Opensips has mid-registrar module. It's a method of forwarding registration data to another registrar (usually with a much higher expiration). The idea is to handle high volumes of registrations at opensips and only forward the registration data to another registrar when the data changes. 
Kamailio doesn't have a mid-registrar module, and IMO, for good reason. The concept of a mid-registrar doesn't make a lot of sense to me as there are much better ways to scale registration data without forwarding REGISTER packets to other registrars.

On Thu, Dec 17, 2020, 7:41 PM Alex Balashov <abalashov@evaristesys.com> wrote:
It would probably help if you could state exactly what it is that you
are trying to achieve. The term "mid-registrar" encompasses a fairly
large category of conceivable configurations, though all of them have in
common, I suppose, the quality of not passing through registrations
upstream in a 1:1 fashion.

On 12/17/20 9:38 PM, moisesynfante wrote:
> Hello,
>
> I'm a newbie when it comes to Kamailio and I would like to know if there's a
> working example of a Mid-Registrar implementation. I read on other posts
> that the UAC module can be used to achieve this but, honestly, I don't
> understand how. If any of you could provide some path I could follow I would
> be very thankful.
>
>
>
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