QoS (Quality of Service, Quality of Service) refers to a network that can use various basic technologies to provide better service capabilities for specified network communications. A technology. QoS guarantee is very important for networks with limited capacity, especially for streaming multimedia applications, such as VoIP and IPTV, because these applications often require a fixed transmission rate and are sensitive to delays.
Traditional IP networks treat all messages without distinction. The strategy used by network devices to process messages is First In First Out (FIFO), which allocates the resources required for forwarding according to the order of message arrival time. All messages share resources such as network and device bandwidth. However, the amount of resources ultimately obtained depends entirely on the timing of message arrival. FIFO does its best to send the message to the destination, but does not provide any promises and guarantees for the delay, jitter, packet loss rate, and reliability of the message. Therefore, for some key services (such as voice, video, etc.) Communication quality cannot be guaranteed
With the continuous emergence of new applications on the IP network, new requirements have also been imposed on the quality of service of the IP network. For example, real-time services such as VoIP have imposed higher requirements on the transmission delay of the message. If the transmission delay of the message is too long, , Users will not accept (relatively speaking, E-Mail and FTP services are not sensitive to time delay). In order to support voice, video, and data services with different service requirements, the network is required to be able to distinguish different communications and then provide corresponding services for them. The best-effort service of the traditional IP network cannot identify and distinguish the various communication types in the network, and the ability to distinguish between communication types is the prerequisite for providing different services for different communications. Therefore, the best-effort service model of the traditional network can no longer meet Application needs.
When the network is congested, all data flows may be dropped; in order to meet the user’s requirements for different application and different service quality, the network needs to be able to allocate and schedule resources according to user requirements, and provide different Quality of Service: For real-time and important datagrams, QoS technology is dedicated to solving this problem.
For ordinary data packets that are not very real-time, it provides a lower processing priority and is even dropped when the network is congested. QoS came into being. A device that supports QoS functions can provide transmission quality services. For a certain type of data flow, you can give it a certain level of transmission priority to identify its relative importance and use the various priorities provided by the device. Forwarding strategy, congestion avoidance and other mechanisms provide special transmission services for these data streams. QoS-configured network environment increases the predictability of network performance, and can effectively allocate network bandwidth and make more reasonable use of network resources
Starting from the QoS service model, some of the most used and mature QoS technologies are described one by one. Proper use of these technologies in specific environments can effectively improve service quality.
Generally, QoS provides the following three service models: Best-Effort service (best effort service model), Integrated service (integrated service model, referred to as Int-Serv), Differentiated service (differentiated service model, referred to as Diff-Serv)
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