#6) IPv6 gives better Quality of Service (QoS) than IPv4
The present IP uses a Datagram service to transfer packets of data between point to point using routers. The IPv4 packet header structure contains 20 bytes of data, such that it contains within the header, all possible options thereby forcing intermediate routers to check whether these options exist and if they do, process them before forwarding them. In the IPv4 packet header, these options have a certain maximum permitted size.
Challenge to IPv4
In IPv4, the Type of Service field or the Differentiated Services Code Point field in the packet header, has a very specific task of classifying the packet and defining what kind of service is expected by the packet, while being delivered through routers across the network. This is typically done through devices in the network, which will classify the packets based on the needs of the particular application. However, this also means that not all QoS-compliant devices are compatible with one another.
How does IPv6 provide a solution?
QoS is given a special boost in the IPv6 protocol with the IPv6 header containing a new field, called Flow Label field that defines how particular packets are identified and handled by the routers. The Flow Label field allows packets that belong to a particular flow, in other words, that start from a particular host and head to a particular destination, to be identified and handled quickly and efficiently by the routers.
The Flow Label Field thus ensures that there is more efficient delivery of information from one end to another without the possibility of it being modified by intermediate systems. This ensures a high degree of QoS especially for peer-to-peer applications like VoIP and other real-time applications.