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Old January 6th 19, 09:43 PM posted to
Someone Somewhere Someone Somewhere is offline
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First recorded activity by MobileBanter: Oct 2011
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Default Faster battery drain when roaming?

On 06/01/2019 21:09, S Viemeister wrote:
On 1/6/2019 1:47 PM, MB wrote:
On 06/01/2019 16:30, S Viemeister wrote:
On 1/6/2019 10:16 AM, Woody wrote:
Er, what about those sites in places like the NW of Scotland where
limited UK roaming is applied automatically?
Whereabouts in the NW? I haven't noticed that around the Kyle of Tongue.

I was wondering also.* I think there was talk about it a few years ago
but I did not think it got any further.

I would think it is not too difficult to set up so a phone will
register on any network to make an urgent call.* But then having
handover between cells on a different network and receiving calls from
your own network, might be more complex.* When does the phone decide
to go back to its own network?

I've sometimes seen my phone show 'emergency calls only' when I can't
get a signal on any of my phones. Fortunately, I've not needed to make
an emergency call, so don't know whether it really works.

There are at least 3 procedures at play here -
1. attaching to a network is necessary to make and receive normal calls,
SMS and data.
2. Call handover between cells / areas / networks during a call
3. Emergency Call establishment

The latter is part of the standard and is handled locally by the cell
site as it doesn't require any core network authentication. Of course,
it needs to be switched on at the cell, but it's relatively easy to
support. Phones will show this when they can see networks that they
can't attach to (or are told that they shouldn't attach to by the
preferred network lists) but can't see a network they should be able to
attach to. So in the UK, any other network than your main one.

Attaching to a network "normally" requires authentication and profile
download from the home core network - that requires technical links
(which are also used for inter-network call handling) and commercial
agreements (which I don't believe exist in the UK) from the cell sites.

Call handover is a bit murkier, as the standard mechanisms aren't fast
enough so there are all sorts of special procedures to expedite it
locally which really do not work well between networks or macro cell areas.

So, the net of all this is that emergency calls can work independently,
intra-country roaming could work by commercial agreement, but has the
potential to lead to more dropped calls, more handover attaches between
networks and cell areas and therefore poorer battery life, but of
course the potential for better coverage in edge cases. Roaming can
generally work ok if a preferred network is set in the SIM for that
country, but occasionally a device may take its chances trying to attach
to others, again worsening battery life.

The design of the standards doesn't really allow for attaching to
multiple overlaid networks efficiently as it was felt that each network
would be designed as a singular entity.

Anecdotally, this has other odd effects in countries where networks have
grown by acquisition and you end up with overlaid networks in the same
areas (predominately urban as it was needed for capacity, whereas rural
areas they can just turn off the conflicting cells) and perceived worse
network quality in the city than in the country.