Delay and jitter in network

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Delay

The time a packet passes through one or more network segments is called latency . From the user's point of view , Delay is the time from the user sending the request to receiving the response from the remote application system . be based on TCP/IP Protocol network transmission includes the following processes ： The router handles 、 User data unit transmission on the network and server processing , Accordingly, there will be routing delay and transmission delay of user data units on the network . Routing delay includes domain name request delay 、TCP Connection establishment and release delays and IP Pathfinding delay .

Classification of delays

In the process of data transmission , Generally speaking, delay is divided into ： Transmission delay , Propagation delay , Processing delay and queuing delay , Packaging delay .
Transmission delay ： The time required to transmit all the bits of all packets to the line , namely PDU The period of time from the end point to the line until the last bit leaves the end point .
Propagation delay ： Every bit in a packet is pushed to the link , This bit propagates to the next hop router . The time required for transmission from the starting point of the link to the next hop router .
Processing delay ： The sum of the time required for the sender and the destination to process data in the process of packet switching , Such as checking the header of the group and the time required to decide where to direct the Group .
Queue delay ： Each packet switching will add data to the buffer queue , every last PDU There may be many packet queues at the destination output of .
Packaging delay ： The protocol layer waits for the application layer to meet PDU Byte traffic of payload length , Then it can be packaged into protocol data units （PDU）. This waiting time is the packaging delay .

shake

Jitter yes QOS A commonly used concept , It means the change degree of packet delay . If the network is congested , Queuing delay will affect the end-to-end delay , As a result, the packet delay transmitted over the same connection is different , And jitter , It is used to describe the degree of such a delay change .
The reason for the jitter ： It is due to the change of various delays that the arrival rate of data packets in the network changes . Network transmission is a complex process , In the middle, it needs to go through routers and different links , The delay experienced by each packet is different . When a packet leaves the sender , Arrange evenly at regular intervals , After passing the network , This uniform interval is destroyed because packets experience different delay sizes , And then there's jitter .

Solution to jitter

1. The queue thread of the jitter cache pointer queue at the packet receiving end receives packets , After sorting the received packets, insert the received packets into the corresponding position of the jitter cache pointer queue .
2. The queued thread timer of the jitter cache pointer queue triggers the queued thread at a certain time interval , The outgoing thread determines whether the packet of the queue head of the jitter cache pointer queue should be out of the queue at the current trigger time , If it is , Then the packet will be sent out of the queue .
3. According to the relationship between the difference between the timestamp value of the tail packet and the head packet in the jitter cache pointer queue and the current jitter cache depth , And according to the relationship between the cache time of the packet in the jitter cache pointer queue and the minimum delay of the packet cached in the jitter cache pointer queue , Increase or decrease the current jitter cache depth .