What is meant by NASS bundled authentication scheme, gprs ims bundled authentication scheme, sip digest auth scheme?

Question

What is meant by NASS bundled authentication scheme, GPRS IMS bundled authentication scheme,sip digest authentication scheme and what is the difference between them and on what conditions the are chosen?

Answer 1

All of them are used for IMS authentication, In early days when IMS was being deployed full flexed security system was not in place.
Earlier IMS system was relying on different authentication procedure to consider an UE authenticated. In NASS-IMS bundled authentication, IMS considers UE as authenticated based on network authentication.
In case of GPRS-IMS bundled authentication (GIBA), IMS sub system relies on GPRS authentication. There is no separate IMS authentication procedure is required.
SIP digest authentication scheme is the one which comes under the IMS authentication.

Comments

Does this mean that all the three authentication schemes will be present for a single IMS authentication (NASS bundled IMS authentication,GPRS bundled ims authentication,sip digest authentication)