> For the complete documentation index, see [llms.txt](https://gsm.learn-telecom.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gsm.learn-telecom.com/system-information-messages/system-information-1-si1.md).

# System information-1(SI1)

System Information 1 (SI1) is a message broadcast by GSM base stations to provide critical information to mobile stations (MS). It includes the location area code (LAC), cell identity (CI), and information about neighboring cells. 

This data allows the MS to determine whether it can access the network and helps in the cell selection and reselection processes.

![](/files/cJLu7gM0M5vH5DskPweI)

![](/files/5jqnpvm2pvc7NPYfttwK)

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