Message Delivery Options

A message can be delivered in different ways, as shown in Figure 1. Sometimes, a person wants to communicate information to a single individual. At other times, the person may need to send information to a group of people at the same time, or even to all people in the same area.
There are also times when the sender of a message needs to be sure that the message is delivered successfully to the destination. In these cases, it is necessary for the recipient to return an acknowledgment to the sender. If no acknowledgment is required, the delivery option is referred to as unacknowledged.
Hosts on a network use similar delivery options to communicate, as shown in Figure 2.
A one-to-one delivery option is referred to as a unicast, meaning there is only a single destination for the message.
When a host needs to send messages using a one-to-many delivery option, it is referred to as a multicast. Multicasting is the delivery of the same message to a group of host destinations simultaneously.
If all hosts on the network need to receive the message at the same time, a broadcast may be used. Broadcasting represents a one-to-all message delivery option. Some protocols use a special multicast message that is sent to all devices, making it essentially the same as a broadcast. Additionally, hosts may be required to acknowledge the receipt of some messages while not needing to acknowledge others.

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