The first octet specifies the type of additional address information. The next octet specifies the length of the address information, from 0 to 255 octets. Its length does not include the two octets that specify type and length. The following octets contain the address information itself, and its format is dependent upon the type of address information. Not all implementations understand this message, and many that do will not honor requests for expedited handling.
Negative numbers indicate expedited handling while higher numbers indicate greater delays.
A priority of 0 is normal. These octets identify the interpretation of the data carried in the packet. Next octets Any data specific to the option set by octet 12 should be specified.