The TCP/IP Guide  9  Networking Fundamentals       9  Fundamental Network Characteristics

Message Formatting: Headers, Payloads and Footers 1 2 Network Structural Models and Client/Server and Peer-to-Peer Networking

Message Addressing Methods

Since the transmission methods above differ based on how many and which devices receive the transmission, they are tied directly to the methods used for addressing:

• Unicast Addressing: Unicast delivery requires that a message be addressed to a specific recipient. This is the most common type of messaging, so this addressing capability is present in almost all protocols.
  
  
• Broadcast Addressing: Broadcasts are normally implemented via a special address that is reserved for that function. Whenever devices see a message sent to that address, they all interprets it as meaning “this message goes to everyone”.
  
  
• Multicast Addressing: Multicasts are the most complex type of message because they require a means of identifying a set of specific devices to receive a message. It is often necessary to create several such groups, which may or may not partially overlap in their membership. Some mechanism is needed to manage which devices are in which groups.

Finally, one special case in the field of addressing is worth mentioning. In some networks or links, only two devices are connected together, forming what is often called a point-to-point network. In this situation, everything sent by one device is implicitly intended for the other, and vice-versa. Thus, no addressing of messages on a point-to-point link is strictly necessary.

Message Formatting: Headers, Payloads and Footers 1 2 Network Structural Models and Client/Server and Peer-to-Peer Networking