Jan 10, 2014

What is the purpose of PRL updates?

In the past month or two I’ve had a notification pop up on my smartphone that the PRL was updated. I have never really noticed anything different about the device afterwards. What does the PRL do that requires regular updating?

Preferred Roaming List

"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. 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. 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# (##UPDATE#) for Sprint). In Canada, this feature code is *22803 (*ACT03) for Telus Mobility."
PRL stands for Preferred Roaming List, and is essentially just a database of towers in your general area and the assets of those towers (3G, 4G, LTE, WiMax, etc.). It also tells your device what it can use, roaming authority, stuff like that. Typically you don’t need to update very often, if ever, but when a carrier is upgrading services and installing new towers, it may be needed to ensure full access. This is probably what you were experiencing when you received push PRL updates. If you are having trouble connecting or getting a poor signal, you can also manually update the PRL on most devices, which may or may not help but, hey, it's worth a shot.
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