1. What is CDN?
CDN means Content Delivery Network, a distributed network on the internet
It uses advanced intelligent route technology of the content to direct the user¡¯s request during web access to the nearest one to the user of the cache servers around the world for direct access in automatic mode, thus it can increase the response speed and service accessibility for the user at the same time; it as well increased the server loading capacity and the security of the website operation, resulting in improvement of the quality of internet service ultimately.
In 1998, a study group in MIT first put forward the CDN concept when handling the internet access quality. At present, CDN service provided by the professional CDN operational company has been the key means to guarantee access quality.

2. What is the main difference between CDN service and conventional mirror?
CDN is completeness transparent to the user, needless of user manual selection the mirror site for access.
CDN executes inspection of the robusticity of the nodes, so does not the mirror, therefore, CDN is of higher usability;
The content synchronization mechanism of CDN needs no manual intervention, whereas the mirror site requires a complicated system to realize;
The mirror site system is quite complicated, demanding more maintenance work and exerting heavy pressure to the operational maintenance;
CDN deployment is quite convenient, hardly needing any modification to the original site; it can be put in use in very short time and brings about notable effect once it is used;
CDN nodes are widely distributed; while the mirror site can hardly comes up with the same coverage.

3. What is the effect of CDN service to the website?
It increased the access speed, allowing for high-quality service of the website to the user
It reduced the pressure to the website server and bandwidth
It increased the security of the website service
It can easily cope with the shock of abrupt access quantity of different kinds
It sustains the continuity of the website service

4. How to realize cache for quasi-static content?
For quasi=static content, cache is realized in such way that database enquiry program like JSP/PHP to generate page, but the same URL will show the same content for different users. In this situation, Cache can save temporarily (namely cache) the URL and relevant content like the way for a standard URL, even it is ended with an interrogation (?) regardless of the multiple enquiry limits therein. As to this kind of content, the most necessary consideration is the refresh time. For frequently refreshed content, we set the time to 10min or shorter, for less frequently refreshed content, we can elongate the refresh time. Refresh time setting can be executed by folder, or according to the specific URL, or any key field, but it is very flexible any way.
When CDN is used upon quasi-static content, it has great effect in the aspects of significant reducing of the data pressure and increasing of the page response speed.

5.In which areas does Dnion has provided CDN service?
Up to July 2006, Dnion has established up to 42 nodes in the country, which cover all the major domestic telecommunication provider, including China Network Communication, China Telecommunication, China Unicom, China Mobile, China Tietong and Chian Edunet.

6. How can we summarize the actual situation of user access after CDN service is used?
When you has used Dnion CDN service, our operation support system will provide detailed statistical access data to the user, who can use the customer service entrance on the website of Dnion Technology to query the PageView statistical data, Object access statistical data, bandwidth use data and so on. We also provide download of the summary of the access log on all nodes for individual customer, who then can make further statistics and analysis.

7. How can we test if we have used Dnion CDN service?

If you have agreed to test the CDN, our special customer service personnel will contact you to confirm the test channel, specific acceleration item and tactic, while the source serve will hardly need any modification, but it is done through our the configuration at our side. What the customer should do is transfer the domain name resolution right to Dnion Technology and cooperate with us to determine the content to be accelerated. The test will not affect the normal service of the website, any switching is smooth transition, you needn¡¯t to worry about any problem like service interruption. Details about the configuration and operation will be provided via special document before the test.

8. How the security is guaranteed when the DNS resolution right is transferred to Dnion Technology?

Dnion Technology will perform all the related configuration work before switching of domain name and then the test is strictly executed, ensuring the user access will not be affected in any way after the switching took effect. Dnion Technology adopts professional domain name resolution system, which features outstanding reliability and stability; in addition, backup redundant configuration is incorporated in Dnion Technology. Data synchronization is maintained between the primary and backup domain name server, which the data are also distributed on the network from different operational company in different cities; incase of any failure, the backup system will be used to provide service continuously.

9. Why I still feel it is slow when I visit my website at the first time?
Because DNS load balancing technology is used, it will take some time that a series of intricate DNS query is conducted so as to position the geographically near CDN node when you visit the website. After that, the course of website browning will get quicker any way.

10. What is required to be modified in the source website by the CDN service?
One of the major characteristics of CDN service is that it is easy to use, so the source website hardly needs any modification before taking use of CDN service. The principle of CDN is to distribute the content that is suitable for acceleration to the CDN nodes, so the user can access the required content from the near side. Whereas, such distribution is normal access request from the point of the source website, and the content cache and the response of CDN nodes to the user access are all realized by the CDN system. When dynamic application such as database query or user authentication is involved, CDN system will automatically transfer the request to the source site to process, therefore, no modification is required to the source website. If the source website has any monitoring measurement to the access quality to the site, which mostly is realized by simulation of user access, it access response speed and quality will be greatly promoted after CDN service is used.

11. What can I do if I want to stop the CDN service?
If you want to cancel the CDN service, you can use the original directed resolution of source website by screening the CNAME record, and restore the domain name resolution directly.

12. How to ensure the update and Synchronization of the content after CDN service is put in use?
In CDN service, the synchronization of the content in the nodes with the content of the source mainly depends on the refresh time tactic setting. We can set different refresh time for different content. For less-frequently refreshed content, we set longer refresh time so as to alleviate the access pressure to the source website; for frequently refreshed content, we can set the refresh time to 10min or shorter so as to ensure the synchronization of the content. Refresh time setting can be executed by folder, or according to the specific URL, or any key field, but it is very flexible any way.

13. What content are suitable for acceleration by CDN technology?
In addition to the static webpage and pictures that are very suitable for acceleration by CDN technology, many other dynamically-generated web pages are also suitable for it. This content mainly is the pages generated by database enquiry program like JSP/PHP, but the same URL will show the same content for different users. In this situation, Cache can save temporarily (namely cache) the URL and relevant content like the way for a standard URL; even it is ended with an interrogation (?), Regardless of the multiple enquiry limits therein. Such quasi-static content in the website will has the same visible effect after CDN acceleration.