How the Internet Works is a series of articles covering the different aspects of the internet in detail. Not in exhaustive, expert-level detail, like the many books on the subject do, but in enough detail to give a solid understanding … Continued

The internet uses the Transmission Control Protocol/Internetwork Protocol model, or TCP/IP model, to define the way it moves data about. A protocol is a set of agreed-upon rules for behaviors, procedures or communications. In terms of the internet, a protocol … Continued

The physical network is the hardware on which the internet runs. It consists of various connected devices and cables, along with the electrical and radio signals that the devices use to transmit data. While the actual physical media on which … Continued

Bits In physical terms, all digital information is expressed in terms of bits (short for binary digits). A binary digit (a base-two digit) can have a value of either 1 or 0. A bit is the fundamental unit of digital … Continued

A transmission of data begins when a node on a network somewhere requests data from a different network on the internet. Data is transmitted in blocks called frames. The structure of a frame depends on the link protocol that the … Continued

As we mentioned in the previous article, it’s unworkable to use MAC addresses to figure out where to send data between networks. In order to do this efficiently, some sort of hierarchical structure of node identification is necessary. This is … Continued

Routers send traffic from one network to another. Every local network that is part of the internet has at least one router. There are also routers that are not part of a local network, typically those which handle longer internet … Continued

The Link and Internet layers handle transport of data between hosts. However, they do not have a way of differentiating between multiple applications communicating from a single host. Since we don’t want to send emails to browsers or web pages … Continued

The Link and Internet layers do not ensure actual delivery of data. Frames can get lost in transit, and frames can arrive corrupted. So, the process of moving data between two IP addresses is not entirely reliable. The Transport Layer … Continued

TCP guarantees message delivery by implementing four requirements: Delivering segments in the order sent Detecting corrupt segments Retransmission of lost or corrupt segments Elimination of duplicate segments A TCP segment uses four of its fields to implement these requirements: Sequence … Continued