> This page is for Cloud Call Center. > For clean Markdown of any page, append .md to the page URL. > For a complete documentation index, see https://docs.hams.ai/llms.txt. > For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.hams.ai/_mcp/server. # Extensions > Give each agent an extension with a number and a SIP secret, and set the outbound caller ID and codecs. An extension is an internal number for an agent. An agent needs an extension before the [softphone](/cloud-call-center/softphone) can register. A queue can only deliver a call to an agent who has an extension. The extension number is also the SIP user name of the agent. > **Note** > > Only administrators can change extensions. If you delete an extension, the system removes it from the agent lists of campaigns. ![The Extensions tab with an extension open: the agent it belongs to, its SIP secret, outbound caller ID and codecs.](/_fern-img/8d6034a33467b1e865184bdcc442a6ca1cee89f8c41086576335f9229959ee3f.webp) ## Fields | Field | What it does | Rules | | ------------------------- | ----------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Number (SIP username)** | Sets the extension number. | Required. 4 to 20 digits. Each number needs to be unique in the SIP domain. A queue in the same domain cannot use the same number. You cannot change it later. | | **Display Name** | Sets the display name of the extension. | Up to 128 characters. Do not use a double quote, a backslash, or a line break. For a **User** extension, the name comes from the assigned user. | | **Domain** | Sets the SIP domain of the extension. | Required. You choose it when you create the extension. You cannot change it later. | | **Type** | Sets the kind of extension. | The dashboard shows **User** and does not let you change it. The other values are **Conference** and **Virtual**. | | **User** | Links the extension to an agent. | Required for a **User** extension. One user can have only one extension in a SIP domain. | | **Secret** | Sets the SIP password of the extension. | Required when you create an extension. See [SIP secret](#sip-secret). | | **Outbound Caller ID** | Sets the number that the extension shows on outbound calls. | Optional. Use an optional `+`, then 3 to 15 digits, `*`, or `#`. Up to 32 characters. | | **Codecs** | Limits the audio codecs of the extension. | Choose from `opus`, `PCMU`, `PCMA`, `G722`, and `G729`. | | **Max contacts** | Sets how many devices can register at the same time. | A whole number from 1 to 5. The default is 1. If more devices register, the oldest registration ends. | | **Active** | Turns the extension on or off. | On by default. | ## Create an extension Before you start, make sure that a SIP domain exists and that the agent is a user of the account. See [SIP domains](/cloud-call-center/settings/sip-domains). #### Open the Extensions tab Click **Settings** in the Cloud Call Center sidebar. Click the **Extensions** tab. #### Open the form Click **Create Extension**. The **Create extension** drawer opens. #### Enter the identity Enter the **Number (SIP username)**. Select the **Domain**. Select the **User**. #### Set the secret Click **Generate a strong secret**. Click **Show the secret**. Copy the secret. #### Save the extension Click **Create**. The drawer closes and the extension shows in the list. By default, an account can have 10 extensions. At the limit, the **Create Extension** button is off. The page shows the message "You've reached the extension limit for this account." To change an extension, click its row. Change the fields. Click **Save**. You cannot change the **Number (SIP username)** or the **Domain**. To use a different number, delete the extension and create a new one. ## SIP secret Each extension has a secret. A device uses the secret to register. The system never shows a saved secret again. The drawer shows **Generated — copy it now, it can never be read back** after you generate a secret. The secret must meet these rules: * 12 to 64 characters. Use printable ASCII characters and no spaces. * At least 1 lowercase letter, 1 uppercase letter, 1 digit, and 1 symbol. * At least 5 different characters. * No character 3 or more times in a row. * No 4 sequential characters, such as `1234` or `dcba`. * No common word, such as `password`, `welcome`, or `asterisk`. * No extension number, and no extension number in reverse. To set a new secret, enter it in the **Secret** field or click **Generate a strong secret**. Click **Save**. If you leave the field blank when you edit an extension, the system keeps the current secret. ## Voicemail A **User** extension can have its own voicemail box. The **Voicemail** column shows **On** or **Off**. To set up the box, open the actions menu of the row and click **Voicemail**. For the settings, see [Voicemail boxes](/cloud-call-center/settings/voicemail-boxes). ## Delete an extension > **Warning** > > Check the queues and campaigns that use an extension before you delete it. The system deletes its voicemail box, removes it from all queues, and removes it from the agent lists of all campaigns. You cannot undo a delete. A campaign that has no extension left in its agent list stays in its status and rings nobody. See [Campaigns](/cloud-call-center/campaigns). To delete an extension, open the actions menu of its row. Click **Delete**. Click **Delete** again in the dialog. ## Related * [SIP domains](/cloud-call-center/settings/sip-domains) * [Queues](/cloud-call-center/settings/queues) * [Voicemail boxes](/cloud-call-center/settings/voicemail-boxes) * [Softphone](/cloud-call-center/softphone) * [Campaigns](/cloud-call-center/campaigns)