...
- Unacknowledged connectionless mode. This mode allows an entity to send frames either to a single destination, to multiple destinations, or to all destinations on the LAN. The first is referred to as unicast, the second as multicast, and the last as broadcast.
- Connection mode. This mode uses sequence numbers to guarantee frames are (1) arrive to the destination and (2) are ordered correctly upon arrival.
- Acknowledged connectionless mode. This mode is for unicast only (otherwise there could be an undesirably large number of acknowledgements sent in return).
Placement of Layers
Each network protocol has both control information and data. The control information is typically implemented as a header with the data following this header. The data is often referred to as the payload of the header.
...