NetEngine AR600, AR6100, AR6200, and AR6300 V300R019 CLI-based Configuration Guide - Virtualization
Understanding WOC
TCP Optimization
Currently, the most widely used transport protocol in a WAN is the TCP protocol. When TCP is used for data transmission, the amount of data transmitted from one end to the other is limited by the datagram window size. When the window is full, the transmitter cannot send more data until the receiver has acknowledged that part of the data in the window has been received. If the datagram window is too small, the data transmission and response rate will be affected.
The congestion control optimization technology in WOC enables the devices at both ends to negotiate to change the congestion control mode from fast reduction of the window size to fast increase and slow reduction of the window size upon a transmission error. In this way, the proper window size can be quickly found when a network error occurs, reducing the transmission time. This technology is mainly used in upper-layer services such as ERP.
- Implements precise flow control and perceives real-time delay and historical bandwidth to achieve smooth and stable data transmission.
- Adds PKT SEQ to work with the original SEQ to quickly identify and locate packet loss by using the dual-SEQ mechanism.
- Changes the TCP push model to the push-pull model, enabling the transmitter to push data and the receiver to send a NACK (negative acknowledgement) to proactively identify and obtain lost packets.
- Breaks through the traditional mode of receiving and triggering ACK and uses periodic acknowledgement (PACK) to quickly synchronize the receive and transmit rates, packet loss rate, receiving acknowledgment number, and head-of-line blocking (HOLB) packet number.
FEC Optimization
The transport layer protocols used for real-time audio and video interaction on the Internet include TCP such as Real-Time Messaging Protocol (RTMP) and UDP such as Real-Time Transport Protocol (RTP). TCP provides reliable data transmission between two endpoints. If the transmitter does not receive an acknowledgment packet, this data block is retransmitted. When real-time audio and video data is transmitted over the Internet, a delay occurs. When the packet loss rate on the transmission channel is high, the TCP transmission quality deteriorates quickly, and the audio and video delay is large due to retransmission congestion. As a result, the audio and video are suspended and then fast played. The improvement of UDP performance cannot guarantee data integrity. Common problems facing UDP are that datagrams may arrive out of order, appear duplicated, or go missing without notice.
Forward Error Correction (FEC) can be used for packet loss recovery. The source (transmitter) encodes data in a redundant way using error correcting code. The destination (receiver) recognizes it and corrects the errors without requiring a retransmission, which ensures the upper-layer audio and video services.