SN id Serving Network Identifier

The Serving Network Identifier (SN Id) is a concept used in telecommunications to identify the serving network to which a mobile device is currently connected. It is primarily used in the context of GSM (Global System for Mobile Communications) and related cellular technologies.

In a GSM network, a mobile device communicates with the network through a specific base station, also known as a cell. Each cell is identified by a unique Cell Global Identity (CGI), which consists of a Mobile Country Code (MCC), a Mobile Network Code (MNC), and a Cell Identity (CI). The MCC and MNC together uniquely identify the network operator, while the CI differentiates between individual cells within the operator's network.

The SN Id is an extension of the CGI and is used to provide additional information about the serving network. It is typically used in scenarios where a mobile device is roaming in a foreign network. When a device roams into a foreign network, it needs to determine the identity of the serving network, including the network operator and the specific network technology being used.

The SN Id is encoded in the Location Area Identification (LAI) field of the Location Area Identity (LAI) information element, which is part of the System Information Broadcast (SIB) messages transmitted by the serving cell. The LAI consists of the MCC, MNC, and a Location Area Code (LAC). The SN Id is derived from the MCC and MNC and provides information about the serving network.

The SN Id can take different forms depending on the specific network technology being used. For example, in GSM networks, the SN Id is represented as a 16-bit value called the Location Area Code Extension (LAC Ext), which is appended to the MCC and MNC. In UMTS (Universal Mobile Telecommunications System) networks, the SN Id is represented by a 28-bit value called the Tracking Area Code (TAC) that is derived from the MCC and MNC.

The SN Id allows the mobile device to identify the serving network and understand the network capabilities and services available. This information is essential for proper network selection and handover procedures, especially in roaming scenarios. By examining the SN Id, the device can determine if the serving network is compatible with the device's capabilities and preferences.

In summary, the Serving Network Identifier (SN Id) is an extension of the Cell Global Identity (CGI) used to identify the serving network to which a mobile device is connected. It provides information about the network operator and the specific network technology being used. The SN Id is encoded in the Location Area Identification (LAI) field and is crucial for network selection and handover procedures, particularly in roaming scenarios.