IPv6 Essentials

Quality of Service in IPv6 Protocols

Given the different QoS paradigms, the designers of IPv6 had to be careful not to impose a specific mechanism, but to provide enough flexibility to support multiple QoS mechanisms. Thus, after much debate and many redesigns, the IPv6 protocols carry a small number of QoS-specific service elements in the IP Base and Extension headers, which can be used in different ways and in several combinations.

IPv6 Base Header

The following section describes the QoS-specific service elements in the IP Base header, namely flows and corresponding flow labels.

Flows

A flow is a sequence of packets sent from a particular source to a particular (unicast or multicast) destination(s), for which the source requires special handling by the intermediate routers. The nature of that special handling can be communicated to the routers by a corresponding control protocol, such as RSVP, or by information within the flow’s packets themselves—e.g., in an IP Base header or a Hop-By-Hop Extension header. There may be multiple active flows from a sender to a receiver, as well as traffic that is not associated with any flow at all. A flow in the IP protocol is uniquely identified by the combination of a source IP address and a non-zero identification, the flow label. Packets that do not belong to a flow carry a flow label of all zeros.

All packets belonging to the same flow must be sent with the same IP source address, IP destination address, and non-zero flow label. If any ...