Why TCP is not applicable to real-time transmission

 

For real-time transmission (here, real-time transmission mainly refers to interactive video and audio, such as video conferencing and Im video and audio conversations), data volume has the following two features:

1.

Data is generated in real time and sent in real time. If the data cannot be sent within a given period of time, the data will be discarded.

2.

Generally, data traffic transmitted per unit of time is relatively smooth.

TCP
The sliding window is dependent on the sliding window for traffic control. The sliding window size is adaptive and affects the Sliding Window mainly by two factors: network latency and transmission rate. The sliding window size is proportional to the delay, and Transfer Rate
Is proportional. In a given network environment, the latency can be regarded as fixed. Therefore, the sliding window is only related to the transmission rate. When real-time data is transmitted, because the data flow is fixed, the TCP sliding
The dynamic window will be in a small fixed value, which exactly ensures that the current production data is transmitted to the other party in real time. When network packet loss occurs, press the TCP protocol (fast recovery ), sliding Window will be reduced to original
So the transmission rate is halved immediately, and the sending rate is smaller than the data production rate. Some data will stay at the sending end, And the sliding window will keep increasing, until all accumulated data is sent. The above process
This is a typical TCP traffic jitter process, which has a great impact on real-time transmission and may lead to a large burst of latency. From the user's perspective, it is sometimes relatively smooth, but sometimes it gets stuck ("Shake" and compare
Therefore, TCP is usually not used for real-time transmission.