The buttons and links on this page now work with the original
permissions and the two new broadcast permissions. Since the new
broadcast permissions have the effect of splitting the `send_messages`
permission this means that additional sections of if/else logic were
required.
The broadcast dashboards contain a button to create a new broadcast.
This adds the new `create_broadcasts` permission as one of the
permissions needed to see the button.
Added two new permissions - `create_broadcasts` and
`approve_broadcasts`. These new permissions get added to the
`has_permissions` decorator of the broadcast routes to allow the routes
to be accessed with either the old permissions on the new ones while we
switch over.
We were using the `send_messages` permission for the broadcast routes.
By having two new permissions we can allow a more granular control of
these routes.
We give estimates of the area for those who can’t see the map. These
estimates were needlessly precise, gave a false sense of accuracy and
were causing intermittent test failures between different environments.
This commit rounds them in the same way that we round the count of
phones.
We had some kind of idea that having this empty page would introduce the
idea of choosing areas and reinforce that you are building up a list of
areas.
But since the journey is now so simple with the button to create an
alert directly on the dashboard page, maybe people don’t need this extra
orientation.
Our current assumption is that the bleed area has the same population
density as the broadcast area.
This is particularly naïve when:
- the bleed area overlaps the sea – no-one lives in the sea
- the broadcast area is a village and the bleed area is the surrounding
countryside
- the broadcast area is adjacent to a densely populated area like a city
We can be smarter about this now that we have a way of determining the
number of phones in an arbitrary area, based on the known areas that we
have population data about.
Calculating the population in an overlap is a slightly more intensive
calculation. So we only doing it for areas which are smaller enough that
it doesn’t slow things down too much. For larger areas we still use the
more naïve algorithm.
Was just in one of those meetings where it felt like writing this would
take less time than I’d already spent talking about its relative
priority…
---
In the admin app you can already set the broadcast channel as 'test', 'severe' or 'government'.
Aim:
- Add the 'operator' channel to the list of channels you can pick for the admin app broadcast services
Note:
- The API already supports this - https://github.com/alphagov/notifications-api/pull/3262
- The CBC proxy does not yet support the operator channel and this will need a separate card. That card has not yet been written because the interface has not been agreed between us and the MNOs yet.
- Will need to have the ability to select the operator channel for just a single MNO like we do for the other channels
- If we add this, we shouldn't actually start using it until the MNO in question gives us the go ahead.
---
https://www.pivotaltracker.com/story/show/178485177
I don’t think we need to say (all networks) in the header. The real
benefit of this change is forcing the platform admin person making the
change to explicitly give their choice of network.
And by not putting it in the label we don’t have future users from other
organisations wondering if there’s some option other than ‘all networks’
they need to think about.
Previously we could only select a provider when using the test
channel, but this is also required for others channels when we
do tests on the production network with individual MNOs.
In order to reduce duplication and improve consistency, I've reused
the new broadcast_service_name_tag macro to show the setting.
This makes the code shareable between:
- the broadcast tour pages
- the broadcast settings platform admin page
- the regular service navigation
On the training mode tour pages we don’t want to confuse people with the
organisation name or _Switch service_ links, so those are omitted and
the code is therefore slightly different.
At the moment if you’re invited to a live broadcast service you get the
training mode tour. This is misleading, and could make people think they
weren’t in danger of sending a real alert.
This commit adds a short, 2 step tour for users invited to a live
broadcast service.
Because we were redirecting in all cases the error message wasn’t being
shown.
This commit changes the endpoint to respond with content (including an
error message) if the `POST` is not successful.
We want people to be really sure before sending a live broadcast, not
just clicking through the green buttons.
This commit adds a checkbox which explains exactly the consequences of
what they’re about to do, tailored to the channel they’re on, and the
area chosen by the person creating the alert.
Adding ‘all networks’ whenever we mention the using the test channel
without a restriction to a single network should help reinforce that
this sends real alerts.
We have been asked to support the government channel so that:
- it can be tested
- the option to use it is available for the most severe of emergencies,
where the public’s choice to opt-out is outweighed by the widespread
risk to life
The current_service.allowed_broadcast_provider is now always "all" or
one of the four providers, which means we can simply the code by not
checking if it is None.
Until all the data is updated to always be "all", we have to handle the
case of provider_restriction being set to None or "all" (which mean the
same thing).
The code can be tidied up once the broadcast provider_restriction is never None.
Do not allow platform admins to:
- create broadcasts
- approve broadcasts
- reject broadcasts
that is, unless they have a send_messages permission
for a given service.
This is so platform admins have the minimum permissions necessary
to cancel a broadcast that might have been sent out accidentally.
We want to know how many phones are in a user-supplied polygon, so we
can show the impact of a broadcast, in the same way that we do when
users pick areas from our library.
We already know how many phones are in each electoral ward. But there
are challenges with an arbitrary polygon:
- where it does overlap a ward, the overlap could be partial
- it could overlap more than one ward
- finding out which wards it overlaps by brute force (looping through
all the wards and seeing which ones intersect with our polygon) would
be way to slow to do in real time
Instead we can use a data structure called an R-tree[1] to build an
index which provides a much, much faster way of looking up which
polygons overlap another. We can build this tree in advance and save it
somewhere, which means there’s a lot of computation we don’t need to do
in real time.
The R-tree returns a set of objects (ward IDs) which we can go and look
up in our library of electoral wards. These wards will be the ones that
might have some overlap with our custom polygon.
Once we have this small set of wards which might overlap our ward, we
can look at the size of the area of overlap (relative to the size of the
whole ward) and multiply that by the known count of phones in that ward
to get an approximation of the count of phones in the overlap area.
Summing these approximations give an estimate for the whole area of the
custom polygon.
1. https://en.wikipedia.org/wiki/R-tree
Now we’ve split the old alerts onto two pages the verbs (‘Broadcast’ and
‘Rejected’) will always be the same for each alert – so they’re not
adding any differentiation.
The specifics of what the datetime means is available on the page for
each alert.
Removing the verbs makes the page a bit less cluttered and makes it
easier to scan down the right hand column.
The code for this page was making assumptions about properties which
aren’t present on rejected broadcasts.
This commit accounts for those properties and presents the relevant
elements on the page.
Two reasons to not hide rejected broadcasts:
- if a broadcast was rejected by mistake then it’s useful to have an
audit of who did that
- it means you can still see old broadcasts without having to leave
in pending-approval, which is dangerous because they might
accidentally be approved
This prevents us from giving unrealistically large or small bleed
estimates in case we have areas which are more dense or less dense than
the most/least dense areas we currently have.
Also means we don’t have to treat City of London as a special case.
There are basically two kinds of 4G masts:
Frequency | Range | Bandwidth
----------|-------------|----------------------------------
800MHz | Long (500m) | Low (can handle a bit of traffic)
1800Mhz | Short (5km) | High (can handle lots of traffic)
The 1800Mhz masts are better in terms of how much traffic they can
handle and how fast a connection they provide. But because they have
quite short range, it’s only economical to install them in very built up
areas†.
In more rural areas the 800MHz masts are better because they cover a
wider area, and have enough bandwidth for the lower population density.
The net effect of this is that cell broadcasts in rural areas are likely
to bleed further, because the masts they are being broadcast from are
less precise.
We can use population density as a proxy for how likely it is to be
covered by 1800Mhz masts, and therefore how much bleed we should expect.
So this commit varies the amount of bleed shown based on the population
density.
I came up with the formula based on 3 fixed points:
- The most remote areas (for example the Scottish Highlands) should have
the highest average bleed, estimated at 5km
- An town, like Crewe, should have about the same bleed as we were
estimating before (1.5km) – Pete D thinks this is about right based on
his knowledge of the area around his office in Crewe
- The most built up areas, like London boroughs, could have as little as
500m of bleed
Based on these three figures I came up with the following formula, which
roughly gives the right bleed distance (`b`) for each of their population
densities (`d`):
```
b = 5900 - (log10(d) × 1_250)
```
Plotted on a curve it looks like this:
This is based on averages – remember that the UI shows where is _likely_
to receive the alert, based on bleed, not where it’s _possible_ to
receive the alert.
Here’s what it looks like on the map:
---
†There are some additional subtleties which make this not strictly true:
- The 800Mhz masts are also used in built up areas to fill in the gaps
between the areas covered by the 1800Mhz masts
- Switching between masts is inefficient, so if you’re moving fast
through a built up area (for example on a train) your phone will only
use the 800MHz masts so that you have to handoff from one mast to
another less often
Broadcasts created by the API are different in that:
- they aren’t created by any user, so don’t have a `created_by_id`
- they are created instantly, not in steps, so don’t have an
`updated_at` time
This commit alters the views to account for when these pieces of
information aren’t present.
