Channel cascade

A cascade is the order of channels through which one message tries to reach the recipient. It starts with the first channel, and if the message is not delivered through it within the chosen time, it tries the next one in line. At the end stands SMS — the channel that needs no app and no data connection and reaches virtually everyone.

That lets you send the message over Viber, RCS or WhatsApp, where it can carry an image, a video and a button, without risking that a recipient who does not have that app gets nothing at all.

How the cascade works

1. The primary channel is sent — the one that stands first in the cascade.
2. We wait until the message lifetime runs out. If the recipient does not take the message within that window, the channel counts as unsuccessful. When it turns out the recipient does not have the channel at all, there is no wait and the cascade moves on right away.
3. The next channel in line is tried, with its own text and its own sender.
4. SMS goes last. It has no lifetime of its own — nothing follows it.

As soon as one channel delivers the message, the cascade ends and the remaining channels are not sent.

Message lifetime

Message lifetime is the time during which the message tries to reach the recipient through one channel. If the recipient does not take it there, the message expires, that channel stops trying to deliver it and the cascade sends the message through the next channel in line.

• It is set for every channel except SMS — for Viber, RCS, WhatsApp and voice messages alike. SMS has no lifetime: it always stands at the end of the cascade, so no channel follows it.
• It counts from the moment the message is sent through that channel, not from the start of the whole cascade.
• It does not apply when the recipient does not have the channel at all. As soon as we find out the recipient does not use that app, the cascade skips straight to the next channel without waiting for the lifetime to run out.
• For Viber and RCS it is passed directly to the channel provider as the message validity, so once it runs out the message stops being delivered on the provider's side too.

How long until the SMS goes out

The individual lifetimes add up. In the worst case — the recipient has every chat app but does not take the message in any of them — the backup SMS goes out only after the lifetimes of all the channels before it have run out. Channels the recipient does not have are skipped without waiting, so the SMS then goes out sooner:

Which value to choose

• As short as possible (even 1 minute) for one-time passwords and verification codes. The recipient is waiting for the code, and after a few minutes it is of no use to them.
• Short (10–15 minutes) for other time-sensitive messages — order dispatch notifications, appointment reminders. A recipient who has the app but does not take the message right away (is offline, has the phone switched off) gets the SMS soon.
• Longer (an hour or more) for marketing campaigns, where what matters most is that as many people as possible see the richer content in the chat app, and a later SMS does not matter.

Why use it

• Deliverability. Not every recipient has Viber, RCS or WhatsApp — the SMS at the end covers the rest.
• Richer content where the recipient can take it. Chat channels carry an image, a video and a button with a link, SMS only text. A cascade lets you offer both in one send-out.
• You only pay for what was really sent. The backup channel is not triggered for a recipient the previous one already delivered to. Channel billing describes this in detail.

Which channels belong in a cascade

A channel you have no registered sender for cannot be ticked in a campaign at all — it is disabled, and for Viber the notice You do not have a registered Viber sender. For more information, please contact our support. appears next to it.

SMS is always last

You decide the order of the other channels yourself, but SMS is moved to the end whatever position you give it. That holds everywhere a cascade is assembled — in a campaign, in the plugin and in the API.

It has three consequences worth counting on:

• SMS has no message lifetime. It is set only for channels that still have something after them.
• SMS is the primary channel only when it is sent on its own. In a cascade with other channels it cannot be primary.
• As the only channel it has no backup. A campaign with SMS alone is an ordinary SMS campaign, not a cascade.

Voice fallback for landlines

SMS reaches almost everyone — landlines are the exception. Neither SMS nor any other channel can deliver a message to a landline. So when we find out that the recipient's number is a landline, we read the message out to them instead: the text is converted to speech (Text to Speech) and delivered to the landline as a voice call. That way the message gets through even to a recipient no channel would otherwise reach.

• It works automatically. There is nothing to set up — the voice fallback is on by default.
• It only affects landlines. Messages to mobile numbers go out unchanged.

What a cascade costs

What gets charged are the messages that are really sent — not every channel in line. When Viber delivers the message, no SMS is created and you pay nothing for it. For a recipient Viber failed to reach, on the other hand, you pay for both: the Viber sent and the SMS that followed.

With Viber, RCS and WhatsApp the credit for an undelivered message is moreover returned to your account once its validity expires. The whole comparison is described in Channel billing.