Connectivity is the idea that two computers in different parts of the world can connect to one another and exchange data. It seems that connectivity is its own reward.
The most common model is two computers connecting with a bidirectional network: one side reads what the other side writes. This operates in both directions and either can close the connection.This is also called Byte Stream Model.
World Wide Web uses HTTP, which is HyperText Transfer Protocol. In HTTP, a client opens a connection to the server and sends requests to it.
HTTP is designed as a document-centric way for program communication. It means the request names a file.
BitTorrent is a program that allows people to exchange large files. A client requests files from other clients. BitTorrent breaks files into pieces and a client can require different pieces from different clients in order to download the complete file. The collection of collaboration clients are called swarms.
BitTorrent starts with a torrent file. The file has information on the file and the tracker that keeps the list of members in the swarm.
Skype protocol uses a reverse connection way to bypass NAT (Network Address Translator). If a client wants to connect to a target client, it asks the server if the target client is connected, and if so let the target client opens a connection to itself. This type server is called Rendezvous.
If both clients are behind the NAT, the Skype protocol uses the Relay server as a data exchange for both clients.