How Data Is Transmitted Over The Internet

What follows is a very qualitative, not technical word about how data is transmitted between computers across the Net through TCP/IP. We will get slightly more precise and technical in the side by side section, for now permit usa address some elementary concepts.

A very basic rule of information (files, due east-mails, web pages et-cetera) transmission across the Internet, and actually a distinctive characteristic of the TCP/IP protocols used to motion information, is that data is never transmitted "as such". Instead, it is subdivided in so-chosen "packets" before manual. The number of the packets depends on the size of the information. For simplicity, let united states of america think about the transmission of a text file. The bigger the file, the more packets will be needed to "represent" the file.

Effigy 1-1-1: Representation of a TCP/IP packet – Source: Wikipedia

If nosotros moving-picture show a file as a train, the packets would exist the individual wagons. Large railroad train: several wagons, small train: few, maybe only one wagon.

Each packet is like an envelope sent past normal mail, with the actual data, office of the original file, inside. Outside, we have information that will allow TCP/IP to process the packet by extracting and merging information technology's within data with the information from the other packets from the same file, in the correct gild, in social club to rebuild the file from it'southward packets. A scheme of a TCP/IP package is shown in Figure one-1-1)

Each package, or envelope if nosotros follow on the previous case, contains the following information: the source of the data (sender), the destination of the information (receiver), information on the source file and on the position of the bundle in this file (say packet 3 of 123 from file X). With this information, one time all the packets for a file have reached the intended destination, they can be used by TCP/IP to rebuild the original file.

Nosotros could summarize the journey of a file such every bit an e-mail message or a web folio, from estimator A to computer B, as follows.

File in computer A –> Subdivided in packets by TCP/IP –> Packets travel, individually, to destination –> TCP/IP "remounts" the packets to re-create the original file in computer B –>File in calculator B

You may notice, in the scheme above, that the fact that packets travel individually is underlined. As we mentioned, communication paths (most often constituted past physical wires) between computer A and figurer F (Figure 1-1) on the Internet are often redundant. Also, these paths are oft non straight (unless A and F are in the same room or the aforementioned building), only rather contain a number or "relays". That is, in club for information to travel from A to F, they might be relayed through B, C, and D (Figure i-1). Physically, on the hardware level, there relays are constituted by Routers. As the proper name implies, routers permit packets to notice the best route betwixt ii computers that do not belong to the same network. Data are generally relayed through several such routers before they accomplish their last destination.

The crucial thing to understand here, is that at any given fourth dimension (nosotros re talking well-nigh milliseconds), the best road between two computers may alter. Routers are able to determine, at the moment of sending a particular packet, the best route at this fourth dimension. When sending the side by side packet, the best road may be different. Therefore, each package from the same file could accept a different route in order to attain the intended destination.

While files are being transferred between 2 PCs, a dialogue goes on between the TCP/IP software of the sender figurer and the TCP/IP software on the receiving computer, aimed at ensuring that the file transfer will be successful. If for example a packet is missing on the receiving side, TCP/IP from this computer volition transport a message to TCP/IP on the sender calculator, request to re-ship a particular packet (this is specifically true for the TCP protocol – other protocols such a UDP work differently). The dialogue will end when all the packets have reached the destination.

Although this parcel organisation might seem circuitous, it has a number of advantages, with respect to an hypothetical model based on sending entire unfragmented files. Kickoff, with a "send unabridged file" model, if something goes wrong, you have to commencement over. Bandwidth is limited, so this would be highly inefficient and would clutter the network. With packets, if something goes wrong with a package, you just have to re-send this bundle, not the whole file. This illustrates well the concept of a "fault-tollerant" organization. 2d, maybe sending a pocket-sized file, could have a very long time, if at that place is a large file existence transferred "before it". Let'southward go back to the image of the train, in which the packets are the wagons. The bandwidth is finite (imagine you simply have one rail). In order to send a small-scale one bundle file (a 1 wagon train), you lot have to look until the big file (a 20 wagon railroad train for case) has passed. If y'all fragment the 20 railroad vehicle train into the individual packets, and send i at a time, then the 1 parcel train has a fair chance to go through together with the packets of the xx wagons railroad train.

As it works now, you tin download your e-mail (50K) while yous download this big video file (700GB). You lot don't accept to wait for the video to download before you tin read your mail. Isn't this great?

This discussion is closely related to the concept of net neutrality. In a condition of neutrality, all packets are equal, and have the same privileges and the aforementioned speed of manual. In a not-neutral situation, a provider might, for example, limit the bandwidth (or make this bandwidth more expensive), for certain kind of packets, for example those related to peer to peer traffic (file exchange betwixt users), or maybe those related to VoIP traffic, for commercial or other purposes.

Let'due south dig further in the next section.