# Control the Web Client from the Desktop Client

The Cloud Voice App Desktop Client includes a CTI mode that links it to the Web Client running under the same extension. CTI stands for Computer Telephony Integration: it lets one program send call-control commands to another. Once connected, the Desktop Client becomes a control surface for placing, answering, and managing calls, while the audio itself flows through the Web Client. This page explains when that arrangement is useful, what you need in place, and how to turn it on.

:::note
"Control surface" means the Desktop Client shows the buttons and call panel, but it does not carry the voice audio. Every call you start or answer from the Desktop Client is actually spoken through the Web Client.
:::

## When to use this

CTI mode helps when the computer running your Desktop Client is not the best place to carry the call audio.

Consider a CRM tool (Customer Relationship Management, the software that tracks your customer contacts) installed on your office computer that you dial from using click-to-dial through the Desktop Client. If that CRM can only be reached from inside the office network, you might connect to the office computer remotely from home to keep working. The catch: when you dial from the Desktop Client on that remote machine, the call audio travels across the office network rather than your home connection, and any instability in the remote session can degrade call quality.

By enabling CTI mode, you can sign in to the Web Client with the same extension on your home computer and let the Desktop Client on the office machine drive it. Calls are still initiated from the familiar Desktop Client interface, but the audio is carried locally by the Web Client on your home computer, sidestepping the unreliable remote link and keeping quality high.

:::tip
The audio always runs through whichever computer is signed in to the Web Client. Sign in to the Web Client on the machine with the most stable local network and a working headset or microphone, and let the Desktop Client on the other machine act as the remote panel.
:::

## Before you begin

Confirm that your phone system and both clients meet these requirements.

| Item | Requirement |
| --- | --- |
| Phone system | Firmware version 84.15.0.74 or later, with the uaCSTA feature turned on (**PBX Settings > SIP Settings > Advanced > Other Options > Enable uaCSTA Connection**). |
| Desktop Client | Version 1.5.4 or later. |
| Web Client | Signed in with the same extension used by the Desktop Client. |

:::note
uaCSTA (user-agent Computer-Supported Telecommunications Applications) is the SIP-based signaling channel that carries the call-control commands from the Desktop Client to the Web Client. **Enable uaCSTA Connection** is a system-wide phone-system setting, so you may need an administrator to turn it on and to confirm the firmware version.
:::

:::caution
The extension signed in to the Web Client must be the exact same extension as the one on the Desktop Client. This has to match on both ends. If the two clients use different extensions, or if the firmware is older than 84.15.0.74, or if uaCSTA is off, the CTI link will not form and the **Web Client** option will not work.
:::

## Turn on CTI mode

1. Sign in to the Cloud Voice App Desktop Client.
2. In the top-right corner, click the CTI icon ![CTI mode toggle](/images/pbx/cti.png), then choose **Web Client** from the drop-down list.

   :::note
   The CTI icon sits at the top-right corner of the Desktop Client window. The same drop-down lets you switch the audio path back to this computer later by choosing the Desktop Client option instead of **Web Client**.
   :::

   
   ![Cloud Voice, selecting Web Client from the CTI menu in the Desktop Client](/images/pbx/cti-web-mode.png)

## What you can do next

With CTI mode active, the Desktop Client controls the following call operations while the Web Client handles the audio:

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