E-mail clients use POP3 or IMAP4 protocols. Both are "pull" in the sense that the client connects and asks for stuff. When SMTP servers talk to each other, they "push" in the sense that one SMTP server says "Here is the stuff I have for you".
I'm interesting in examples of push and pull semantics. I'm looking for patterns (if they exist) in the use of push/pull from original-producer to final-comsumer in distributed data exchange.
My sense is that pull dominates the final-consumer hop, push dominates the original--producer hop and both push and pull models are common in intermediate hops.