2 Interface USB 3.0 SuperSpeed
2.5 Burst data transmission

Burst data transmission is a new feature USB SuperSpeed, increasing transmission efficiency by removing the time that we wait for confirmation of each data packet. Each endpoint of SuperSpeed device indicates on its descriptor maximum number of packets that can be send or receive without waiting for their confirmation.

Host enables to dynamically change the number of packets in a burst for each transaction according to its requirements (but cannot exceed the maximum burst size for given endpoint). The host reduces the burst size easily in the case of OUT transactions, in the case of IN transactions sets the burst size using the field in the ACK (ACKnowledge) packets.

Burst data transmission is a function of the SuperSpeed bus enabling to send multiple packets at once without waiting for confirmation of their receipt.

  1. IN TRANSMISSIONS

The terminal device sends data to the host at IN transmissions. The host initiates these transmissions by sending of confirmation IN packet to terminal device that is by using of the included information routed to the terminal device. It also includes information about the expected sequential number of the packet and about the number of expected packets. In response to host the terminal device sends data packets with corresponding sequence numbers.

Although the host must acknowledge the confirmation ACK packet each received data packet, terminal device can send all the requested data packets without waiting for their confirmation.

SuperSpeed IN transmission consists of one or more IN transactions containing one or more packets. It is terminated when all the data was successfully received, the endpoint sends a packet whose size is less than the maximum for given endpoint or endpoint responds with an error.

  1. OUT TRANSMISSIONS

The host sends data to the terminal device at OUT transmissions. The host initiates OUT transmission by sending a continuous stream of data packets to the terminal device. Each data packet contains the information required for routing of the packet and the sequence number of the packet. Terminal device answers by the confirmation ACK packet containing the sequence number of the next expected packet, which also confirms the successful reception of the previous packet.

Like at IN transmissions the terminal equipment must send a confirmation ACK packet for each incoming data packet, but the host on these confirmations ACK packets does not have to wait.

SuperSpeed OUT transmission consists of one or more IN transactions containing one or more packets. It is terminated when all the data was successfully received, the host sends a packet whose size is less than the maximum for given endpoint or endpoint responds with an error.