specific settings.

My question is which is the best way to assign membership to child realms? It seems I have a few options, from assigning different sip-if IP addresses or ports, to specifying customer IP addresses/networks. Neither of these options seem great to me, so I was wondering if something can be done with the SIP messages and HMR? Something along the lines of a HMR to check the SIP message for a customer specific information (From header maybe?) and set a trunk group header which can then be used to assign the child realm?