Agent linked to DS cannot upgrade from WAN ?

Agent linked to DS cannot upgrade from WAN ?

Hi,
Is anybody can confirm me that a computer agent attached to a distribution server can upgrade its agent version through WAN or it must be done with the Distribution server ?
I mean I have a lot of remote offices, where a distribution server is installed on each client to push the configs/updates. But it happens a lot that some laptops can be fore home office, or for a long out of office period, so the user is at home and has no more connection to the enterprise lan.
So he cannot update its agent version ? He must come to the office to perform the update ?

Please confirm me that its possible because if not, it is a real problem.

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