This topic contains information about how to implement multicast transmissions. If you installed only the Transport Server role service, see the Transport Server topic for information related to multicasting with Transport Server. When you create a multicast transmission, content is transferred over the network only if clients request the data. If no clients are connected (that is, the transmission is idle), then data is not sent over the network.

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Creating multicast transmission for an install image

Creating a transmission

To perform this task, use the following procedure.

To enable multicasting of an install image
  1. Before you create a transmission, you should set the transfer policy for the server. To do this, right-click the server, click Properties, click the Multicast tab, and select an option under Transfer Settings. These settings allow you to enable the following:

    • Multiple stream transfer. The first option under Transfer Settings uses a single stream for all multicast clients, regardless of client speed. The next two options allow you to separate slower clients into their own multicast stream, which enables faster clients to complete their deployment more quickly instead of being held back by slower clients. These settings are only available for clients that boot into a boot image from Windows 7 or Windows Server 2008 R2.

    • Automatic disconnect. The last option under Transfer Settings allows you to automatically stop clients that fall under a specified speed. The clients that are disconnected will continue to transfer the image using unicasting (Server Message Block). These settings are only available for clients that boot into a boot image from Windows Vista with Service Pack 1, Windows Server 2008, Windows 7, or Windows Server 2008 R2.

  2. To create a multicast transmission for an install image, right-click the Multicast Transmissions node (or an install image) and click Create Multicast Transmission. The wizard will walk you through selecting the image and configuring the transmission. There are two types of multicast transmissions:

    • Auto-Cast. This option indicates that as soon as an applicable client requests the image, a multicast transmission of the selected image begins. Then, as other clients request the same image, they too are joined to the transmission that has already started.

    • Scheduled-Cast. This option sets the start criteria for the transmission based on the number of clients that are requesting an image and/or a specific day and time. In addition to these criteria, you can start a transmission manually at any time by right-clicking the transmission and clicking Start. If you do not select start criteria for the transmission, then you must manually start it.

Configuring install image transmissions

After a transmission is created, you can do the following:

  • Start the transmission. If a Scheduled-Cast transmission has at least one client and has not started yet, then you can right-click the transmission and click Start.

  • Delete the transmission. If you right-click the transmission and click Delete, the multicast transmission stops and each client installation reverts to using unicast. That is, the client installations are not deleted or stopped, but they do not use the multicast transmission to complete the installation.

  • Deactivate the transmission. If you right-click the transmission and click Deactivate, each client that is currently installing continues, but no new clients are joined to the transmission. After the last current client installation is complete, the transmission is deleted. If there are no clients when you click this option, then the transmission is deleted immediately.

  • View properties. To view the properties of a transmission, right-click it, and click Properties. Note that you cannot edit the properties of a transmission after it is created. To make a change after you have created a transmission, you need to delete and recreate it.

  • Refresh the transmissions and data. To refresh the data, right-click a transmission and click Refresh, or press F5.

Configuring clients in a transmission

After you have created the transmission, client computers join the transmission by selecting the image in the Windows Deployment Services client. Client computers can also join a transmission using Wdsmcast.exe—a command-line tool included in the Windows Automated Installation Kit (Windows AIK). When there are clients in a transmission, you can:

  • View clients and see progress. To view information about clients that are connected to a transmission, expand the Multicast Transmissions node, and click the transmission. The clients are shown in the right pane.

  • Stop a client installation. To stop the installation completely, right-click a client and click Disconnect. You should use this option with caution because the installation will fail and the computer could be left in an unusable state.

  • Disconnect a client from a multicast transmission. To discontinue the transmission for a particular client but continue to transfer the image through unicast, right-click the client, and then click Bypass multicast.

Creating multicast transmission for a boot image

You can enable multicast transmissions for boot images for computers that use Extensible Firmware Interface (EFI) using WDSUTIL. The following are the commands that you can use to create, start, and remove a transmission. Just like with install images, you can create Automatic-Cast or Scheduled-Cast transmissions. For information about the syntax of these commands, see Wdsutil (

  • Create a multicast transmission.

    • To create an Automatic-Cast transmission of a boot image, run:

      WDSUTIL /New-MulticastTransmission /FriendlyName:"WDS Boot Transmission" /Image:"X64 Boot Image" /ImageType:Boot /Architecture:x64 /TransmissionType:AutoCast

    • To create a Scheduled-Cast transmission of a boot image, run:

      WDSUTIL /New-MulticastTransmission /FriendlyName:"Boot SchedCast Transmission" /Server:MyWDSServer /Image:"X64 Boot Image" /ImageType:Boot /Architecture:x64 /TransmissionType:ScheduledCast /Time:"2006/11/20:17:00" /Clients:10

  • Start a ScheduledCast transmission. To start a previously created ScheduledCast transmission, run:

    WDSUTIL /Start-MulticastTransmission /Server:MyWDSServer /Image:"X64 Boot Image" /ImageType:Boot /Architecture:x64 /Filename:boot.wim

  • Remove a transmission. To remove a transmission but allow all current transfers to complete, run:

    WDSUTIL /Remove-MulticastTransmission /Image:"X64 Boot Image” /ImageType:Boot /Architecture:x64

Additional references