Push or Pull
You can also divide the different types of communication medium in Push or Pull channels.
Push channels are channels where the sender are pushing the message to the receiver. Meaning it is up to the sender to control the communication.
News letters and letters (if sent out)
Magazines (if sent out)
Pull channels on the other hand is when the receiver is pulling the message from the sender. It is up to the receiver when he or she wants to take in the message.
New letters and letters (if not sent out)
Magazines (if not sent out)
Push channels are often regarded as having higher reliability than pull channels because of the fact that it is more active in the communication.