table of Contents
1. The two kinds of loss treatment strategies
In order to ensure real-time, usually adapt to the UDP protocol to transmit data for the RTP, and UDP can not guarantee the quality of data transmission, the network environment in a bad time, packet loss is a recurring problem, what strategies to improve this problem it ?
common methods are: packet loss retransmission (ARQ) and forward error correction (FEC) .
Typically there are two ways the anti-packet loss, FEC and ARQ. FEC redundancy is a forward, for example, transmission data A and B, to increase a transmission data A and B is equal to C XOR. The recipient received packets which any two of the three packages, XOR can be obtained at the third packet. Of course, the actual FEC is not so simple, there is usually more complex matrix operations. ARQ packet loss is the recipient, the sender to request retransmission.
2. Forward Error Correction (FEC)
FEC delivery simple and requires only one-way transmission can support a small delay, packet loss rate fluctuations drawback is when the big, anti-poor packet loss.
FEC is the essence of XOR. If there are four data, then they can take four different values, or, wherein each additional data may consist of four exclusive OR calculated. ABCD and E can also think of a data packet, if we transfer ABCD four packets, the fifth packet transmission is E, five packets can lose any one packet. After the recipient receives the data, it is possible to recover lost data out of it. Forward error correction algorithms can process continuous data is lost in only one packet. At the same time the loss of A and B, the algorithm can not solve.
3. The packet loss retransmission (ARQ)
ARQ advantage is that the network carrying high, with a delay, the case when a large delay or congestion packet loss, can not use ARQ. When congestion loss, using ARQ transmission volume will increase, leading to congestion worse.
Is carried out primarily determines whether the packet loss according to the RTP sequence number (Sequence Number), a sequence number is normally continuous.
[references]
- On the Style Network salon wonderful insider |. Tencent audio and video transmission technology to decrypt (on) https://www.jianshu.com/p/93d2935ab7ed
- Two kinds of loss treatment strategies: packet loss retransmission and FEC (forward error correction) https://www.jianshu.com/p/6157e120ef99