Message Delivery Characteristics First some theory about delivery semantics in messaging systems. When a system wants to communicate via a message broker the developer needs a clear understanding of the delivery semantics. At first one needs to know if and how often a message will be delivered to the broker (and potential consumers): At most once - the message is delivered at most once but also not at all.

Within the scope of some Android R&D I took a look at Google’s Cloud Message Service, GCM. Well, the starter guide at http://developer.android.com/google/gcm/gs.html is almost all you need to get started,…