# Optional Call Center Elements and Attributes

The call center definition file can include optional `<item>` elements in the `<section>` element.

In addition to the required elements, you can add optional elements to configure a softphone.

:::important
The way you implement Open CTI depends on your org’s user interface. There are separate Open CTI APIs for Salesforce Classic and Lightning Experience. The `reqSalesforceCompatibilityMode` item in your call center definition file identifies the user interface you plan to use—Salesforce Classic, Lightning Experience, or both. If no value is specified, the default is `Classic`. This item is optional, but to make calls in Lightning Experience you must specify `Lightning` or `Classic_and_Lightning`.
:::

| <item> Name                      | Description                                                                                                                                                                                                                                                                                                                                                                                                                                      | Supported in Salesforce Classic                                                                              | Supported in Lightning Experience                                                                            |
| -------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------ |
| `reqSalesforceCompatibilityMode` | Determines where the softphone is visible. If no value is specified, the default is `Classic`.<ul><li>To display the softphone in Lightning Experience, specify `Lightning`.</li><li>To display the softphone in Salesforce Classic, specify `Classic`.</li><li>To display the softphone in both user interfaces, specify `Classic_and_Lightning`.</li></ul>                                                                                     | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) |
| `reqStandbyUrl`                  | Represents the location that hosts the secondary softphone. The standby softphone is used after the timeout period for the primary softphone has elapsed and the [notifyInitializationComplete() for Salesforce Classic](/docs/service/api-cti/guide/sforce-api-cti-notifyinitializationcomplete.md) method hasn’t been called within the required timeout period. When you specify a standby URL, you must also specify the `reqTimeout` field. | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) |
| `reqTimeout`                     | Represents the time in milliseconds after which the standby URL is used to host the softphone. Before the timeout period has elapsed, the softphone displays a loading icon indicating that the softphone is initializing. When you specify a required timeout, you must also specify the `reqStandbyUrl` field.                                                                                                                                 | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) | ![Checkmark icon](https://a.sfdcstatic.com/developer-website/sfdocs/service-cloud/media/checkmark_16x16.png) |