What is QoS in Networking?

In this tutorial, we are going to see What is QoS in Networking? The term QoS (an acronym for “Quality of Service”) refers to the ability to provide a service (especially a communication medium) that meets response time and bandwidth requirements.

Applied to packet-switched networks (networks based on the use of routers), QoS refers to the ability to guarantee an acceptable level of packet loss, defined contractually, for a given use (voice over IP, video-conferencing, etc.).

As opposed to circuit-switched networks, such as the switched telephone network, where a communication circuit is dedicated for the entire duration of the communication, it is impossible on the Internet to predict the path taken by the various packets.

Thus, there is no guarantee that communication requiring smooth flow will be able to take place without problems. This is why there are mechanisms, known as QoS mechanisms, which allow to differentiate the different network flows and reserve a part of the bandwidth for those requiring a continuous service, without interruptions.
 

 

Service Levels:

The term “service level” defines the level of requirement for the ability of a network to provide a point-to-point or end-to-end service with given traffic. Three levels of QoS are generally defined:

• Best effort, providing no differentiation between multiple network flows and allowing no guarantees. This level of service is sometimes called lack of QoS.
• Differentiated service (soft QoS), which allows to define priority levels for different network flows without providing a strict guarantee.
• Guaranteed service (or hard QoS), which consists of reserving network resources for certain types of flows. The main mechanism used to obtain this level of service is RSVP (Resource reSerVation Protocol).

 

Quality of service metrics:

The main factors that determine the quality of service are the following:

• Bandwidth: sometimes called bandwidth by abuse of language, it defines the maximum volume of information (bits) per time unit.
• Jitter: it represents the fluctuation of the digital signal, in time or in phase.
• Latency, delay or response time: it characterizes the delay between the transmission and the reception of a packet.
• Packet loss: the non-delivery of a data packet, usually due to network congestion.
• Desequencing: this is a modification of the sequence in which packets arrive.

 
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