GSM MS List of States for the cell selection process
The GSM mobile station (MS) enters various states when switched on, but in the idle mode. Three such states are PLMN selection, cell selection and location registration that GSM standards described as a "set of states". The overall state of the mobile is thus a "composite of the states of the three processes". As TS 100 930 makes mention "In some cases, an event which causes a change of state in one process may trigger a change of state in another process, e.g., camping on a cell in a new registration area triggers an LR request." Below are those states relevant for MS cell selection but for a more detailed description of the behaviour of these states read GSM05.08.
C1 Normal Cell Selection ‑ This is the process of initial cell selection, searching all RF channels.
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C2 Stored List Cell Selection ‑ This is the process of initial cell selection where BCCH carrier information (e.g. a BA list) for the selected PLMN is stored in the MS.
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C3 Camped Normally ‑ This is where the MS is camped on a cell of the selected PLMN and may be able to make and receive calls. (Whether or not the MS can make and receive calls depends on the state within the location registration process). The MS monitors received level and the system information and checks whether cell reselection is needed.
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C4 Normal Cell Reselection ‑ This is where the MS has determined that cell reselection is needed and an attempt is being made to reselect a new cell.
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C5 Choose Cell ‑ This is where the MS has returned to idle mode from "connected mode" and is choosing a suitable cell to camp on.
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C6 Any Cell Selection ‑ This is where the MS is unable to camp normally on any cell of the selected PLMN, or cannot obtain service because of certain responses to a location registration (LR) attempt. It is searching for a cell of any PLMN to camp on (so that emergency calls can be made).
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C7 Camped on any Cell ‑ This is where the MS has camped on a cell irrespective of its PLMN identity, so that emergency calls can be made.
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C8 Any Cell Reselection ‑ This is where the MS is attempting to reselect a cell, irrespective of PLMN identity.
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C9 Choose Any Cell ‑ This is where the MS is returning to idle mode, after having entered "connected mode" from the "camped on any cell" state to make an emergency call. It is attempting to find an acceptable cell to camp on.
