In similarity to the telecommunication networks, data communication networks were also circuit switched. The telephone operators developed and ran their own dedicated data communication networks, also known as Wide Area Networks (WAN). These WAN networks usually covered a large geographical area. This type of network could be so big it would fit your entire city.
The idea of packet switching came not too long after the creation of WANs of circuit switching connections. As we know, circuit switching comes in two different variants such as frequency division multiplexing (where we had different channels running on different frequencies) and time division multiplexing (where we had different users taking turns in dedicated time). Packet switching was mostly based on a time division multiplexing, but instead of giving users a set amount of time and set order of turns, it was given a more efficient and dynamic solution. The packet switching method was created to send information that was divided into two parts; the “header” which controlled channel number and length of the packets, and the “payload” which was the information itself. This way you could utilize the capacity better than before, and you wouldn’t have to worry about silent calls where nobody talked, no information being sent and bandwidth is wasted.
The packet’s anatomy.
Here you can see dynamically allocated packets after the demand of the users.
The quality of these physical data communication protocols improved a lot during the years. The integration of Fiber optics especially helped with this improvement. The X.25 technology, which was the first packet switching communication method, had in-built mechanisms for retransmission of incorrect or lost data for every physical link where data was transported over the networks. However, as time went on they found a more simple way of switching of data called Frame Relay, which came not too long after. Frame Relay did not have the retransmission of information but it supported capacity up to 2 Mb/s of data transmission, which is why it quickly substituted the X.25 technology.
After a bit of time, thinking and experimenting, many people thought the “ultimate” solution for data communication became Asynchronous Transfer Mode (ATM). This was just another packet switching technology like Frame Relay and X.25, but the difference is how the packets are divided and switched. Let me explain this a bit better with more pictures.
This is an example of Frame Relay and X.25 technologies. What happens here is that packet 1 is taking up 4 times the capacity and speed than what 2 and 3 would have. This will create a delay for packet 2 and 3 that normally would have arrived much faster.
What happens during ATM is that the exchanging information gets divided into small parts called cells. These cells have a set length of 48 bytes, where the header takes up 5 bytes of that 48 b. This ATM Packet switching technology allows for faster processing time and allows for a more equally distributed data transmission. The great thing with ATM is that it also allows for great quality on telephone networks as well (telecommunication). For a long time, people thought ATM would be the solution for both data communication and telecommunication in our future back in the 90s. However, later during that decade, the introduction to the IP technology grew intensely. It quickly outgrew the ATM technology and has for a long time, even ’till this day, been the main universal technology we all use. ATM is still utilized in some places but is slowly decreasing more and more.