Four key technologies CDN

As broadband networks and the rise of broadband streaming media applications, CDN (content distribution network is usually referred to as Content distribution network, sometimes called content delivery networks Contentdeliverynetwork) as a way to improve Internet content, especially streaming media content delivery to improve service quality, and save network bandwidth backbone technology, at home and abroad are more widely used. The key technology
CDN routing technology with content, content distribution technology, content storage, content management technology.
content routing technology
CDN CDN load balancing system to achieve the contents of routing. Its role is to guide the user's request for the best overall CDN network nodes. Best node selected according to a variety of strategies, such as the nearest, and so the lightest load nodes. Load-balancing system is the core of the CDN, load balancing accuracy and efficiency of the entire CDN directly determine the efficiency and performance.
usually load balancing can be divided into two levels: Global Load Balancing (GSLB) and local load balancing (SLB). Global Load Balancing (GSLB) The main purpose is to network within the user's request directed to the nearest node (or regional). Therefore, the Judgement is near the main functions of global load balancing. Generally confined to certain local load balancing within the area, whose goal is within the scope of a particular region of a Taiwan Xunzhao the most suitable of the nodes provide services, CDN nodes of healthy sex, load, Supported multimedia formats Deng operational status, Local load balancing the main basis for decision-making.
load balancing can be achieved through a variety of ways, the main methods include DNS, application layer redirection, redirect the transport layer and so on.
for global load balancing, in order to judge the implementation of proximity, usually in two ways, one is a static configuration, for instance, a static IP address configuration table to the CDN node IP address mapping. Another way is dynamic testing, such as CDN node detection in real time so that the distance to the target IP (can be used RRT, Hops as a unit of measurement), and then compare the results of detection load balancing. Of course, static and dynamic way can also be used together.
for local load balancing, in order to implement effective policy-making requires real-time access to Cache equipment condition. There are two ways to obtain one is active detection, one is interaction of the protocol. Active detection equipment for the SLB device and there is no agreement Cache interactive interface conditions, such as through the ping command initiate detection, according to the results of the state return. The other is the interaction of the protocol, that is, SLB and Cache real-time according to predefined protocols to exchange operational status information for load balancing. In contrast, interaction of the protocol to be accurate and reliable than the detection methods, but there is currently no standard protocol, the realization of the manufacturers generally only private agreements, exchange more difficult.

content delivery content distribution technology from the content source that contains the edge of the Cache to the CDN process. From the implementation point of view, there are two kinds of mainstream content distribution technology: PUSH and PULL.
PUSH is an active distribution technology. Usually, PUSH initiated by the content management system, content from the source or center of the media resource library distributed to the edge of the Cache node. Distribution of the protocol can use HTTP / FTP and so on. PUSH content distributed by a more general focus of content, which means pre-circulated through the PUSH (Preload) to the edge of Cache, can be achieved with targeted content. PUSH distribution for the main issue to be considered distribution strategy, that is, when distribution of any content. In general, content distribution can be CP (content provider) or CDN administrator manual to determine the content can also be determined by intelligence, the so-called intelligent distribution. It is based on user access to statistical information, and content distribution predefined rules to determine the content distribution process.
PULL is a passive distribution of technology, PULL distribution is usually driven by user requests. When the user requests the contents of the Cache on the edge of the local does not exist (not hit) when, Cache start PULL method from the content source or other CDN nodes in real-time access to content. In PULL mode, the distribution is on-demand content. CDN
in the actual system, the general support of two distribution methods, but by content type and business model of the Bu Tong, the choice is primarily a content delivery modalities will be different. Usually, PUSH way for content access are concentrated, such as a hot spot of the video streaming media content; PULL be more suitable for content access dispersion.
in the content distribution process, for the Cache device, the key is the need to establish the content of the source URL, the content published URL, users access the URL, and content location stored in the Cache mapping between.

for CDN content storage system, the need to consider two aspects of storage problems. One is the content source of storage, one is the content stored in the Cache node.
for the content of the source of storage, due to relatively large size of the content (usually up to several or even dozens of TB), and the throughput of the content, so the, usually mass storage architecture. Such as NAS and SON.
Cache node for the storage, Cache design is a key issue. Factors to be considered include the features and performance are two areas: in function includes a variety of content formats supported, some caching support, including support for capacity performance, multi-file throughput, reliability and stability.
which demands a variety of content formats supported storage system according to the characteristics of different file formats to optimize read and write in order to improve the efficiency of the document to read and write, especially streaming media file read and write.
part of the cache capacity means the flow of media content can be stored and incomplete reading. Part of the cache needs the randomness from the user access to as many users do not completely watch the streaming media programs, in fact, many users access a single stream programs no longer than 10 minutes. Thus, some caches can greatly improve storage capacity utilization, and effectively improve the user request response time. But some of the contents of the cache may cause there to the problem, the need for good design and control.
Cache memory is another important factor is the reliability of storage, currently, most storage systems using RAID technology for reliable storage. However, the use of RAID on different devices in different ways.

content management content management technology in the broad sense, ranging from the release of the contents, injection, distribute, adapt, transfer and a series of processes. Here, the content management point of emphasis after the contents into the Cache content management, we refer to as local content management.
local content management aimed at a CDN node (CDN Cache by the number of devices and equipment constitute a SLB) for. Local content management, content services, the main objective is to improve the efficiency, increase storage utilization of local nodes. Through local content management, CDN node can be aware scheduling to achieve content-based, content-aware scheduling through, did not prevent the user is redirected to the content of the Cache device, thereby enhancing the efficiency of load balancing. Through local content management can be effective in achieving the content in the CDN node shared storage to improve utilization of storage space.
To implement the local content management includes the following aspects.
first local content index. First of all, local content management depends on knowledge of local content. Including the contents of each Cache device name, URL, updated content information. Local content index is based on content-aware scheduling to achieve the key.
two copies of the local content. Usually, in order to improve storage efficiency, the same content in a CDN node stores only one, that is only stored in the Cache on a specific. However, if access to the content service provider over the Cache, it will need in the local (rather than through PUSL way) to achieve content distribution. This can greatly improve efficiency.
Third, local content access state information collection. Cache to gather all the contents of the device to access the various statistics, Cache equipment, service delivery and content available to changing circumstances.
can be seen, through local content management, content management can be the Cache from the original equipment level, up to CDN node level, which greatly increased the CDN scalability and integration capabilities.
In summary, CDN as a support for large-scale high-quality streaming media services, the key technology is now mature and have a wide range of application capabilities.