QoS (QUALITY OF Service), according to literally translated, it is the quality of service. If the function is explained, it is also possible to call bandwidth control, flow control. The purpose of QoS technology is to effectively utilize limited bandwidth, changing traditional "do-effort" service principles, and realize the on-demand assignment of network bandwidth. From a technical point, a common QoS policy is divided into TOS, IntServ, DiffServ, Traffic Shaper. 1, TOS (Type of Service) Service Type (TOS) is to implement QoS, and TOS fields consist of 8 binary locations by modifying the TOS field, and in the IPv4 data packet header is the 9th to 16th bit. The 0th, 1 and 2 bits in TOS can be used to indicate the relative priority of the packet, the priority range from 0 to 7. The third bit indicates a normal delay or low delay; the 4th indicates a normal throughput or high throughput; the 5th indicates normal reliability or high reliability; the RFC document proposes that a packet can be used in these three options. Two options. The 6th, 7th is retained. No official documentation explains how to use this information, but the network will always discard low priority packets to ensure that high priority packets are transmitted normally, so we can set different priorities to various services to ensure network The reliability of the service, but the priority is limited, and the service in the same priority cannot be distinguished. However, Cisco's network equipment does not utilize the 3rd, 4th, 5th information, and the RFC document 1349 has redefined the 3rd to 6th bits for another 5 parameter options more than 10 years ago. One and any parameters have no help to QoS, and the IPv6 protocol is even more removing the TOS field. Therefore, TOS methods have now been used very much. 2, INTSERV Integrated Services (INTSERV) Provides end-to-end QoS by ensuring a certain bandwidth, requiring each router in the network to support intServ. IntServ provides two levels of QoS: reliable service and controlled loads. Reliable Service Assurance Process enjoys a sufficiently available bandwidth, and the data packets in the queue do not have additional delays. Controlled loads have some traditional IP communication services similar to light load networks, always transmitting each packet as much as possible, but there is no reliable guarantee. One of the INTSERV's question is that the entire network needs to retain related QoS information, which increases the burden of the router, and each node in the network must support intserv. IntServ is suitable for smaller networks. 3, DiffServ Distinguishing Service (DiffServ) solves some of the issues of IntServ and TOS. Diffserv is better, you can work across network. A collection of DiffServ routers formed in the network, called DiffServ cloud. Communication services are classified before entering DiffServ cloud. The biggest advantage of DiffServ is that DiffServ takes boundary operations. Once the communication service enters DiffServ cloud, the router inside the DiffServ does not need to maintain QoS status information, which allows the router to focus on its routing. However, the QoS predictability provided by DiffServ is not very good, and the router inside the DiffServ cloud may change the TOS field to cause errors. The effect of using DiffServ in large LAN or WAN is still good. 4, Traffic Shaper Traffic Shaper Perhaps the most effective QoS implementation method, business traffic shaping product, including Allot Communications, Lightspeed System, PacketEer and Sitara NetWorks, etc. The operation of these devices has independence. After installing these devices, the rest of the network does not need to be changed.
