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--- title: Voice and video concepts in Azure Communication Services titleSuffix: An Azure Communication Services article description: Learn about Communication Services call types. author: sloanster manager: chpalm services: azure-communication-services ms.author: micahvivion ms.date: 05/01/2025 ms.topic: concept-article ms.service: azure-communication-services ms.subservice: calling --- # Voice and video concepts [!INCLUDE [Retirement and breaking changes](../../includes/acs-retirement-breakingchange-callout.md)] You can use Azure Communication Services to make and receive one to one or group voice and video calls. You can make calls to other Internet-connected devices and to plain-old telephones. You can use the Communication Services JavaScript, Android, or iOS SDKs to build applications that enable your users to speak to one another in private conversations or in group discussions. Azure Communication Services supports calls to and from services or bots. ## Call types in Azure Communication Services There are multiple types of calls you can make in Azure Communication Services. The type of calls that you make determine your signaling schema, media traffic flows, and pricing model. ### Voice Over IP (VoIP) When a user of your application calls another user of your application over an internet or data connection, the call is made over Voice Over IP (VoIP). In this case, both signaling and media flow over the internet. ### Public switched telephone network (PSTN) Any time your users interact with a traditional telephone number, the Public Switched Telephone Network (PSTN) voice calling facilitates the calls. To make and receive PSTN calls, you need to add telephony capabilities to your Azure Communication Services resource. In this case, signaling and media use a combination of IP-based and PSTN-based technologies to connect your users. ### One-to-one call A one-to-one call on Azure Communication Services happens when one of your users connects to another user using one of our SDKs. The call can be either VoIP or PSTN. ### Group call A group call on Azure Communication Services happens when three or more participants connect to one another. Any combination of VoIP and PSTN-connected users can be present on a group call. A one-to-one call can be converted into a group call by adding more participants to the call. One of those participants can be a bot. ### Rooms call A call that takes place within the context of a Room. A Room is a container that manages activity between Azure Communication Services end-users. A Room offers application developers better control over *who* can join a call, *when* they meet and *how* they collaborate. For more information, see the [rooms conceptual documentation](../rooms/room-concept.md). ### Supported video standards We support H.264 (MPEG-4) video codec. ### Video quality | Maximum video resolution | WebJS | iOS | Android | Windows | | ------------- | ----- | ----- | ------- | ------- | | **Receiving a remote video stream or screen share** | 1080-P | 1080-P | 1080-P | 1080-P | | **Sending video** | 720-P | 720-P | 720-P | 1080-P | | **Sending screen share** | 1080-P | 1080-P | 1080-P | 1080-P | The resolution can vary depending on the number of participants on a call, the amount of bandwidth available to the client, hardware capabilities of local participant who renders remote video streams and other overall call parameters. ## Next steps > [!div class="nextstepaction"] > [Get started with calling](../../quickstarts/voice-video-calling/getting-started-with-calling.md) ## Related articles - Familiarize yourself with general [call flows](../call-flows.md). - Learn about [Phone number types](../telephony/plan-solution.md). - Learn about the [Calling SDK capabilities](../voice-video-calling/calling-sdk-features.md).