This is originally a video that I converted into a podcast I think it is still useful 
https://www.youtube.com/watch?v=8D1NAezC-Dk


Notifications have become part of our daily life. We receive them almost every minute on our phones, tablets, and computers. As software engineers, it is good to understand how notifications work, and what different type of notifications there are (push and pull notifications), the advantages and disadvantages of each.    In this video I'll explain how the push notification and pull notification works and the stateful vs stateless nature of each and how it affects the architecture decision of our application that we are building.   

Online diagram tool used in this video: 

Http://www.gliffy.com  

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 -Hussein