IDC must learn--CDN learning

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IDC must learn--CDN learning   A CDN Introduction CDN (often referred to as content distribution network distribution networks, sometimes referred to as content delivery network content delivery networks) As a way to improve the content of the network, the purpose is to publish the content of the website to the "Edge" of the network closest to the user by adding a new layer of network architecture to the existing Internet, so that users can get the content they need, solve the congestion of Internet network, and improve the response speed of users to visit the website. In particular, the technology of improving the service quality of streaming media content transmission and saving backbone network bandwidth has been widely used at home and abroad. A CDN is different from mirroring because it is smarter than mirroring, or it can be used as a metaphor: cdn= more intelligent mirror + cache + traffic diversion.    Thus, CDN can significantly improve the efficiency of information flow in Internet networks. From the technical comprehensive solution due to network bandwidth is small, user access is large, dot distribution is not equal problem, improve the response speed of users to visit the site. To better understand the CDN, let's look at the workflow of the Cdn. When a user accesses a website that has been added to a CDN service, it first determines the best CDN node that is closest to the user by using DNS redirection technology and points the user's request to that node. When a user's request arrives at the specified node, the CDN server (the cache on the node) is responsible for providing the user with the requested content. The specific process is: the user in their own browser to enter the domain name of the site to visit, the browser to the local DNS request for the domain name resolution, local DNS requests to the site's primary DNS, the primary DNS based on a series of policies to determine the most appropriate CDN node, and the results of the resolution (IP address) sent to the user, The user requests the content of the corresponding site to a given CDN node.   The application of CDN business   How to alleviate the network congestion, improve the speed of users to obtain information, has become a major problem that troubles many enterprises and service providers. A CDN is a content distribution network, which can be thought of as a value-added network built on the existing IP network infrastructure (delievery). CDN Technology combines multi-point load balancing, mirroring and cache technology, and uses intelligent allocation technology to assign site content to multiple nodes according to the principle of the nearest visitor, based on the location of the visiting user.   CDN Business Features and advantages   1, local cache acceleration to improve the enterprise site (especially with a large number of images and static page site) access speed, and greatly improve the stability of the above properties of the site 2, the mirror service to eliminate the interconnection between the different operators of the bottleneck caused by the impact, The implementation of cross-operatorNetwork acceleration, to ensure that users in different networks can get good quality of access. 3, Remote acceleration remote access users based on DNS load balancing technology to automatically select the cache server, select the fastest cache server, speed up remote access 4, bandwidth optimization automatically generate the source server remote mirror cache (Mirror cache) Server, Remote user access to read data from the cache server, reduce the bandwidth of remote access, share network traffic, reduce the original site Web server load and other functions. 5, cluster anti-attack widely distributed CDN node plus the intelligent redundancy between nodes, can effectively prevent hacking and reduce the impact of various D.D.O.S attacks on the site, while ensuring a better quality of service.   CDN Business advantages are reflected in the following aspects: Reduce network bandwidth consumption, reduce network access latency and user response time, increase network performance and site content availability, improve the management and control of Web resources, intelligent allocation of routing and traffic management, the content sent is protected, Unauthorized users cannot be modified; Content providers can determine the content of their services locally, content providers improve the quality of their services while reducing costs, and can add new devices linearly and smoothly to protect their original investments.   The working principle of CDN in describing the implementation principle of CDN, let us first look at the traditional non-cached service access process, in order to understand the way CDN cache access and non-cached access to the difference:   by visible, user access to the non-use of CDN cache site process is:  

  1), the user to the browser to provide access to the domain name, 2), the browser calls the domain name resolution function library to resolve the domain name to obtain the corresponding IP address of the domain name, 3), the browser uses the resulting IP address, the domain name of the service host to send data access requests, 4), the browser according to the host The content of the Web page is displayed. With the above four steps, the browser completes the process of receiving the domain name from the user to get the data from the server that corresponds to the domain name. The CDN network is to add the cache layer between the user and the server, how to direct the user's request to the cache to get the data of the source server, mainly by taking over the DNS implementation, let's look at the process of accessing the website using CDN cache:       Pass, We can understand that the use of the CDN cache after the site's access process changed to: 1), the user to the browser to provide access to the domain name, 2), the browser calls the domain name resolution library to resolve the domain name, because the CDN to the domain name resolution process has been adjusted, So the analytic function library generally get the CNAME record of the domain name, in order to get the actual IP address, the browser needs to parse the acquired CNAME domain name again to obtain the actual IP address, in this process, the use of global load balancing DNS resolution, such as based on geo-location information to resolve the corresponding IP address , allowing users to access them nearby. 3), this resolution obtains the CDN cache server IP address, the browser obtains the actual IP address, sends the access request to the cache server, 4), the cache server according to the browser provides the domain name to access, through the cache internal private DNS resolution obtains this domain name the actual IP address, Then by the cache server to the actual IP address to submit access requests, 5), the cache server from the actual IP address to obtain the content, on the one hand in the local storage for later use, two aspects of the data obtained to the client to complete the data service process; 6), The client obtains the data that is returned by the cache server and completes the entire browse data request process. Through the above analysis, we can obtain, in order to achieve both transparent to the ordinary user (that is, the user client does not need to make any settings after adding the cache, directly use the original domain name of the accelerator site can be accessed), but also to provide accelerated services for the designated site while reducing the impact on the ICP, Simply modify the domain name resolution portion of the entire access process to achieve transparent acceleration services.   Five key technologies of CDN   CDN Key technologies include content routing technology, content distribution technology, content storage technology, content management technology and so on.   1. Content Routing Technology CDN load Balancing system realizes CDN's content routing function. Its role is to direct the user's request to the entireThe best nodes in a CDN network. The best node selection can be based on a variety of strategies, such as the closest distance, the lightest node load, and so on. Load balancing system is the core of the whole CDN, and the accuracy and efficiency of load balancing directly determine the efficiency and performance of the whole CDN. Typically, load balancing can be divided into two tiers: Global load Balancing (GSLB) and local load balancing (SLB). The primary purpose of global load balancing (GSLB) is to direct the user's requests to the nearest node (or region) across the network. Therefore, proximity judgment is the main function of global load balancing. Local load balancing is generally limited to a certain area of the region, the goal is to find a specific area of the most suitable node to provide services, so the health of the CDN node, the load situation, the supported media format and other operational states are the main basis for local load balancing decision. Load Balancing can be implemented in several ways, including DNS, application layer redirection, Transport layer redirection, and so on. For global load balancing, there are usually two ways to perform a proximity decision, a static configuration, such as a mapping of IP addresses to CDN nodes based on a static IP address configuration table. Another way is dynamic detection, such as real-time to let the CDN node detect the target IP distance (can use Rrt,hops as a unit of measurement), and then compare the detection results for load balancing. Of course, static and dynamic methods can also be used in combination. For local load balancing, in order to make effective decisions, you need to get the running state of the cache device in real time. There are generally two methods of obtaining, one is active probing and the other is protocol interaction. Active detection for the SLB device and the cache device does not have a protocol interface, the Ping and other commands to initiate detection, based on the results of the return analysis status. The other is protocol interaction, in which the SLB and cache Exchange run state information in real-time based on a pre-defined protocol for load balancing. In comparison, the protocol interaction than the detection method to be accurate and reliable, but there is no standard protocol, the implementation of the manufacturers are generally only private agreements, interoperability is more difficult.   2. Content distribution Technology content distribution contains the process of caching from the content source to the edge of the CDN. From the implementation perspective, there are two main content distribution technology Ush and pull. Push is a technology that is actively distributed. Typically, push is initiated by the Content management system to distribute content from the source or central media repository to the cache nodes at each edge. The distribution of the agreement can be adopted http/ftp and so on. Content that is distributed through push is generally a hot-spot content that can be delivered through push-mode pre-distribution (preload) to the edge cache for targeted content. The main issue to consider for push distribution is the distribution strategy, that is, when to distribute what content. In general, content distribution can be provided by the CP (contentVendor) or CDN Content Manager, can also be determined intelligently, the so-called intelligent distribution. It determines the process of content distribution based on user-accessed statistics, as well as rules for predefined content distribution. Pull is a passive distribution technique, which is typically driven by a user request. When a user requests a content that does not exist (misses) on the local edge cache, the cache initiates the pull method to get the content in real time from the content source or other CDN node. In pull mode, the distribution of content is on-demand. In a real CDN system, both distributions are generally supported, but depending on the type of content and the business model, the primary content distribution method is selected differently. In general, push is suitable for content access comparison, such as hot video streaming content ull way more suitable for the situation of content access scattered. In the process of content distribution, the key to the cache device is the need to establish a content source URL, a URL for the content publication, a URL that the user accesses, and a mapping between where the content is stored in the cache.   3. Content storage technology for CDN Systems, two aspects of content storage issues need to be considered. One is the storage of the content source, and the other is the storage of the content in the cache node. For storage of content sources, because of the large size of content (typically several or even dozens of TB), and the high content throughput, a mass storage architecture is often used. such as Nas and son. For storage in the cache node, is a key issue for the cache design. Factors to consider include features and performance in two areas: features include support for a variety of content formats, support for partial caches, performance including supported capacity, multi-file throughput, reliability, and stability. Among them, the support of various content formats requires the storage system to optimize the reading and writing characteristics of different file formats to improve the efficiency of file content reading and writing, especially the reading and writing of streaming media files. Partial caching means that streaming media content can be stored and read in an incomplete manner. The demand for partial caching comes from the randomness of user access behavior, as many users do not fully watch the entire streaming program, and in fact, many users visit a single streaming program for less than 10 minutes. Therefore, the partial caching capability can greatly improve the utilization of storage space and effectively increase the response time of user requests. However, partial caching can lead to fragmentation of content and requires good design and control. Another important factor in cache storage is the reliability of storage, where most storage systems are now reliably stored using RAID technology. However, different devices use different raid modes.   4. Content management technology content management in a broad sense, from the content of the release, injection, distribution, adjustment, transmission and a series of processes. Here, Content management highlights the contentContent management after entering the cache point, which we call local content management. Local content management is primarily for a CDN node (consisting of multiple CDN cache devices and a SLB device). The primary goal of local content management is to improve the efficiency of content services and improve the storage utilization of local nodes. With local content management, content-aware scheduling can be implemented in CDN nodes, and content-aware scheduling can avoid redirecting users to cache devices without the content, thereby increasing the efficiency of load balancing. Local content management can also effectively realize the storage sharing of CDN node content and improve the utilization of storage space. On the implementation, the local content management mainly includes the following aspects. One is the local content index. Local content management relies first on the knowledge of local content. Includes the name of the content on each cache device, URL, update time, content information, and so on. Local content indexing is the key to implementing content-aware scheduling. The second is the local content copy. In general, to improve storage efficiency, the same content is stored only in one CDN node, which is stored only on a specific cache. However, once access to the content exceeds the cache's service delivery capabilities, content distribution needs to be implemented locally rather than through PUSL. This can greatly improve efficiency. The third is the local content access state information collection. Collect statistics on each content access on each cache device, and the availability and content changes of the cache device. It can be seen that through local content management, content management can be increased from the original cache device level to the CDN node level, which greatly increases the CDN scalability and comprehensive capabilities.   To sum up, as a key technology to support large-scale high-quality streaming media services, CDN has been basically mature and has a wide range of application capabilities.   Six, the main three subsystems of the CDN network   1. 3DNS is the key subsystem in CDN service. When a user accesses a website that joins a CDN service, the domain name resolution request will eventually be given to 3DNS for processing. 3DNS provides a user with a predefined set of policies that will provide users with the most immediate access to the user's nodes, enabling them to get a quick service. At the same time, it maintains communication with all CDNC nodes distributed around the world, collects the communication status of each node, and ensures that the user's request is not assigned to an unusable CDN node. 2. CDN node for ordinary Internet users, each CDN node is the equivalent of a web that is placed around it. With 3DNS control, the user's request is transparently directed to the node closest to him, and the CDN server in the node responds to the user's request as if it were the site's original server. Because it is closer to the user, the response time must be faster. Each CDN node consists of two parts: the loadEqualization device and Content Acceleration Server load balancer is responsible for the load balancing of each cache in each node to ensure the efficiency of the node, while the load balancing device is responsible for collecting the information of the nodes and the surrounding environment, maintaining the communication with 3DNS, and realizing the load balance of the whole system. The Content Acceleration Server (Cache) is responsible for storing a large amount of information about a customer's website, responding to a local user's access request as if it were a Web server close to the user. 3 CDN Management System is the guarantee that the whole system can operate normally. It can not only monitor the subsystems and equipment in real time, but also produce corresponding alarms for various faults, and can monitor the total traffic and the traffic of each node in real-time, and keep in the database of the system, so that the network manager can make further analysis conveniently. Through the perfect network management system, the user can modify the system configuration.   Seven, CDN products at present, the introduction of more mature CDN products manufacturers have Cisco, F5 and interconnection companies, the former two Cdn is based on hardware systems, and the latter CDN is a software-based universal platform, a good combination of line and service advantages. The following is a simple analysis of the connected Cdn--smart CDN. Interconnect uses a combination of overall load balancing (GSLB), caching technology (cache), and mirroring Technology (MIRROR) to provide customers with remote network acceleration services. The specific plan is to use the Connected Network acceleration service in the centralized city and region of users outside the main site of the website, and the interconnected intelligent GSLB System will guide the website users to access the "best" Cache/mirror server through the interconnection network, thus bypassing the Internet congestion link and alleviating the load of the primary site server. Realize the network acceleration, and solve the simple cache/mirror can not solve the problem. Smart CDN works through DNS resolution or HTTP redirection to complete the delivery and synchronization of content through the cache server or a mirrored site offsite. DNS method The accuracy rate of user location judgment is greater than 85%,http method accuracy is more than 99%. The actual calculation, the user access to the cache server group of data volume and cache server to the original site to fetch content of the amount of data between 2:1 to 3:1, that is, to share the 50%~70% to the original site repeatedly accessed data volume (mainly pictures, streaming files and other content). For mirroring, the rest of the traffic, except for data synchronization, is done locally and does not have access to the original server. Smart CDN System based on the actual user access to the IP address to determine the user location, direct user access to the fastest response to the site. The whole system management is simple, the user can determine what content needs to do distributed distribution through GUI, the system will complete the whole process of copying, updating and synchronizing the database automatically. Moreover, the system has the ability of self-diagnosis and load balancing, and any link occursNot affect the accessibility of the entire system.   VIII. CDN Applications and customers current CDN services are mainly used in securities, financial insurance, ISPs, ICP, online transactions, portals, large and medium-sized companies, network teaching and other fields. In addition, in the industry special network, the Internet can be used, and even network optimization of LAN. Using CDN, these sites do not need to invest in expensive various kinds of servers, set up sub-sites, especially the wide application of streaming media information, long-distance teaching courseware, such as the use of more bandwidth-intensive media information, the application of CDN Network, the content to the edge of the network, so that the content demand point and delivery point to minimize the distance between Therefore, it is of great significance to improve the performance of Web site. CDN Network Construction mainly has the Enterprise Construction CDN Network, serves for the enterprise, the IDC CDN Network, mainly serves the IDC and the value-added service, the network operation main constructs the CDN network, mainly provides the content pushes the service, the CDN Network service provider, specially constructs the CDN to do the service, The user cooperates with the CDN organization, the CDN is responsible for the information transmission work, guarantees the information normal transmission, maintains the transmission network, but the website only needs the content maintenance, no longer need to consider the traffic question. CDN can guarantee the fast, safe, stable and extensible network. IDC set up a CDN network, IDC operators generally need to have a number of IDC centers around the division, the service object is hosted in the IDC center of customers, the use of existing network resources, less investment, easy to build. For example, an IDC has 10 rooms in the country, joined the IDC CDN Network, hosted on a node of the Web server, equivalent to 10 mirror servers, the nearest customer access. Broadband metropolitan Area Network, the speed of the Internet, the city bandwidth will generally be the bottleneck, in order to reflect the high-speed experience of the metropolitan Area Network, the solution is to cache the Internet content to the local, the cache will be deployed in the metropolitan area of the pop points, so as to form an efficient and orderly network, Users can access most of the content in just one jump, which is an app that accelerates all CDN applications.   Nine streaming media and CDN hosting technology     Abstract: This paper starts with the development analysis of Internet service driven by broadband access, puts forward the development trend of broadband multimedia technology and business, and then analyzes the streaming media technology and business characteristics which can be operated at present, The demand for CDN carrier technology is also deduced. Keywords: multimedia streaming CDN

1. Broadband access drives the development of Internet services as a new information flow bearer platform, the Internet is profoundly changing the way people communicate and think. In recent years, China's number of Internet users is growing rapidly, according to the China Internet Information Center (CNNIC) Statistics report, as of December 31, 2003, the total number of Internet users in China is 79.5 million people. The number of broadband Internet users reached 17.4 million, an increase of 7.6 million people in six months, a growth rate of 77.6%, compared with the same period last year 163.6%. Among the four ways of Internet users, broadband users are growing fastest. From CNNIC statistics can be seen, at present, China's Internet broadband access business is in a high-speed development stage. When the broadband network and broadband access problems are basically solved, the business becomes the key. At present, China's Internet broadband access and application business is in a benign interaction of the high-speed development stage, broadband Internet has gradually become the urban areas of consumer fashion, the increasing number of broadband users also directly lead to more SP/CP engaged in the operation of broadband content, Internet broadband content and application of colorful. From the broadband start, the value of the Internet is beyond the provision of pure IP connectivity, browse static Web pages and text-based e-mail exchange, really become people's life and work, enterprise operation must be through the way. According to CNNIC's survey, Leisure Entertainment has become the second major goal after acquiring information, and its proportion is increasing. Survey 1-Details please refer to "China Multimedia video" phase Nineth. It is clear that developing dynamic, interactive, rich media content and value-added applications is an important means of attracting users. The network industry based on broadband is fundamentally different from the traditional narrow-band internet industry, which has a very different application prospect and operation model: Broadband is facing commercial applications, entertainment, consumer and home services, it needs a rich and varied content-based.

2, to create broadband multimedia applications is the key broadband multimedia services to take full advantage of the advantages of high bandwidth and interactivity, to provide a variety of users to meet the effective needs of value-added services, so that users feel broadband fees value for money. Mature Broadband multimedia services should have at least the following four features: (1) Multimedia: Broadband services should take full advantage of the characteristics of high bandwidth, the use of images, sound and animation and other narrowband networks can not provide a variety of media means to provide users with a variety of content. (2) Interactivity: With the increase of bandwidth, restricting the interaction of the bottleneck will be basically eliminated, the interaction as the core of the various services will also become the mainstream of internet services. The broadband service only has the interactivity, only then can mobilize the user to consume the enthusiasm. (3) Humanization: The maturity of network technology, the accumulation of network service experience, plus the increase of bandwidth, provides the conditions for the network humanized service. With the digital home, multimedia virtual city and community as the basic service space, the humanized interaction as the basic service form of broadband network services is gradually formed. (4) Personalization: Broadband business should be personalized service. corresponding to different customer groups, such as different industries, different ages, users can freely choose and customize the specific broadband value-added services according to their consumption habits and actual usage situation. By satisfying the above characteristics of the business derivative of the wide range of broadband value-added applications, such as remote video conferencing, VOD video-on-demand, network TV, distance learning, telemedicine, interactive network games, digital home, etc., there are other like Digital library, Multimedia mall, digital guide and so on, The business opportunities contained therein are likely to be beyond our estimation now. Broadband multimedia applications need to create a sound industrial value chain environment, this chain involves a number of industrial entities, each application involved in different industrial entities, even the same industry entity, the focus of various applications will be different. In the case of video communication business, the members of the industry value chain may include: Network providers, video equipment providers, video service providers, industry application providers, video value-added service providers, video users, and so on, in the chain, operators usually appear as network providers and video service providers. Broadband multimedia business products to succeed in gaining market recognition, it is necessary to have a good business operation model if all the parties concerned have the opportunity to gain or obtain service. In line with the rules of the market, all parties are willing to accept the operation mode is the broadband business to smooth development of the key factors, should be given sufficient attention.

3, streaming media is an important branch of broadband multimedia can be said, streaming media technology and business is a major branch of broadband multimedia technology and business. Streaming media refers to the continuous audio/visual data stream that is transmitted and played strictly in chronological order in internet/intranet. Streaming media has three features: continuity (continuous), real-time (real-time), sequential (time-ordered), which has a strict pre-and post-sequence relationship. Unlike the traditional multimedia file after downloading, the streaming media does not download the whole file before playing, and the streaming media stream will be broadcast anytime after the content is cached. Stream transmission can be divided into two kinds, one is sequential streaming (progressive streaming), one is real-time streaming (real-time streaming). Sequential streaming is a sequential download in which the user can watch the online media at the same time, and at a given moment, the user can only watch the part that has been downloaded, and not jump to the front part that has not yet been downloaded. Sequential streaming is unlike real-time streaming, which can be adjusted at the speed of a user's connection during transmission. Because the standard HTTP server can send this form of file and does not require other special protocols, it is often referred to as an HTTP streaming. Real-time streaming means ensuring that the media signal bandwidth matches the network connection so that the media can be viewed in real time. Unlike HTTP streaming, live streaming requires a dedicated streaming media server and transport protocol. Real-time streaming is always delivered in real time, especially for live events and random access, enabling users to fast-forward or rewind to view front or back content. Sequential streaming is relatively simple, closer to the traditional download viewing mode, its adaptability is poor, also can not support the interaction, its application scope is limited, but because of its low latency requirements, so it can support high-quality streaming media data transmission. The real-time streaming media has more flexible function, and the adaptability of the network is also strong, it needs the specialized streaming media server, the related control protocol, needs the more stable network transmission condition. Current streaming media technology is mainly focused on providing support for this kind of real-time stream transmission. The implementation of real-time streaming requires an appropriate transport protocol. In general, real-time data is not transmitted by TCP, because TCP's per-packet acknowledgement mechanism requires more overhead, and TCP window-based congestion control technology does not support stable rate streaming. Second, TCP is more sensitive to packet loss, and its retransmission mechanism is not necessary for real-time streaming. So in the implementation of real-time streaming transmission, HTTP/TCP is generally used to transmit control information, and RTP/UDP is used to transmit real-time data information. Streaming media technology can be widely used in multimedia news publishing, online broadcast, network advertising, e-commerce, video-on-demand, distance education, telemedicine, network radio, real-time video conferencing, and so on, it enriches the traditional content of the Internet expression, givingBroadband applications are more entertaining and interactive. Streaming media technology will become the mainstream technology of the future broadband network business. Real-time and quality are the key issues in streaming media. In order to guarantee the delay and quality, the network must provide sufficient bandwidth resources, and the guarantee of resources depends on many other control, such as traffic control, congestion control, etc. When the network resources change, must also be able to adapt to this change and make corresponding adjustments. In addition, effective audio and video coding can not only reduce the amount of data transmitted, but also can effectively reduce the quality degradation due to data loss (combined with certain Transmission Control Protocol), therefore, encoding is also an important technology to ensure the quality of streaming media applications.

4, the transmission of streaming media needs CDN support to video-on-demand and other film and television program-based streaming media services to bring a great impact on network operations, the traditional network model and business model is difficult to meet the needs of streaming media business. From the above discussion, we can conclude that the properties of streaming media business are mainly embodied in the following aspects: (1) high bandwidth demand. General film and television program bandwidth needs to be up to 500kbit/s~1mbit/s, and requires a stable bandwidth guarantee. (2) High QoS guarantee requirements. The streaming media service has strict requirements on QoS, such as 750kbit/s mms/tcp Media stream requires end-to-end packet loss rate of less than 2%, bidirectional delay 140ms. (3) Bidirectional asymmetric/symmetric flow requirements. For video-on-demand programs, it is generally a two-way asymmetric service. (4) Point-to-multipoint broadcast streaming requirements. For IPTV, live broadcast business, it is necessary to support stream transmission from single point (broadcast source) to multiple receiving point (user terminal). (5) Concurrent service/Business number is a bottleneck. Is streaming media business generally a server? Client or client? The client's business service architecture, AV codec is one of the important functions of the server and client, depending on the audio codec needs to consume a lot of server/client software and hardware resources, so the current server or client is difficult to withstand large concurrent service/business requests, A generic server can only support concurrent media stream access within 1000. It is because the streaming media business has the above attributes, and the current packet-based IP network is not designed for the above-mentioned business attributes, so directly on the current IP network hosting with the above attributes of the streaming media business will produce the following problems: (1) End-to-end bandwidth and QoS is difficult to guarantee. (2) The network usually does not support multicast, broadcast business needs to adopt multiple point-to-point transmission, not only consumes a large number of backbone network bandwidth, but also a great pressure on the source point. (3) Once the streaming media service users and the volume of business increased, the flow of the existing network traffic model caused a great impact, and even make the existing network difficult to meet the normal business development. (4) SP Access is a bottleneck that will affect the ongoing business, access bandwidth, business access capability description. The above problems are difficult to solve under the existing network framework, and the introduction of content distribution Network (CDN) is to solve these problems. The advantages are: (1) through the introduction of the CDN, the User Service point can be closer to the user, can be placed in the provincial network, local network, or even in the community, can be currently unresolved bandwidth guarantee and QoS guarantee problem distance shortened, thus can effectively "solve" this problem. (2) Through the introduction of CDN, a large number of streaming media content can be pre-distributed to the provincial network, local network scope, but also through the local automatic cache operation, greatly alleviate the streaming media business to the backbone of the impact of traffic flow. (3) Through the introduction of CDN, we can realize the tree distribution and service of broadcast stream, and realize "application layer" multicast. (4) PassThrough the introduction of CDN, the streaming media service server decentralized and decentralized, can effectively alleviate the pressure on SP access. Detailed consultation plus QQ1181180295

IDC must learn--CDN learning

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