There are two main features of download randomization: Upgrade schedule and the distribution timeline.
Upgrade Schedule:

• If selected, this option will limit the packages to a specific time range during the day (i.e. only deploy from midnight to 8am)

Distribute updates over:

• How long to spread out the distribution. If set to '0' updates start right away (or during the next Upgrade Schedule if specified)

How it works:

• You have configured your distribution options, and completed the Upgrade Groups Wizard. As clients check in the SEPM, they will be notified that there is a new update to download and install.

  The SEPM will either tell the client to download the package immediately, or if a schedule/timeline is specified the SEPM will give the client the parameters to download the package (i.e. sometime over the next 4 days between midnight and 8am) and the client picks a random time in that range. There is no visibility from the SEPM to see when a specific client is scheduled to start it's download. If a client is offline when the random window occured, the client will pick a new random time.

** NOTE: There was an issue fixed with SEP 11 MR4 with these features. With MR3 and previous you could only specify an Upgrade Schedule OR a distribution timeline... not both. MR4 and later this issue is resolved

Explanation of Auto-Upgrade Download Randomization in SEP 11 and 12.1

http://www.symantec.com/business/support/index?page=content&id=TECH97073

https://www-secure.symantec.com/connect/articles/upgrade-clients-sep-121-auto-upgrade-feature

Note : You must test the AutoUpgrade process before you attempt to upgrade a large number of clients in your production network. If you do not have a test network, you can create a test group. You can add a few non-critical clients to the test group and upgrade them by using AutoUpgrade. You can confirm the upgrade completed successfully by verifying the version number of the client software that appears in the About dialog box.

Hi Ashish,

thanks much for your instant response, in my case as described above, I have the schedule enabled (the schedule checkbox is ticked), however the time windows for the schedule is 00:00 hours to 23:59 hours which is round the clock, with distribution over 0 days. In this case, clients that are online would pick up this package at random intervals.

Now what happens to the clients that haven't had a check in that day?

Yes,After schedule time SEP client not received package.

If you will be select schedule time bandwidth consume very high during package push.

Even if the client package is not removed from the group, the clients will be prevented from downloading them, right?

Also, I would like to know more about the formula used for this, could you please explain?

Even if the client package is not removed from the group, the clients will be prevented from downloading them, right?

Also, I would like to know more about the formula used for this, could you please explain?

Distribute upgrades over:

• Specifies the number of days or hours over which the packages can be distributed.
• The following formula calculates time:

•  
  • (Package Size\Server Transfer Rate) * Number of Computers

    as

    MB / MB per second * Num = seconds

Reference:

https://www-secure.symantec.com/connect/forums/sep-11061-install-package-upgrade-question

Hi,

1. Now, how is this client package distributed or made available to the clients?

--> It works according to upgrade scheduled, it scheduled is not set then it will start upgrading clients simultaneously.

2. Is it like the upgrade package could be available for download only on the specific of adding it to the group? If so, would the clients that do not check in on the same day but checks in on the next coming days would be denied from downloading this package?

--> I believe answer is 'Yes'.

3.I have also gone through a few other links about this where it was discussed to have formulae based on which the SEPM makes this available to the clients, could some one give an explicit insight on the same?

--> It won't be available to share it on public fourm.

4. Even if the client package is not removed from the group, the clients will be prevented from downloading them, right?

--> If scheduled is set then clients will be prevented from downloading them.