what is cdn

The full name of CDN is Content Delivery Network, which is content distribution network. CDN is a content distribution network built on the Internet. It relies on edge servers deployed in various places and uses the load balancing, content distribution, scheduling and other functional modules of the central platform to enable users to obtain the content they need nearby, reduce network congestion, and improve user access. Response speed and hit rate. The key technologies of CDN mainly include content storage and distribution technology.

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Content storage technology

CDN needs to be considered There are two aspects of content storage issues, one is the centralized storage of content sources, and the other is the distributed storage of content in Cache nodes. Because the scale of content is relatively large and the throughput of content is large, a mass storage architecture is usually used. Currently commonly used storage technologies include direct attached storage (DAS), network attached storage (NAS) and storage area network (SAN).

DAS is a data storage device directly connected to various server or client expansion interfaces. It is completely server-centered and parasitic on the corresponding server or client. It is a stack of hardware without any Storage operating system, network client browses storage device information by accessing the server. NAS can provide high-speed data I/O access, reducing the CPU load borne by the media server due to corresponding data access requests, greatly improving the performance of the media server. NAS puts data on the same server for different users to share. SAN allows servers to share storage devices while still transmitting data at high speed. The shared area network connects servers and storage media through high-speed connections. It has the advantages of high scalability, high availability and strong fault tolerance. It can be easily upgraded and is easy to use. management, helping to improve the cost profile of the entire system.

HFMS is a file storage technology developed for mass storage of streaming media content. In view of the various disadvantages caused by traditional direct file copying, Segment technology is used to transmit newly copied segments in the form of streaming broadcast. The total delay at the end user is within 50ms and is not easily noticeable by the user. In extreme cases, when all users are watching clips from the same popular show at the same time, it can be broadcast simultaneously. HFMS implements segmented storage and services of streaming media content, improving system service performance.

For the storage of VOD content, different storage solutions can be adopted according to the network scale. For small-scale networks, DAS can be used; for medium-sized networks, NAS can be used; for large-scale networks, SAN storage solutions can be used. Based on the characteristics of large data volume and strong real-time nature, it is recommended to use SAN and HFMS combined with storage technology to further optimize streaming media data storage.

Content distribution technology

Content distribution technology reduces the transmission pressure of the IP backbone network through network construction and quickly distributes content connected to the IP network to users terminal. CDN mainly consists of initial servers, cache servers distributed at the edge, redirection DNS servers and content exchange servers. The initial server is responsible for generating server information content; the cache server is responsible for storing part or all of the information content of the initial server; the redirection DNS server provides the user with the nearest server IP address to reduce the pressure on the backbone network; the content exchange server completes the communication between cache servers Load balancing function; the content management server is responsible for the management of content stored in each cache server of the entire network, and formulates corresponding caching strategies for each cache server to improve the service quality of the cache server.

①Segmented distribution technology

Streaming media has no requirements for the integrity of edge content. Nodes only need to store a small amount of programs or program fragments to push content in real time, providing users with complete services. . When the content requested by the user only has partial fragments or no content, the system will use distribution technology to quickly distribute the content.

②Partial distribution technology

Partial distribution technology can improve the hit rate of the edge system. If 10% of the content is fully copied, 20% of the content is copied at 50%, and 50% of the content is copied. Using 10% replication, the system can achieve a hit rate of more than 95%, greatly reducing the load on the backbone network and having superior distribution performance.

Load balancing technology

Load balancing is the core of the entire CDN. The accuracy and efficiency of load balancing directly determines the efficiency and performance of the entire CDN.

Load balancing technology distributes network traffic as evenly as possible to several servers or network nodes that can complete the same tasks for processing, avoiding the unfavorable situation of some network nodes being overloaded while other nodes are idle. Increasing network traffic can also improve the overall performance of the network.

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