Not very many people realize how much work has gone into the internet. For more than 40 years, protocols have been built on top of each other, countlebs governments and organizations, billions of packets flying across a "series of tubes" and dozens of protocols.
A computer network is a computer system that let independent computers connect with each other through the management of network OS, network software, and network communication protocol to achieve sharing resources and passing the information.
The network Card, it contains the MAC address, which is unique to every card. It is basically used to provide a place for the network cable to plug in, and it also provides some basic processing function.
Bridge functions similarly to Hubs: it also receives network signals and regenerates them. However, it works on a higher level, which means it connects different networks, and avoid the collision(bridge associates MAC addresses with Port). For example, a bridge can connect two local area network A and B: when a device in A wants to pass data to a device in B, the bridge will receive the data from, and then it re-constructs the format of data according B's norm, then transfers the data.
While hubs passing data all the time, bridges only pass data when necessary.
I am gonna go through several protocols that we often heard about.
It is the one of the most important protocols in the internet layer(a higher level). What it does is basically defines a method, such that when packets should be transmitted from a source host to a destination host, IP address and the header is the only things needed. However, it is by nature unreliable, the IP does not really care whether the packets has been successfully transmitted or not, though it tries its best to do it. So in IPv4, some other protocols are used to ensure the reliability.
UDP is a very simple protocol that is designed to link the internet layer and lower layer. It does not require to set a path before sending the data, which is good. Because it is so simple, though it does have a check system to ensure the data integrity, it is still very unreliable. So whenever using it, the loss of packets should be tolerated, such as VoIP, stream media.
When a reliable connection is required, which is the most case, TCP is needed. It is so important, so we often heard about TCP/IP. A three-way handshake is processed during the establishment of a connection to ensure its reliability. I do not plan to go into detail how it works, because there are some awesome jokes that explain this really well in laymen's term.