What is the process of communication, what are the intentional or unintentional barriers that prevent organizational communication/s to be effective?

What is the process of communication, what are the intentional or unintentional barriers that prevent organizational communication/s to be effective? What a m anager should do to make his communication effective in an organizational set up? Explain with relevant organizational examples and de scribe briefly the organization/s and the situation/ s you are referring to.