Need some idea.
I have router with 3G internet provider and max overall speed approximately 800 -900k. Main purpose of this router is support IP video surveillance with uploading data stream approximately 400-600k, therefore video surveillance uses main bandwidth of traffic.
How to configure router, if someone start use downloading data and then video data stream will be limited to 128k on next 10 minutes.

Have a look at ques and bursting. By setting bust limit, you can set data to be set back to limit if using more than allocated. Normally set up for few seconds, but guise would work for minutes. Lots of examles and WIKI on this.