I am trying to find some information on Client Deployment. I am currently running version 11.06. I have not upgraded to 12.1 as I need to find this information out first. We have a large portion of our client base that is mobile. They use cellular based aircards and cellular modems to access our network through a VPN. My main question is how does a client deployment or a virus definition package react if the client connection is lost. For example, say a virus definition set is roughly 50 percent downloaded to the client, and the client then loses its connection. Does the package start from the beginning when the client reconnects through the VPN, or does SEPM notice that it already has 50% of the download and picks up where it left off?

Hello,

To Answer your Question, when SEP version 12.1 clients are deployed with Packages from SEPM, these packages are created with Latest definitions in it.

So as soon as SEP clients gets installed, the clients are installed with latest definitions.

Now, incase, these clients are Mobile machines, and then connect to the SEPM for definitions however, say incase, they are unable to fetch the entire downloads, then the next time it downloads it would download the same definitions again. 

Ie; It would fetch those days definitions which have not been received by Clients.

Here are few Article for you:

Symantec Endpoint Protection 12.1: Installing the Manager for the first time and deploying clients

http://www.symantec.com/docs/TECH163580

Creating custom client installation packages in the Symantec Endpoint Protection Manager console version 12.1

http://www.symantec.com/docs/TECH165801

Also, 

See About the types of threat protection that Symantec Endpoint Protection provides.

See Configuring client installation package features.

After installation, you can enable or disable the protection technologies in the security policies.

See About enabling and disabling protection.

See Performing tasks that are common to all security policies.

Thanks Mithun for your response. I have been looking through numerous aticles/docs, including the one you posted, however I cannot find anything that describes what happens when a client loses communication during the middle of a client deployment or virus definition update.

when new definitions are downloaded they are stored in 

c:\program files\common files\symantec shared \virus defs.

for every new date; a folder will be create and defs are put inside.

if connection is lost ; I doubt it would still download full defs from the Manager.

For best results it good to configured mobile clients to get from Symantec Liveupdate server using internet as they are always connected to internet one or the other way, this will save your Bandwidth too. when they are away for longer duration

How to configure mobile computers to automatically download virus definitions when disconnected from the Symantec Endpoint Protection Management console

http://www.symantec.com/business/support/index?page=content&id=TECH104571

Hello,

I updated the Comment above...