Hello! I have kamailio 5.5 configured with digest authentication.
DB Mysql, 2 rtpengine one on the same server with kamailio, the other is separate.
Rtpengins work in bridge mode, internal/external/external-ipV6.
Kamailio listen 3 address: internal/external/external-ipV6 work in mixed mode: ipV4-ipV4, ipV4-ipV6, ipV6-ipV6.
OS Debian 10, CPU 1 core, Ram 4gb, Disk not ssd.
internal address is used for the gateway model of the connection to the PSTN. Before sending a call to PSTN, a request is sent to Billing by Diameter (request over the network, ims_charging ), Billing responds in the region of 10-17 milliseconds. usrloc db_mode = 0; UAS contacts are received according to the PUSH scheme (we send PUSH via http and get a REGISTER). children = 8 for each;
When running synthetic tests with sipp, I get 36 cps as a maximum, but there are a lot of retrans.
This is a test environment.

  Product:
I plan to get 100 cps; 20k concurrent calls, hardware will be 128GB RAM ddr4-2400; Intel Xeon Silver 4216, Optane SSD. 2 such servers, kamailio/rtpengine are configured exactly according to the scheme of the test environment.

Question:
Can you please tell me how many children, shm/pv do I need?
Is it worth going in the direction of asynchrony, or is the standard one enough for my purpose?
I will be very glad for any help.
Thank you!