I have seen this questions often in social communities and online forums on this topic and how they work during content download. So i will try to explain what they mean and how they work when it comes to content download.
when you create any deployment (applications,software updates,task sequence etc) ,you will see two options for ‘Type of Deployment’ (for software updates) ,Purpose (for applications) with Required and Available. In this blog post, we will see what they mean and how they work .
Available: Available deployments will not have any deadline and they meant for optional. When you choose the type of deployment as Available ,user can see the deployments in Software Center and it will never be installed automatically unless user select and install it.
When user choose to install the available deployments in Software Center ,it will start downloading the content and install it ,no matter if the client has maintenance window or not as it is initiated by User and it will proceed to install the deployment after the download but if the deployment require reboot ,it will check for MW (maintenance window) and only reboot.
In this type of deployment ,deployments will not be downloaded automatically unless user initiate the deployment.
Required: Required deployment have available time and deadline time. When you create deployment ,you will have to set available time (For clients to download the policies and download the content ) and deadline time (for installation).
When machine policy runs on the client , client will download the policies that are new or updated ,evaluate the policies and inject into wmi.
If you have any deployments with future deadline date but not as soon possible (which means the current time when you do the deployment) ,client will not perform the evaluation of the deployment for content download ,instead it will wait for the deadline date for content download and install (if enough maintenance window available).
In Required deployment ,content download happens only when the deployment reaches/passes the deadline date .Once the download is finished, it will check for enough maintenance window ,if there is ,it will install right after the content download. If there is future maintenance window available ,it must wait for the MW and install it .
If you have set deadline to ‘As soon as possible which means the current time on the site server, client receive the policy ,process it and download the content immediately due to deadline behaviour but for install ,it will check if MW ,if yes,wait for the MW else install the deployment.
My Observation in software updates deployments:
Take an example that ,I have deployed few software update groups to a collection with future deadline date but available time is current date . After 60 min (default ) ,client will receive the new/updated policies ,they process it and inject into wmi --but the content will not be downloaded until it reach the deadline time.
In this case ,all my deployments are set to future deadline date ,so they will never be evaluated by software update deployment evaluation cycle unless the deadline reaches and you will not see the updates in software center. When the deadline time triggers ,patches will be downloaded and install if enough MW available.
you will only see the list of patches available in software center if it is evaluated by software update deployment evaluation cycle and this happens automatically when the deadline reaches or you can initiate the
What happens if the client downloaded the policies but you initiated the deployment evaluation ?
Once the deadline time reached, deployment evaluation starts ,it will pick the policies that are available in client WMI and start processing each update with its compliance check (require,not require or already install) and start download the updates into ccmcache.
In this scenario, the download happens when the deadline reaches but not because of the maintenance window available. Maintenance window is only for the installation of updates but not for download of updates.
For more information about how the maintenance window is calculated, take a look at https://blogs.technet.microsoft.com/charlesa_us/2015/04/21/system-center-configuration-manager-2012-maintenance-windows-getting-to-know-you/
My Observation in Application Deployment:
Like i said how the content download happens for software updates ,it is not same for application Deployment .
For application deployment ,after the deployment to collection with available time as current time and deadline time as future time ,it took random time of 3-4 hours for the application to display in software center and also download happen automatically (Disable deadline randomisation is set to Yes but still it happens after sometime).
Hope You will find this article useful.