The Home Location Register (HLR) is a database that contains details of each SIM card subscriber that is authorized to use a particular GSM network. The HLR is maintained by the network operator. Each SIM has a unique identifier called an International Mobile Subscriber Identity (IMSI) which is the primary key to each HLR record.

Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts the packets of data sent over an internet protocol network. It is used in Virtual Private Networks (VPNs).

Internet Protocol security (IPsec) uses cryptographic security services to protect communications over Internet Protocol (IP) networks. IPsec supports network-level peer authentication, data-origin authentication, data integrity, data confidentiality (encryption), and replay protection.