CSG-Id-List  IE ( 128 )

Closed Subscribers Group (CSG) identifies a group of subscribers who are permitted to access one or more CSG Cells of the PLMN. To make CSG Call, UE should send CSG ID to which it belongs and it's access type in Attach Request. MME then performs UE Authentication with the HSS and then exchangs Update location Request and Answer. In update location location answer, HSS sends CSG info (CSG ID, Subscription Timer) in subscription Data.

Reference: TS 36.413-f10   View