Best Push technology (from the web server to the browser)

I have an app. that needs the web server to push data to the browser periodically (basically when a stock price updates and the browser must be informed). Events don't occur more than a rate of one a minute and the browser may be set on the page with the information updates for hours on end. The user may be using any of the 'big 5' major browsers.
In ASP.NET, what is the best push technology to send this kind of data to the browser?
Many thanks.
 

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