Why HSS is used in LTE instead of HLR?

Question

I have a query that why HLR is not used in LTE Network instead HSS is used. I know that HLR doesn't support diameter protocol but only SS7's MAP where as HSS supports diameter protocol. Is there any other reasons related to data type or authentication type ?

Thanks Piyush

Solution

The Home Subscribe Server is the main IMS database which also acts as database in EPC. The HSS is a super HLR that combined legacy HLR and AuC functions together for CS and PS domains. In the IMS architecture, the HSS connects to application servers as well as the Call Session Control Function (CSCF) using the DIAMETER protocol.

In other words :

The HSS (Home Subscriber Server) is the concatenation of the HLR (Home Location Register) and the AuC (Authentication Center) – two functions being already present in pre-IMS 2G/GSM and 3G/UMTS networks.

The HLR part of the HSS is in charge of storing and updating when necessary the database containing all the user subscription information, including (list is non exhaustive):

· User identification and addressing – this corresponds to the IMSI (International Mobile Subscriber Identity) and MSISDN (Mobile Subscriber ISDN Number) or mobile telephone number.

· User profile information – this includes service subscription states and user-subscribed Quality of Service information (such as maximum allowed bit rate or allowed traffic class).

The AuC part of the HSS is in charge of generating security information from user identity keys. This security information is provided to the HLR and further communicated to other entities in the network. Security information is mainly used for:

· Mutual network-terminal authentication.

· Radio path ciphering and integrity protection, to ensure data and signalling transmitted between the network and the terminal is neither eavesdropped nor altered.