To expose your digital assistants and standalone skills to users, you configure channels in Digital Assistant. Channels carry the chat back and forth from users on various messaging platforms to the digital assistant and its various skills. There are also channels for user agent escalation and testing.

You can create and manage the following channel types from the Channels page, which you access by clicking Channels in the left menu. There’s a tab for each type.

You can route each user-facing channel to a single version of a digital assistant or a skill.

Only one version of a skill or digital assistant can run on a channel at any given time. When you create new version of the skill, you can stop the routing to the old version and then assign the routing to the updated version.

You can support running two versions of a skill or digital assistant concurrently by creating separate channels for each one. For example, beta testers could access the skill through one channel while customers continue to chat through a separate channel uninterrupted.

You can use HTML tags to format skill messages, even for channels that have channel-specific markup or markdown. When the message is passed to the channel, the HTML tags you include are replaced with the appropriate markup or markdown for that particular channel. This enables you write messages in one place for multiple channels.

If a tag doesn't have a direct equivalent in a channel, the closest equivalent is used. For example, if the message has <h1>Title 1</h1> and <h2>Title 2</h2> tags, those are converted to *Title 1* and *Title 2* when sent to a Slack channel.

If there isn't a rough equivalent for the tag in the channel, the tags are merely stripped from the message when sent to the channel.

For each channel that you configure, you use the Session Expiration field to set the timeout for inactive user sessions. For most channel types, the default value is one day (1440 minutes). When the session has expired, the conversation is terminated and a message is sent to notify the user of that fact.

In addition, any variables that have been set in a skill's dialog flow will be destroyed, unless the variable was declared as a user-scoped variable. See User-Scoped Variables in YAML Dialog Flows.

If needed, you can break off the current conversations in a user channel by clicking its Reset Sessions button.

To access the Reset Sessions button:

• Click to open the side menu, select Development > Channels, and select the user channel.

From time to time, you may need to disable a channel to perform maintenance or updates to the configuration and then re-enable the channel.

To do so, you can use the these switches:

• Channel Enabled
• Interaction Enabled (for agent integrations)
• Application Enabled (for applications)

Disabling the System channel, which supports the skill tester, alerts developers that the channel is unavailable.

To access these options:

• Click to open the side menu, select Development > Channels, and select the channel.

In addition to the generic elements that you can use in your dialog flows to render across multiple channels, you can also take advantage of features that are specific to a channel type. You can do so through the Common Response component's channelCustomProperties metadata element, which takes the following form:

...
            channelCustomProperties:
            - channel: "CHANNEL_NAME" // can be facebook, slack, cortana, twilio, androidsdk, iossdk, websdk, test
              properties:
                PROPERTY_NAME: "PROPERTY_VALUE"
...

You can apply channelCustomProperties in the component's metadata at the level of globalActions, responseItems, and elements of responseItems, depending on the given property.

Here is an example of custom properties defined at the response item level and the card level:

responseItems:
  - type: "cards"
    cardLayout: "vertical"
    cards:
      - title: "${pizzas.name}"
        description: "${pizzas.description}"
        imageUrl: "${pizzas.image}"
        url: "${pizzas.moreInfo}"
        iteratorVariable: "pizzas"
        channelCustomProperties:
          - channel: "facebook"
            properties:
              webview_height_ratio: "compact"
              fallback_url: "https://www.example.com"
    channelCustomProperties:
      - channel: "facebook"
        properties:
          top_element_style: "large"
..

The channelCustomProperties element takes an array, where each entry specifies the properties of a specific channel. Some custom properties are only applicable to a specific Common Response component element, or even a specific response item type, as in the above example where top_element_style only applies to response items of type cards.

You can also use Freemarker expressions to specify the value of a channel custom property.

Here is an example where a date picker is only shown on Slack when prompted for the expense date item while resolving the composite bag entity expense:

responseItems:
  - type: "text"
    text: "${system.entityToResolve.value.prompt}"
    channelCustomProperties:
      - channel: "slack"
        properties:
          showDatePicker: "${system.entityToResolve.value.name=='Date'}"
...

The available properties vary by channel. See the following topics for the list of custom properties available for each channel:

• Facebook Messenger Channel Extensions
• Slack Channel Extensions
• Adaptive Cards in Microsoft Teams
• Cortana Channel Extensions
• Twilio Channel Extensions
• Oracle Web Channel Extensions
• Oracle iOS Channel Extensions
• Oracle Android Channel Extensions

Here's a non-exhaustive comparison of channels and the features that they support.