# Control the Desktop Client from the Web Client

When you switch the Cloud Voice App Web Client into CTI (Computer Telephony Integration) mode, it pairs with a Desktop Client that is signed in under the same extension. From that point the Web Client behaves as an on-screen control panel: you manage each call from the browser, while the audio itself is carried by the Desktop Client.

:::note
CTI simply means your computer controls a phone or softphone instead of you pressing buttons on a handset. In this mode the Web Client sends the commands (dial, hold, transfer, and so on) and the Desktop Client does the actual talking and listening, so the call audio stays on the machine running the Desktop Client.
:::

## When this is useful

Suppose you run a CRM (Customer Relationship Management) system on your office computer and place calls straight from it using click-to-dial in the Web Client, but the CRM can only be reached from inside the office network. If you connect to that office computer remotely from home and dial from the Web Client there, the call audio still travels over the office network rather than your home connection. On an unreliable remote session, that path can lead to choppy or degraded audio.

CTI mode solves this. Install the Desktop Client on your home computer and sign in with your extension, then use the remote session to put the office computer's Web Client into CTI mode so it controls that local Desktop Client. Call audio now flows directly through the Desktop Client on your home machine, so an unstable remote link no longer affects call quality.

## Before you begin

Confirm that the phone system and your apps meet these requirements.

| Component | Requirement |
| --- | --- |
| Phone system | Firmware `84.15.0.74` or later, with the uaCSTA feature turned on. An administrator enables it under **PBX Settings > SIP Settings > Advanced > Other Options > Enable uaCSTA Connection**. |
| Desktop Client | Version 1.5.4 or later, signed in with the same extension you use on the Web Client. |

:::caution
The extension signed in on the Desktop Client must be the exact same extension you use on the Web Client. If the two do not match, the Web Client cannot pair with or control the Desktop Client.
:::

:::note
uaCSTA (User Agent Computer Supported Telecommunications Applications) is the standard that lets one device remotely control call actions on another. It is a system-wide setting that an administrator turns on once, not something you enable from your own account. If switching to Desktop Client mode does nothing, ask your administrator to confirm uaCSTA is enabled and that the firmware is version `84.15.0.74` or later.
:::

## Connect the Web Client to the Desktop Client

1. Sign in to the Cloud Voice App Web Client.
2. In the top-right corner, click the client menu icon ![Cloud Voice App Web Client menu icon](/images/pbx/linkus-web-client.png), then choose **Desktop Client** from the list.

   ![CTI mode selected so the Web Client controls the Desktop Client](/images/pbx/cti-pc-mode.png)

:::tip
After you switch modes, place a quick test call to confirm the Web Client is now driving the Desktop Client. The call controls should appear in the browser while the audio plays through the Desktop Client.
:::

## What you can control

With CTI mode active, you can run these call operations from the Web Client and have them carried out on the Desktop Client:

- Start or end a call
- Place a second call
- Answer or reject an incoming call
- Transfer a call, both attended and blind
- Record a call
- Hold or resume a call
- Swap between held calls
- Add a participant
- Merge calls
- Flip a call
- Transcribe a call