By default ConfigMgr 2007 Operating System Deployment (OSD) is deploying in Unicast. Every deployment or software distribution will be bit by bit transferred to the device. With ConfigMgr 2007 R2, and specific configuration, Multicast is also possible. Then you can deploy maybe 50 or 100 devices at a time, without the data (bits) being transferred to every device for itself. It's good to know that you have a few possibilities in Multicast, and it's only working in WinPE mode. So what's the advantage of it, with Software distribution in the Task Sequences?
When you talk about Multicast in ConfigMgr R2, there are two types of it. There is a Autocast and Scheduled Multicast possibility. I will describe them both, and explain the differences between them.
Autocast: With Autocast the deployment will start on the first device. When you deploy another device (or more than one) the stream will also be transferred to the other device(s). When the first one is finished, the other device(s) must only pick the other bits for completion. The only thing you have to do for Autocast functionality, is enable Multicast. (screenshot)
Scheduled Multicast: With Scheduled Multicast the deployment will wait for a few minutes or number of clients. The deployment will then start when one of the two conditions are met. The idea behind this, that you have more time to prepare your devices. With this type of deployment the bitstream wil go once over the network, to all your machines that are ready! (screenshot)
For Multicast to get it working, there is a Distribution Point and the Transport server in Windows Deployment Services (WDS) needed. When both are installed and enabled on a Windows 2008 Server, the configuration in ConfigMgr 2007 will take place.
Distribution point: In the ConfigMgr Distribution Point properties you must enable the setting "Allow clients to transfer content from the distribution point using BITS, HTTP and HTTPS". Also on the Multicast tab you must enable the "Enable multicast" setting. Have also a look on the Transfer rate possibility. Ideally this must be set to 100 Mbps or 1 Gbps for a good transfer speed.
When you also want to make use of Scheduled Multicast, you must enable the setting "Enable scheduled multicast" and set the Session start delay (# minutes) and the Minimum session size (# clients). When one of two are met, the deployment will be started (one bitstream).
Image deployment: When you want a succesfull Multicast deployment, the default WIM image must also be Multicast enabled. Open the properties of the WIM image (example: Windows XP SP2), and enable the setting "Allow this package to be transferred via multicast". You can also see here that Multicast functionality is only possible with WinPE (so during the first part of deployment).
When you don't want any Unicast deployment, enable also the setting "Transfer this package only via multicast". Then you are sure that Multicast will be used! Because this will only works in WinPE, there isn't any need to enable this setting on your Software packages. Now there only must be set an advertisement to get it work.
Advertisement: In the advertisement enable the setting "Download content locally when needed by running task sequence". When this is set on: "Access content directly from a distribution point when needed by the running task sequence", Multicast deployment will not work.
Deployment: These are some pictures displayed during deployment. The first one is captured during deployment in Autocast; the second one is captured during Scheduled Multicast.
Because Multicast works only in WinPE mode, you have the choice to put your applications in the default WIM image. Not installing them, but only put the source in it. Then you are still flexible, and make use of full Multicast functionality! Otherwise a part of the installation will be in Multicast, and the other part (applications) will not.
In the Task Sequence don't add your packages with "Install Software", but choose for "Run Command Line". Then put in there the command which is normally placed in Programs - Command Line, for unattended installation. For get it working place the location (e.g. C:\Apps) before the command, and the application will be installed from the local source.
That's all about Multicast for now!