What is Quality Of Service (QOS) ?

Quality of service models:
  • Best-effort service
  • Integrated services
  • Differentiated services

Best-effort service model – the internet was initially based on a best-effort packet delivery service. Best-effort is the default mode for all traffic. There is no differentiation among types of traffic.
The best-effort model is similar to using standard mail service – it will get there when it gets there.

Advantages of best-effort service model:
  • Highly scalable
  • No special mechanisms required

Disadvantages of best-effort service model:
  • No service guarantees
  • No service differentiation

Integrated services (intserv model) are a QoS model that is older than QOS / Differentiated services model. Intserv model defines a signaling process by which an individual flow can request that the network reserve the bandwidth and delay needed for the flow.

The integrated services model uses RSVP for reserving bandwidth. RSVP stands for a resource reservation protocol. RSVP  is used for reserving bandwidth/QOS tools for a particular flow.
Here is a limitation of intserv model if reserved no other traffic can use it and it is not scalable each flow required separate admin configuration on the router.

The differentiated services model is designed to overcome the limitation of best-effort and intserv models. In Diffserv model network traffic is identified by classes and network QOS policy enforces differentiated treatment of traffic classes. You choose the level of service for each class.

Advantages of Differentiated service model:
  • Highly scalable
  • Many levels of quality are possible

Disadvantages of Differentiated service model:
  • No absolute service guarantee
  • Complex mechanisms

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