What is QOS in networking?

We all use different apps like YouTube, Hotstar, Netflix on our mobile phone. These applications use multimedia streaming of data. The nature of streaming data is much different from the nature of normal file transfer. Now a simple thought may come to your mind: What is the difference?

In the case of file transfer, we just need to transfer the bytes from one end to the other end, and whenever we receive all the bytes in the other end, we just combine all the bytes together and reconstruct the file.

On the other hand, in case of multimedia streaming e.g. YouTube streaming (when we watch a YouTube video online) data comes over the Internet and we are playing it simultaneously. While playing the video on YouTube, the video data is getting transmitted continuously from the YouTube server to the client which is running at our browser. You can notice that many a time video got stuck and circular things are rounding (which we call re-buffering).

So for this kind of video transmission, we need to maintain a certain level of Quality of Service(QoS). Qos in the sense that what the other end or the client-side is expecting from the Internet. So, in the case of YouTube video streaming, the youTube client is expecting a continuous stream of videos such that it can render the video directly on the player and play the video without this kind of quality drop or re-buffering. So that is why, to ensure such kind of application quality, we need to provide certain special services at the Internet level.

So, I think now we can clearly understand the definition (from Book):

QoS is the ability of the network to provide better or special service to a set of users and application to the detriment of others.

• “the the ability of the network”-it means that this will be done by network infrastructure i.e., switches and routers. There will be no traffic shaping server, the network infrastructure has to do this job.
• “to provide better or ‘special’ service”,- it means some traffic flow will be given preferential treatment and others will be given what is left over.
• “To a set of users and applications”, -it means which flow should get preference and which will get detriment treatment or less BW
• “To the detriment of others”-it means that since there will be a finite amount of bandwidth if some flow is given more bandwidth there will be less available for the remaining traffic.

Note: Don’t confuse with the offline video downloading which is different from Youtube Streaming. Offline video downloading is just similar to normal file transfer. It is just transferring the video file and playing it offline.