There are mainly (4) four main QSO operating types: Simple QSO, Group QSO, Network QSO and PileUp QSOs.
1. Simple QSO
When an operator is calling CQ on a clear frequency...
When an operator is calling a specific station on a clear frequency, not in used by anyone...
...makes that frequency belong to the operator.
This means that from that moment on, the operator owns the frequency until he announces QRT = end of operation and clearing the frequency.
Consequently this means that any other station on the frequency have to obey the rules of the owner. It also means that any other station should respect this and not "steal" the frequency by starting to call CQ or calling any of the owners stations without consent so long as the frequency is occupied.
In this type of QSO the normal "His callsign -> My callsign -> Over" protocol should be used as discussed before. (As an example): "SM7NHC, this is 5B4AIT, Over"
The "Over" means the you leave the microphone to the station you addressed.
Breaking a QSO should only be done if you really have something to add to the conversation and the procedure to break into a QSO is to quickly send your callsign between overs. This short "callsign break" should be recognized by the QSO-ing parties and a gap should be left for the breaking station to come in.
2. Group QSO.
In this type of QSO, the conversations are held between more than 2 parties. It may be harder to actually know who started using the frequency, especially if you jump in to an ongoing group QSO. Normally, a group QSO continues as long as there are participants. Same rule about occupied frequency apply, so you cannot just jump in and call CQ or specifically start a personal QSO with someone in the group.
Switching between stations is done by using normal AMateur Radio protocol with the addition "and the group". Such as: "SM7NHC, this is 5B4AIT and the group, over"
Jumping into a group is done in the same way as in the way of breaking normal QSOs as stated above.
If you want to conduct a private QSO with someone in the group, you can break in as stated above and ask a participating station to QSY to another frequency = move to a different frequency. But you should never start a 1 to 1 QSO on a group frequency.
Amateur Radio networks are group QSO's that are controlled by a "Network Control Station" or NCS. The controller or the Chairman should maintain control of the network by starting taking participating callsigns upon the start of the network. Networks could be very rigid or loose depending on their nature. A group QSO could sometimes end up as a network as there are so many participants that a "natural" NCS is chosen.
Networks are mostly started on a specific time and announced in advance.
The normal procedure for a network to operate is: (But can be done in different fashions)
* NCS makes an Introduction of the net such as;
"This is 5B4AIT, HamSphere net control station for the World Wide HamSphere friendship network. This net meets on each Sunday of the Month at 7PM on this frequency."
* NCS collects participant callsigns. So called "check ins".
* NCS assigns "airtime" for participants by calling each station in turn.
* Each participants should participate when called by the network controller, and when ready, leave the microphone back to the controller.
Don't worry if you have nothing to say when the NCS calls you, then just say this: "Your call sign" and "Nothing for the net or no traffic."
* When everyone has contributed to the net, the controller makes a final roundup, perhaps shares some info and declares the net ended.
4. Pile Up QSO's
Whenever there is an interesting station, usually a DX-station (DX = Distant) with a rare callsign or from a rare country, there will be many stations calling in the try to get a confirmed QSO with that stations.
This is called a "pile up". On the Shortwave band one station can have hundreds of users calling him and it is extremely hard to get through.
When there is a "pile up" going on, and you want to make a QSO with such station, special routines are in place. For example. The DX station will only call "his callsign" or "QRZ" only.
QRZ means: Who is calling me?
So when you hear QRZ, you quickly send your callsign but never make a long call.
If you are acknowledged, you will hear the DX-station say: "Your callsign" and a report such as 5/9.
Then say for example: "Roger" or "Thanks for 5/9" and give the DX-station his report such as "You are 5/9" followed by "name is ..." and say "QSL". QSL means "Can you acknowledge reception?"
The DX-station may then say "QSL, thanks for 5/9, 73s and good luck" and he will continue with "QRZ..."
This means that you never should transmit back. The short QSO is over and you have both exchanged reports and callsigns. It may be frustrating as you wanted to speak longer, but you can't as the DX-Station is having a pile up.
I hope that this sheds some light upon the different QSO modes for Amateur Radio.