The BTS (Base Transceiver Station) is responsible for communicating with mobile phones over the network, converting digital signals into radio waves and vice versa. It periodically re-registers the phone's location with the HLR (Home Location Register). The AUC (Authentication Center) contains secret keys in SIM cards used for authentication and ciphering. The BSS (Base Station Subsystem) has two main elements: BTS and BSC (Base Station Controller), which communicates with all BTS through the Abis Interface. The mobile station, also known as a mobile phone or cell phone, has hardware and software components, including the SIM card that identifies the user over the network. The OSS (Operation and Support Subsystem) monitors and controls the GSM network, controlling BSC traffic load. The 2G network offers improved privacy, lower power emission, and introduced many digital services like email and SMS.