Quality of service (QoS) is very much a missing component of IPv4. When IPv4 was developed, there was no such thing as “mission critical e-commerce data” being exchanged between organizations on the Internet. However, with the rise of B2B e-commerce and the development of digital virtual enterprises, ensuring QoS is critical to the operation of certain classes of applications and services (such as Web Services).
IPv6 provides QoS through a priority and flow label system of packet prioritization defined within the packet header. There are several different priority values that have been suggested for congestion-controlled traffic, which has a lower priority than noncongestion-controlled traffic:
1 Bulk traffic
2 Noninteractive bulk data transfer
4 Interactive bulk data transfer
6 Interactive nonbulk data transfer
7 Control traffic