Nosql database sizing

http://datascale.io/sizing-cassandra-data/

https://www.mongodb.com/blog/post/capacity-planning-and-hardware-provisioning-mongodb-ten-minutes

Traffic Analysis

http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/voip_solutions/TA_ISD.html#wp1015327

Open source telecom solutions

http://www.imszone.org/documentation.html

http://clearwater.readthedocs.io/en/stable/Clearwater_Architecture.html

http://telecom.ashishbanerjee.com/

Jbilling

http://www.simetrictechnology.com/jbilling/jbilling-architecture.html