In the beginning, the Internet was designed to be a simple communications platform, mainly used to support file transfer and email. Over the past 25+ years, it has grown to be a very complex global communications infrastructure with a multitude of applications and services. IPv4 is based on a simple packet switching model, delivering packets with best effort and no guarantee for delivery. TCP adds guaranteed delivery but has no options to control parameters such as delay and jitter or to do bandwidth allocation.
Emerging multimedia services (such as Voice over IP and videoconferencing) can have significant bandwidth demands and are often very sensitive to timely delivery. The Type of Service Byte (ToS) in the IPv4 header was designed to provide prioritized treatment of certain traffic. However, it was never widely implemented, one reason being that its use would delay the forwarding of packets on routers. As there were almost no real-time services in those days, there was little pressure to find better solutions.
The development of IPv6, combined with the growing demand for real-time servicesand, therefore, Quality of Service (QoS) featureswas an opportunity to look for other solutions. Despite the availability of several different approaches, the topic of QoS is still a matter of research, and there are many ideas under development.
This chapter aims to discuss the features in IPv6 that support QoS.