Reach

A message can travel four ways. CHANNEL tries them in order and takes the first one that works: Bluetooth, then direct Wi-Fi, then the local network, then the internet. Each has a letter, and the letter on a message tells you which one carried it.

The first three never leave the room. Only the fourth touches our server, and you can switch it off for a profile under Settings › Reach.

The lights

Four letters sit under a contact's name. They show which paths are open right now. A path you have switched off in Settings is not shown at all.

They are always in the same order, B W L I, and that is the order CHANNEL would try them in. So the leftmost lit letter is the path a message would take if you sent one now. The same order is used in the Reach summary in Settings, and on the letter a message carries once it has gone. Tap the letters in a conversation and one short line explains them above the composer. Tap again and it goes away.

The letters do not all mean the same kind of thing.

• B, W and L mean their phone is in range of yours right now, with CHANNEL awake on it. B is lit when the other phone has been heard from in the last five minutes. A phone that connected to yours counts as heard from, so a phone that cannot announce itself is still reachable. Five minutes with nothing heard and the light goes dark. That is correct: there is nothing there to reach.
• I means the mailbox route works: our server is reachable and they have an address you can post to. It says nothing about whether their phone is awake, because with a mailbox that does not matter. You post now, they collect when they look.

What the local network path costs

L is on when CHANNEL first runs, and it is the one path that says something about you to people who are not your contacts.

To find another phone on the same Wi-Fi, CHANNEL has to announce itself on that network. The announcement carries your phone's own name, the one you set in your phone's settings, because neither iPhone nor Android will let an app leave that part out. So anyone else on the network who looks can see that a device with that name is running CHANNEL.

On your own Wi-Fi at home that tells nobody anything. On a café, hotel, airport or office network it can tie the app to a named person, and on an office network somebody may well be looking.

Nothing is said about who you talk to, and no message is readable. It is the fact that you use CHANNEL, next to your device's name, on that network.

If that matters where you are, switch Local network off in Settings › Reach. The other three paths are unaffected, and messages still reach the same people. It is one tap, and you can put it back when you leave.

The internet is a fallback

A message that goes by radio is not also posted to our server. If any radio can see the contact, the message is offered to those radios alone, and the internet never sees it.

The internet carries a message in two cases:

• No radio can see that contact. There is nothing local to wait for, so it goes at once.
• A radio can see them, but the message has waited longer than that contact's Internet Fallback time.

You set that time on the contact's page: At Once, After 5 Minutes, After 15 Minutes, After 30 Minutes, After an Hour, or Never. A new contact starts at 15 minutes. Never means that person is reached by radio or not at all.

Read receipts, cards and settings updates follow the same rule, with no timer. They go by radio when one can see the contact, and by the internet otherwise.

The cost is worth knowing. If a radio can see them but the write keeps failing, a message for a contact set to 15 minutes can take 15 minutes to leave. Set that contact to At Once if you would rather it went straight out.

Waiting

A contact shows Waiting when nothing can carry a message to them yet: they are not nearby and there is no mailbox for them. CHANNEL never says "no profile" or "not on CHANNEL", because it does not know that, and neither should anyone watching.

Can other phones see this one?

On Android, Settings › Reach shows one line under the Bluetooth switch. It tells you whether this phone is announcing itself, which is how a phone that has never met yours finds it.

• Bluetooth: Visible. Other phones can see this one.
• Bluetooth: This phone cannot advertise. The phone's Bluetooth hardware will not announce. It can still hear other phones, and a phone it connects to can still reach it.
• Bluetooth: No Bluetooth permission. CHANNEL has not been allowed to use Bluetooth. Give it the permission in the phone's own settings.
• Bluetooth: Off. The switch above it is off, or Bluetooth is off on the phone.
• Bluetooth: Failed, with a reason. Something on the phone refused. Turning Bluetooth off and on again is the usual cure.

The iPhone does not show this line.

A text message is not one of the four

Send as Text Message, on a contact's own page, is a different kind of thing. It is a standing choice rather than a path that comes and goes, so it never appears among the letters under a contact's name and it never wins or loses a race against a radio. A message that went that way wears an S of its own.

It is also the one thing in the app that is not sealed. Our server and the phone network can both read a text. See Messages.

Carrying for others

When two phones meet, each can carry sealed mail for contacts the other cannot reach yet, and hand it on later. The carrying phone cannot read what it carries. Settings › Relay › Relay for Others controls whether this phone does so. It is one setting for the whole phone.

English is the reference text; any translation is a convenience. Help is stored on this phone and never contacts anyone.