Hi friend.
The principles of downloading and uploading from the are described as follows:
1. When the ONT works in routing mode, the ONT establishes a PPPoE tunnel with the BRAS. The ONT encapsulates a PPP protocol header into the upload/download packet, and the BRAS removes the PPP protocol header.
The PC cannot detect the PPP header. Generally, the speed test on a gigabit network interface card or a 100M network interface card does not carry the PPP header.
That is, the processing rate of common IP packets on the WIN operating system is very fast. The PC does not become a performance bottleneck during the uploading and downloading speed test of common performance PCs. For example, the PC can quickly respond to TCP ACK packets during downloading and the PC can quickly send data packets. Therefore, when the ONT works in routing mode, good test results are obtained in both the download speed test and the upper-layer speed test.
2. When the ONT works in bridge mode, the ONT forwards the upload/download packets by hardware only (that is, transparently transmits them). The PC and BRAS establish a PPPoE tunnel. The PC adds PPP headers to all packets sent by the PC. The PPP header needs to be removed when receiving packets.
3. But why is the download performance low in bridge mode? The reasons are as follows:
The PC needs to maintain the PPPoE tunnel. The operating system has poor performance in processing the PPP protocol. The OS needs to parse and remove protocol headers for a large number of received data packets and add PPP headers for sent packets. These operations become performance bottlenecks in the Windows operating system.
Based on cause 1, it takes a long time for the PC to process a large number of data packets. As a result, the TCP ACK response to the server is slow. In this case, the sending rate of the speed test server is suppressed, and the final speed test result is low.
According to experience, the higher the PC performance of the Windows operating system, the better.
4. Why is the upload performance so high?
The PC serves as the data sender. During the test, all the data sent by the PC is false. No packet parsing loss occurs during the test, but only the PPP header loss increases.
In addition, the data received by the PC during the upload speed test is short, that is, TCP ACK packets without data. Therefore, the PC does not need to parse a large number of data packets. Compared with the download, the PC does not need a large number of resources to receive data. Therefore, the performance consumption is reduced.
As the data receiver, the server responds with TCP ACK packets to request the PC to send data. In addition, the intermediate BRAS removes the PPP header.
I hope it is useful for you.
