A transmitting device and a receiving device are coupled via a high-speed serial interface within a computer system. The transmitting device transmits a packet that includes an extended type/extended length field that extends either a type field or a length field depending on the value of the type field....http://www.google.co.uk/patents/US6944617?utm_source=gb-gplus-sharePatent US6944617 - Communicating transaction types between agents in a computer system using packet headers including an extended type/extended length field
