Preferred Roaming List

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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. [1] [2] 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 PRLs can lead to a customer not having service at all.

Removable User Identity Module

Removable User Identity Module is a card developed for cdmaOne/CDMA2000 ("CDMA") handsets that extends the GSM SIM card to CDMA phones and networks. To work in CDMA networks, the R-UIM contains an early version of the CSIM application. The card also contains SIM (GSM) application, so it can work on both networks. It is physically compatible with GSM SIMs and can fit into existing GSM phones as it is an extension of the GSM 11.11 standard.

A service provider (SP) provides organizations with consulting, legal, real estate, communications, storage, processing. Although a service provider can be an organizational sub-unit, it is usually a third party or outsourced supplier, including telecommunications service providers (TSPs), application service providers (ASPs), storage service providers (SSPs), and internet service providers (ISPs). A more traditional term is service bureau.

Roaming is a wireless telecommunication term typically used with mobile devices. It refers to the mobile phone being used outside the range of its home network and connects to another available cell network.

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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. [3] 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.

Cellular network communication network where the last link is wireless

A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called cells, each served by at least one fixed-location transceiver, but more normally three cell sites or base transceiver stations. These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell.

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 United States, for Verizon / MetroPCS / US Cellular, this feature code is *228 (*ACT). For Sprint, it is ##873283# (it is also possible to use code ##72786# on Android or ##25327# on iOS to completely clear out the service programming and redo OTA activation, which includes updating the PRL). [4] In Canada, for Telus Mobility, the PRL update feature code is *22803 (*ACT03).

Over-the-Air programming (OTA) refers to various methods of distributing new software, configuration settings, and even updating encryption keys to devices like cellphones, set-top boxes or secure voice communication equipment. One important feature of OTA is that one central location can send an update to all the users, who are unable to refuse, defeat, or alter that update, and that the update applies immediately to everyone on the channel. A user could "refuse" OTA but the "channel manager" could also "kick them off" the channel automatically.

Cellco Partnership, doing business as Verizon Wireless, is an American telecommunications company which offers wireless products and services. It is a wholly owned subsidiary of Verizon Communications. Verizon Wireless is the largest wireless telecommunications provider in the United States.

Android (operating system) Free and open-source operating system for mobile devices, developed by Google

Android is a mobile operating system developed by Google. It is based on a modified version of the Linux kernel and other open source software, and is designed primarily for touchscreen mobile devices such as smartphones and tablets. In addition, Google has further developed Android TV for televisions, Android Auto for cars, and Wear OS for wrist watches, each with a specialized user interface. Variants of Android are also used on game consoles, digital cameras, PCs and other electronics.

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.

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

  • 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.

PRL modes of operation

The PRL may operate in one of two modes, dictated by a Preferred Only indicator:

  • Permissive Mode (a.k.a. Open PRL, Not Preferred Mode) – The device will attempt to acquire preferred systems; however, if no preferred systems can be located, then the device may select systems that are not listed in the PRL system table. It still will not select negative systems; but, if no preferred systems can be found and an unknown system is available, then it will select the unknown system. While this mode of operation is easier to maintain, because new partners can be chosen even if they are not explicitly listed in the PRL, it carries with it the danger of allowing the mobile device to become camped onto a system that will not provide it with service.
  • Restrictive Mode (a.k.a. Closed PRL, Preferred Only Mode) – The device will only acquire systems identified as preferred in the PRL system table. While this mode of operation gives operators the most control over the system selection process, it requires that PRLs be kept up-to-date to ensure that newly added roaming partners can be selected. Note that even if a PRL is restrictive according to the preferred only indicator, the use of wildcard SID/NID or MCC/MNC values as preferred systems would essentially make the PRL permissive, because wildcards match any system that is located.

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General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Institute (ETSI) in response to the earlier CDPD and i-mode packet-switched cellular technologies. It is now maintained by the 3rd Generation Partnership Project (3GPP).

The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP, UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology. UMTS uses wideband code division multiple access (W-CDMA) radio access technology to offer greater spectral efficiency and bandwidth to mobile network operators.

The international mobile subscriber identity or IMSI is a number that uniquely identifies every user of a cellular network. It is stored as a 64-bit field and is sent by the mobile device to the network. It is also used for acquiring other details of the mobile in the home location register (HLR) or as locally copied in the visitor location register. To prevent eavesdroppers from identifying and tracking the subscriber on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated TMSI is sent instead.

SIM card smart card for a mobile device

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CDMA2000

CDMA2000 is a family of 3G mobile technology standards for sending voice, data, and signaling data between mobile phones and cell sites. It is developed by 3GPP2 as a backwards-compatible successor to second-generation cdmaOne (IS-95) set of standards and used especially in North America and South Korea.

Evolution-Data Optimized

Evolution-Data Optimized is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. EV-DO is an evolution of the CDMA2000 (IS-2000) standard which supports high data rates and can be deployed alongside a wireless carrier's voice services. It uses advanced multiplexing techniques including code division multiple access (CDMA) as well as time division multiplexing (TDM) to maximize throughput. It is a part of the CDMA2000 family of standards and has been adopted by many mobile phone service providers around the world particularly those previously employing CDMA networks. It is also used on the Globalstar satellite phone network.

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Access Authentication in CDMA networks

A UIMID is a 32-bit Electronic Serial Number (ESN) stored in a R-UIM or CSIM used for TDMA or CDMA2000 phones. It is given a different name to avoid confusion with the hardware ESN stored in the phone. In all known systems the UIMID displaces the ESN in signaling. Because the UIMID is allocated from the same numbering space as ESN its existence is transparent to the network. The reason the UIMID is transmitted instead of the ESN is because the card contains the MIN or IMSI and devices such as the HLR running the ANSI-41 mobility management protocol insist on a static association between these identifiers for subscription validation. The HLR will store the MIN or IMSI alongside the ESN in each record, and if an ANSI-41 message is received containing a different pair it will be rejected as invalid.

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A CDMA subscriber identity module (CSIM) is an application to support CDMA2000 phones that runs on a UICC, with a file structure derived from the R-UIM card. By porting the application to the UICC, a card with CSIM, SIM, and USIM can operate with all major cellular technologies worldwide. The CSIM application allows users to change phones by simply removing the smart card from one mobile phone and inserting it into another mobile phone or broadband telephony device supporting the CDMA2000 radio interface.

In telecommunications, a multi-band device is a communication device that supports multiple radio frequency bands. All devices which have more than one channel use multiple frequencies; a band however is a group of frequencies containing many channels. Multiple bands in mobile devices support roaming between different regions where different standards are used for mobile telephone services. Where the bands are widely separated in frequency, parallel transmit and receive signal path circuits must be provided, which increases the cost, complexity and power demand of multi-band devices.

Cellular frequencies are the sets of frequency ranges within the ultra high frequency band that have been assigned for cellular-compatible mobile devices, such as mobile phones, to connect to cellular networks. Most mobile networks worldwide use portions of the radio frequency spectrum, allocated to the mobile service, for the transmission and reception of their signals. The particular bands may also be shared with other radiocommunication services, e.g. broadcasting service, and fixed service operation.

References

  1. ↑ "PRL definition". phonescoop.com.
  2. ↑ "What is a PRL?". USS Clueless.
  3. ↑ "How To: Update your preferred roaming list (PRL) on your CDMA device". androidcentral.com. 2010-10-27.
  4. ↑ "You can update your phone for better service by putting in this code. From 1x to LTE in my house!! : Sprint". reddit.com. 2015. Retrieved 2016-07-19.
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