ETSI TS 100 930
Digital cellular telecommunications system (Phase 2+);
Functions related to Mobile Station (MS)
in idle mode and group receive mode
(GSM 03.22 version 7.3.0 Release 1998)

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4.4.3 PLMN selection

The registration on the selected PLMN and the location registration are only necessary if the MS is capable of services which require registration. Otherwise, the PLMN selection procedures are performed without registration.

4.4.3.1 At switch-on or recovery from lack of coverage

At switch on, the MS selects and attempts to perform a Location Registration on the registered PLMN, if it exists. On recovery from lack of coverage, the MS selects the registered PLMN (if it exists) and, if necessary (see subclause 4.6.2) attempts to perform a Location Registration.
If successful registration is achieved, the MS indicates the selected PLMN.
If there is no registered PLMN, or if registration is not possible due to the PLMN being unavailable or registration failure, the MS follows one of the following two procedures depending on its operating mode.
EXCEPTION: If registration is not possible on recovery from lack of coverage due to the registered PLMN being unavailable, a MS attached to GPRS services may, optionally, continue looking for the registered PLMN for an implementation dependent time.
NOTE: A MS attached to GPRS services should use the above exception only if one or more PDP contexts are currently active.

A) Automatic Network Selection Mode Procedure

The MS selects and attempts registration on other PLMNs, if available and allowable, in all of its bands of operation in
the following order:

i) HPLMN (if not previously selected);

ii) each PLMN in the "PLMN Selector" data field in the SIM (in priority order);

iii) other PLMNs with received signal level above -85 dBm in random order;

iv) all other PLMNs in order of decreasing signal strength.

If successful registration is achieved, the MS indicates the selected PLMN.
If registration cannot be achieved because no PLMNs are available and allowable, the MS indicates "no service" to the
user, waits until a new PLMN is available and allowable and then repeats the procedure.
If there were one or more PLMNs which were available and allowable, but an LR failure made registration on those
PLMNs unsuccessful or an entry in a forbidden LAI list prevented a registration attempt, the MS selects the first such
PLMN again and enters a limited service state.
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Что касается диапазона:

3.2 Camping on a cell

3.2.1 Normal camping
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In order to speed up these processes, a list of the RF channels containing BCCH carriers of the same PLMN is broadcast on the BCCH, see subclause 4.8. Also, the MS does not need to search all possible RF channels to find a suitable cell. If, after searching the number of RF channels, given for each frequency band below, with the strongest received signal level, a BCCH carrier has been found but no suitable cell of the selected PLMN has been found, the MS can stop the
attempt to find a suitable cell of the selected PLMN.

The number of channels to be searched are 30 for GSM 900 and 40 for DCS 1800 and PCS 1900.

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4.8 BCCH allocation broadcasting and storage

The BCCH allocation is the list of BCCH carriers in use by a given PLMN in a given geographical area. (It indicates the RF channels that the MS is required to monitor while camped on a cell of that PLMN.) It is broadcast in the system information messages on the BCCH, and is referred to as the BA(BCCH).
When the MS is first switched on in a PLMN, and has no knowledge of which RF channels are BCCH carriers of that PLMN it has to search the strongest RF channels in order to find which are BCCH carriers. It then has to determine which BCCH carriers belong to the selected PLMN. Once it has found a BCCH carrier of the selected PLMN, it can
read the BA(BCCH). It then knows which RF channels to monitor for cell selection and reselection purposes.

Cells supporting GPRS may broadcast a list BA(GPRS) as system information. It indicates the BCCH carriers to be monitored by a GPRS MS for cell re-selection.

Whilst switched on in the PLMN, the MS can gain knowledge of the preferable carriers to use in subsequent cell selections in that PLMN. This knowledge may come from previously decoded BA(BCCH)s and from transmitted information from the network.
When the MS switches off, it has the option of storing the last known BA(BCCH) in a non volatile store so that on a subsequent switch on in that PLMN, it does not need to search to find the BA(BCCH), and so can camp on a cell more quickly. If the BA(BCCH) is stored in the SIM, it shall be stored in the format specified in GSM 11.11. Any other information used by the MS in cell selection shall be stored in a non volatile store on the ME.
The BA(BCCH) may or may not be the total list of BCCH carriers in use throughout the PLMN coverage area. For example there may be differences in different geographical areas, and there may be "umbrella cells" which are only used for hand over traffic and hence are not to be camped on.
NOTE: The PLMN operator cannot expect the ME to store the BCCH carrier frequency of the serving cell in the SIM unless the BA(BCCH) includes the BCCH carrier frequency on which it is broadcast.

A stored BA(BCCH) is not necessarily valid when the MS is switched on again e.g., if the system operator has made a change in BA(BCCH) or if the MS is switched on in a different geographical area. In these cases, the MS may not find a suitable cell for camping on using the stored BA(BCCH). However, the MS may use other stored information to find a suitable cell before searching all the strongest RF channels to find a suitable cell of the selected PLMN.
It should also be noted that the BA(BCCH) only applies to the PLMN on which it was received. If a new PLMN is selected, only a BA(BCCH) previously obtained from that PLMN should be used.
There is another BCCH carrier list, called BA(SACCH), which is sent on the SACCH when in connected mode. This contains the list of BCCH carriers to be monitored by the MS for hand over purposes. The BA(BCCH) and BA(SACCH) need not necessarily be the same. For example, the BA(SACCH) might contain umbrella cells, or the BCCH carrier of the serving cell might be omitted.
If the MS stores a BA list in the SIM, and there is a valid stored LAI, the BA list must be of the PLMN indicated by the stored LAI.

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А теперь понятно? Ищет просматривая определенное число каналов, но во всех диапазонах.

С уважением,
Сергей (id в данной конференции 453)
Мои странички