S-TMSI (S-temporary mobile subscriber identity)
S-TMSI, which stands for S-Temporary Mobile Subscriber Identity, is an identifier used in cellular networks to uniquely identify a mobile subscriber. It is a temporary identity assigned to a subscriber by the network operator, and its primary purpose is to enhance subscriber privacy and security.
Here's a detailed explanation of S-TMSI:
Mobile Subscriber Identity (MSI):
The Mobile Subscriber Identity (MSI) is a unique identifier associated with a mobile subscriber in a cellular network. It consists of two parts: the Mobile Country Code (MCC) and the Mobile Network Code (MNC), which together identify the network operator, and the Mobile Subscriber Identification Number (MSIN), which uniquely identifies the subscriber within the network.
Temporary Mobile Subscriber Identity (TMSI):
The Temporary Mobile Subscriber Identity (TMSI) is a temporary identifier assigned to a mobile subscriber by the network operator. It is used to establish communication between the subscriber's mobile device and the network while protecting the subscriber's actual identity. The TMSI is periodically changed to prevent tracking of the subscriber's location and activity.
Purpose of TMSI: The TMSI serves several important purposes:
a. Privacy: By using a temporary identifier like TMSI, the subscriber's actual MSI is not exposed during normal network operations. This helps protect the subscriber's privacy by making it more difficult for unauthorized parties to track or identify the subscriber's location or activities.
b. Security: TMSI provides an additional layer of security by preventing unauthorized interception or eavesdropping on the subscriber's communications. Since the TMSI is periodically changed, it becomes challenging for malicious actors to correlate different communication sessions and gain access to sensitive information.
c. Efficient Paging: In cellular networks, when a subscriber receives an incoming call or message, the network needs to locate the subscriber's current location area. By using a TMSI, the network can efficiently perform paging by broadcasting the call or message to the specific location area associated with the TMSI, rather than paging all the subscribers in the network.
S-Temporary Mobile Subscriber Identity (S-TMSI):
The S-Temporary Mobile Subscriber Identity (S-TMSI) is an enhanced version of the TMSI, introduced in the Universal Mobile Telecommunications System (UMTS) and later adopted in Long Term Evolution (LTE) and subsequent cellular technologies.
The S-TMSI is a globally unique identifier assigned by the network operator to a subscriber and is intended to be more persistent than the TMSI. It consists of two parts: the S-TMSI MCC-MNC (similar to the MSI's MCC-MNC) and the S-TMSI Temporary Mobile Subscriber Identity Number (S-TMSI TMSI), which is a unique identifier specific to the subscriber within the network.
The S-TMSI is used in various procedures within the cellular network, such as authentication, location tracking, handovers between cells, and connection establishment. It allows the network operator to maintain continuity of service while providing enhanced privacy and security for the subscriber.
TMSI Reallocation:
To ensure subscriber privacy and prevent long-term tracking, the TMSI is periodically reallocated to mobile devices. When the TMSI is changed, the network sends a TMSI Reallocation Command to the subscriber's device, informing it of the new TMSI. This process helps in minimizing the risk of unauthorized tracking and interception of communications.
In summary, the S-Temporary Mobile Subscriber Identity (S-TMSI) is a temporary identifier assigned by the network operator to a mobile subscriber. It provides enhanced privacy and security by concealing the subscriber's actual identity and preventing tracking of location and activities. The S-TMSI is more persistent than the Temporary Mobile Subscriber Identity (TMSI) and is used in various network procedures to maintain continuity of service while ensuring subscriber confidentiality.