2 Interface USB 3.0 SuperSpeed
2.6 Packets of USB SuperSpeed Interface

All packets begin on SuperSpeed USB interface by 16-bit header, which can form the entire packet. The packet header starts with packet type information, which is used to determine the method of packet handling. The packet header is protected by a 16-bit CRC (Cyclic Redundancy Check) and it ends by two bytes control word. Most types of packets also comprises the routing information used for routing of the packet from the host.

There are four types of packets on USB SuperSpeed interface:

  • Link Management Packet LMP is sent only between two directly connected ports and it is designed to link control of this connection
  • Transaction Packet TP passes through all the links on the direct route between the device and the host, it is used for control of the flow of data packets, configuration and hubs, it consists only from the header
  • Data Packet DP passes through all the links on a direct route between the device and the host, it has two parts - a data packet header (similar to the transaction packet) and user data in a data packet (it contains data block and 32-bit CRC)
  • Isochronous Timestamp Packet ITP is a packet that it sends by the multicast to all connections in the active state

USB SuperSpeed interface uses four kinds of packets - Link Management Packet LMP, Transaction Packet TP, Data Packet DP and Isochronous Timestamp Packet ITP.