The Ajax Transport Method
http://www-128.ibm.com/developerworks/edu/x-dw-x-ajaxtrans-i.html

Herrington, Jack D.
IBM
2006

Abstract:

Discover three Ajax data transport mechanisms (XMLHttp, script tags, and frames or iframes) and their relative strengths and weaknesses. This tutorial provides code for both the server side and the client side and explains it in detail to provide the techniques you need to put efficient Ajax controls anywhere you need them.