Internet Protocol Version 4

Addressing

Devices are identified on a network by an address which is a 4-byte number (32 ones and zeroes). For example:

1100 0000 1010 1000 0000 0001 0000 0001

Typically this is written using a notation that is easier to read, by writing each byte as a separate decimal number separated by periods. For example:

1100 0000 -> 192
1010 1000 -> 168
0000 0001 -> 1
0000 0001 -> 1

IP Address: 192.168.1.1

Having identifiers allows for devices to specify who the intended recipient is for the data being sent. This allows the network to be more efficient in transmitting data compared to a network where all data must be delivered to all other devices.

Packets

Data is sent between devices in small chunks called packets which are typically no larger than 1500 bytes. For example, transferring a large file requires the sender to split the data and send many packets and the receiver must then gather the packets and recombine them back into the original file.

If you only have two devices connected together by a dedicated wire, then splitting data into packets isn’t useful, but as the number of devices grows, it becomes infeasible to have every device connected to each other directly. Typically, some devices are only connected to nearby devices and so for information to travel a long distance it must travel over shared wires.

In older communication technology such as analog telephones, a section of wire along the route had to be reserved for the duration of a telephone call and so could only be used by a single telephone call at a time. This made long distance calling much more expensive since the number of wires was limited and if all the wires were in use, the telephone companies would sometimes not allow you to start a new call or would end your call for someone else to use the line instead.

With packets, the wire does not need to be reserved by any single device for a long time since large amounts of information are split up and sent piece by piece. This makes it possible for data coming from many different devices to travel over a single wire by sending a single packet from each device at a time, interleaving data from many devices. At the other end of the wire, the packets are received and then separated again so that they can be forwarded to the correct destinations. This packet switching expanded how many devices the network could handle.

Routing

As the network grows, with more devices, longer distances, and more data, it’s necessary to more efficiently route the data to its destination. To facilitate communication over long distances, some devices act as hubs that receive packets from many nearby devices and forward the packets towards another hub that is closer to the desired destination of a packet. That hub may then also forwarding the packet and so on until the packet finally reaches the destination device. These hubs are called routers.