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The Preferred Roaming List (PRL) is a database residing in a wireless (primarily CDMA) device, such as a cellphone, that contains information used during the system selection and acquisition process. In the case of R-UIM-based CDMA devices, the PRL resides on the R-UIM. The PRL indicates which bands, sub bands and service provider identifiers will be scanned and in what priority order.〔(【引用サイトリンク】url=http://www.phonescoop.com/glossary/term.php?gid=11 )〕〔(【引用サイトリンク】url=http://denbeste.nu/cdmafaq/prl.shtml )〕 Without a PRL, the device may not be able to roam, i.e. obtain service outside of the home area. There may be cases where missing or corrupt PRL's can lead to a customer not having service at all. On many networks, regularly updating the PRL is advised if the subscriber uses the device outside the home area frequently, particularly if they do so in multiple different areas.〔(【引用サイトリンク】url=http://www.androidcentral.com/how-update-your-prl-your-cdma-device )〕 This allows the phone to choose the best roaming carriers, particularly "roaming partners" with whom the home carrier has a cost-saving roaming agreement, rather than using non-affiliated carriers. PRL files can also be used to identify home networks along with roaming partners, thus making the PRL an actual list that determines the total coverage of the subscriber, both home and roaming coverage. The PRL is built by an operator and is normally not accessible to the user. Many operators provide the ability for the user to download the latest PRL to their device by dialing an Over-the-air (OTA) feature code. In the US, this feature code is *228 ( *ACT) for Verizon/MetroPCS/US Cellular and ##873283# (##72786#) for Sprint). In Canada, this feature code is *22803 ( *ACT03) for Telus Mobility. ==PRL structure== The PRL consists of two tables (along with some header and overhead information): : *Acquisition Table – An indexed list of frequencies on which the device may search for particular systems. The idea behind the acquisition table is to optimize the acquisition time by identifying only the frequencies that should be searched, rather than searching the entire frequency spectrum. The information contained in each acquisition table entry includes an index, the network type, and associated channel blocks. : *System Table – A prioritized list of systems that the device is permitted to access (Preferred Systems) and those that it is explicitly forbidden to access (Negative Systems). Note that it is also possible to indicate forbidden systems using a separate SID/NID Lockout List in the handset; however, this is not a recommended approach as it creates control over system selection outside of the PRL. ::Each system table entry belongs to a geographic area known as a GEO. These GEOs are listed in priority order. Each IS-95/1xRTT system is identified by either SID/NID or, in the case of enhanced PRL, SID/NID or MCC/MNC. To support 1xEV-DO systems, the PRL must be IS-683-C or later. Each 1xEV-DO system is identified by a Subnet ID. For hybrid mode operation (i.e. IS-95/1xRTT and 1xEV-DO), association tags are used link an IS-95/1xRTT system with one or more 1xEV-DO systems. Hybrid systems always attempt to select an IS-95/1xRTT system first, then use the association tag to attempt to select an associated 1xEV-DO system. ::Each entry also provides an acquisition table index where the frequencies associated with that system are identified and a roaming indicator that dictates what type of indication should be displayed to the user when they are receiving service from that system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Preferred Roaming List」の詳細全文を読む スポンサード リンク
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