update and expand SUPL documentation

This commit is contained in:
Daniel Micay 2023-03-06 13:40:50 -05:00
parent 8649a94b53
commit abbafc931b

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@ -1038,14 +1038,30 @@
normally, you can remove the <code>dun</code> APN type from your APN
configuration.</p>
<p>If your chosen carrier includes the <code>supl</code> APN type in their APN
configuration, SUPL will be used to provide A-GNSS in order to greatly improve
location lock time for GNSS (GPS, GLONASS, etc.). The fallback SUPL server is
<code>supl.google.com</code> if the carrier doesn't choose a specific one. You
can remove <code>supl</code> from APN types if you don't want to use this, but
it will greatly increase GNSS location lock time if your carrier lacks control
plane A-GNSS via the cellular network and fully relies on user plane A-GNSS
(SUPL) to provide this instead.</p>
<p>When you have both a cellular connection and Location enabled, control plane
and/or user plane (SUPL) A-GNSS is used in addition to PSDS to greatly reduce
the time needed for GNSS to obtain an initial location lock. These obtain
coarse location info from a server based on nearby cell towers. Control plane
A-GNSS is provided by the cellular connection itself and therefore doesn't
have any real privacy implications while SUPL connects to a server often not
provided by the carrier. Most A-GNSS services only accelerate obtaining a satellite-based
location and won't provide an estimate on their own. The carrier can choose a
SUPL server as part of their carrier configuration but most leave it at the
default of supl.google.com. By default, GrapheneOS overrides the
carrier/fallback SUPL server and uses the supl.grapheneos.org proxy. GrapheneOS adds a
toggle for configuring SUPL in Settings ➔ Location where you can choose
between the default supl.grapheneos.org proxy, the standard server
(carrier/fallback) or disabling it completely. GrapheneOS also disables
sending IMSI and phone number as part of SUPL. Pixels with a Qualcomm baseband
use it to provide both cellular and GNSS including both control plane and user
plane A-GNSS being implemented inside the baseband. For Qualcomm baseband
devices, SUPL is only enabled if the APN configuration for the carrier
includes <code>supl</code> as an APN type. Pixels with a Samsung baseband have
a separate Broadcom GNSS chip without integration between them so SUPL is done
by the OS with regular networking (can use Wi-Fi and VPN) and SUPL is used
regardless of the carrier's APN type configuration. GrapheneOS upgrades the
Broadcom SUPL implementation to only using TLSv1.2 instead of using TLSv1.1
and older.</p>
<p>MMS, RCS, SMS over LTE, VVM (Visual Voicemail), VoLTE (carrier-based calls
on 4G and higher) and VoWi-Fi are largely implemented by the OS via TCP/IP