As I mentioned earlier with IP version 6, faster communication, more secure authenitcation schemes, and utilization of data exchange are a few of the new features. The IPv6 header has been modified quite extensively over the previous v4 to allow these changes. As you can see, IPv6 does not include any unused header space, allowing for faster communication, and less confusion. You also notice the difference in length between the address fields, to support the 128-bit addresses used by IPv6. The Priority field is also 4 bits long, and contains a value indicating the priority of the datagram.
Priority indicates the transmission order.
This field can be used to identify the flow characteristics and provide some adjustment capabilities. The field can also be used to help identify target machines for large transfers, in which case a cache system becomes more efficiant at routing between source and destination. Because it is only 16-bits long, it has a maximum value of 65,535 bytes, but there is a provision for larger datagrams using an extension header. The Hop Limit field is told how many times a datagram can be forwarded from one machince to another. And last, but most important, the Sending and Destination IP address fields.