Broadcast vs. Point-to-point

(Simplex, Half-Duplex, and Full-Duplex)

Broadcast: A method of sending a signal where multiple parties may hear a single sender. A pictured example of this: Imagine a room full of people. In this room, a single person starts yelling some information out. Some people may be sleeping, and not hear the yelling member in this group. Some people may be awake, but not paying attention so they are able to hear the person speaking, but choose to ignore the words that are being said. Another group of people may not only be awake, but be interrested in what is being yelled. This last group is not only able to hear the person speaking, but are also listening to what is being said.
In this example, you can see a single point is broadasting a message to multiple locations that may or may not be able to hear it, and if they are able to hear it, may choose to listen or not.
1. Radio stations are a good example of every day life "Broadcast Network". In this case the radio station is a type of communications called Simplex. (In a simplex type of communication, data is only expected to flow in one direction. In this case, away from the radio broadcast tower.)
2. Board-room meetings are another exeryday example of a broadcast network. In this example, everyone may speak to everyone else, but when more than one person speaks, interference from multiple conversations may make it impossible to listen to more than one conversation even though you can hear both conversations. In this board-room example, we can see parties are able to share access to a common media (human voice as sound through the air.) They compete for access to speak, but for the most part, only one person speaks at a time for everyone to hear. This is an example of a type of communications called Half-Duplex.
3. As a final example of a broadcast network in everyday life, we can see a group of singers attempting to sing in Harmony at a practice. They can each speak separately on their own, but if they speakk on different topics, the conveyed information for any of them may be lost by each other. If we assume that these 4 singers are acting as a "Barber Shoppe Quartet" in a room by themselves, then we may see an example of another type of communication: Full-Duplex. This means that they are not only able to speak, but listen at the same time they are speaking. All of them will speak and listen at the same time. How is this possible? In order to sing in harmony, each singer must be able to hear the frequencies being used by the other singers, and strive to create a frequency with their voice that matches the desiired frequency to create that harmony. This feed-back of each singer to listen to the collective, and possibly key into a specific singer's voice is used by them as they sing to create the exact frequuency needed, and ensure their timing is the same as the rest of the singers. All members are able to hear all other members, and speak at the same time. They are all acting as a Full-Duplex communications in a broadcast network. (I am looking for a better example of a Full-Duplex broadcast system in everyday life.)
Point-to-point: A method of communication where one "point" (person or entity) speaks to another entity. A woman in a resteraunt whispers to her wife a message. Nobody else in the resteraunt know what was said. The conversation was only between one point and another.
Another example that shows a point-to-point network conversation occuring for more than just two peoplecan be seen in examination of the pony express. A single rider takes a bag of mail, and starts riding from the first outpost in a westerly direction until he gets to the second outpost. At the second outpost he changes horses, but keeps riding. Eventually, many hours of changing horses and riding makes him tired, and at one of the stops, he hands off his packacge of mail to the next rider on a new horse. This rider duplicates the process of the previous rider, and continues to travel west. After many changes of riders, many more changes of horses, and a package being carried an handed from one point to another, we see a communication completed. You may look at the rider as being the pieceof data which is carried from one horse to the next in a semi-linear fashion with a westerly direction. You may look at the package and see it as the data being passed from rider to rider as the point to point connection. Whichever item you view as the data, it is being handed off from one part to, and only to, one other party at each transfer point. Nobody else sees the data in the mailbag while it is on transit. This shows data being passed from point-to-point.
1. An example of a very simple simplex point-to-point network could be a doorbell (the circuit.) When the doorbell button is depressed at the front door, a signal is passed to bell or buzzer which performs its functions to announce the button has been depressed. The buzzer, or bell does not send a messagge to to button. The message travels in one direction, and only takes place beteen the button and the buzzer. (We ignore the issue of power consumption, and electron flow for the circuit, since the electrons are not the message.) Another example of a simplex point-to-point communication could be a laser used to signal a message from one point to another. (In this case, we will ignore odd effects and things like prisms that can diffuse, split, and/or partially redirect the beam.)
2. When you have a couple laying on a couch watching a movie, and they are holding hands under a blanket we may see an example of another form of point-to-point communications showing half-duplex. If this couple has their own code in holding hands for speaking to each other that include 3 squeezes maps to "I Love You" (one for each syllable) and 4 squeezes of the hand maps to "I Love You Too" then we set the stage for a dialoge! The wife squeezes her husband's hand 3 times. He gets this message, and smiles (acknowledging the receipt of the message) and then returns a new message of 4 squeezes. She smiles (acknowledging her reciept of the message she felt.) If both parties attempted to squeeze each other's hands at the same time, then the number of squeezes may be confused. So we can see each party may speak through squeezing each others hands, but only one may speak at a time. This conversation takes place only between these two people. Here we see point-to-point and half-duplex.
3. A rather violent and abrupt example of point-to-point Full-Duplex communications can be seen in those old Television westerns when they have a showdown at "high noon" in town. Both of the cowboys have the ability to send messages, in the forms of high velocity projectiles made mostly of dense shiney metallic bullets. They may start transmmitting their messages at the same time, and these messages, are directed from one party to another. The bullet may not suddenly redirect itself to hit multiple targets (like might be possible for a message in a broadcast network, or non-unicast network like multi-cast.) Even when the bullet happens to miss its target, and say stop in the ground, a point to point conversation has taken place. In the case of a bullet hitting the ground, it would only be a simplex conversation since the ground may not throw bullets back.

Comments and/or suggestions for this?: Email me at: dugan@passwall.com
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