QoS

The Quality of Service (QoS) refers to the capability of a network to offer a service with a certain quality. The quality of a service can be related to a number of different parameters. Much used parameters are:

• Availability of a link;
• Number of bit errors;
• Latency (delay in the network);
• Jitter.

Which parameter is of importance depends on the service. For example, voice and video services require low latency but tolerate some error rate. By contrast, generic data applications can not tolerate error, but latency is not critical.

The ITU has defined four different categories of services. Each with it's own quality of service associated to it:

• Conversational,
  • Temporal relation preserved,
  • Weak and rigorous delays,
  • Services: Telephony, videotelephony, real time video games;
• Streaming,
  • Temporal relation preserved,
  • Services: Multimedia services;
• Interactive,
  • Demand of response,
  • Data integrity preserved,
  • Services: Internet (web browsing);
• Background,
  • No restraints on delays,
  • Data integrity preserved,
  • Services: E-mail.

This classification is used for instance by 3GPP in the development of UMTS.