I always get confused with the word "against"

[fenglish]

Hi,

For the purposes of this paper, where a DMCC device is the only device registered against an extension, we’ll call it a “standalone DMCC device”. Where a standalone DMCC device is used to record calls, we’ll call it a “standalone recording device” .

The above sentence is from a technical document, I found that I always get confused with the word "against", no matter where it appears.
Please help to explain the meaning of "against" in detail.

Thanks.

 

[White Hat]

This is quite technical. One would be able to give you an answer to your question if he/she knew what, at least, "extension" stands for in the text.

 

[White Hat]

Based on what I've managed to gen up on the Internet, there is an extension that works with several units. So the device in question is one of those units.

Max. number of concurrent registrations per extension: This setting controls how many user agents (i.e., phones) can be registered against an extension. This feature is useful if you want to restrict the number of phones that can be registered to an extension. If this field is left blank, the extension will have no limit.

I believe to is a synonym for against, in this case.