What is a CDN?
The full name of CDN is content Delivery network, that is, contents distribution network. The goal is to add a new layer of network architecture to the existing Internet, publish the content of the Web site to the nearest user's network "edge", so that users can get the required content nearby, improve the user's response speed to visit the site.
CDN is different from mirroring because it is smarter than mirroring, or it can be likened to a more intelligent image + cache + Flow diversion. cdn= Therefore, CDN can obviously improve the efficiency of information flow in Internet network. From the technical comprehensive solution because of the network bandwidth is small, the user accesses the quantity to be big, the dot distribution unequal problem, enhances the user to visit the website the response speed.
To better understand the CDN, let's look at the workflow of the Cdn. When a user accesses a Web site that has already joined CDN Services, it first determines the best CDN node of the nearest user through DNS redirection technology, and points the user's request to the node. When the user's request arrives at the specified node, the CDN server (the cache on the node) is responsible for providing the user with the content requested by the users. The specific process is: users in their own browser to enter the site to visit the domain name, browser to the local DNS request resolution of the domain name, local DNS will send requests to the site's primary DNS, the primary DNS based on a series of policies to determine the most appropriate CDN node at that time, and the resolution of the results (IP address) to the user, The user requests the content of the corresponding Web site to the given CDN node.
What is a double line?
The better dual-line access is not required to use two IP addresses.
Full-network routing or dual-line access is a link layer technique for network access. Refers to the server in the data Center computer room at the same time with netcom and telecommunications, such as a variety of network exports, the upper layer of the computer room switch set up a full network routing technology, so that each time the server to the external network can automatically be assigned to the fastest link. Thus realizes the telecommunication and the Netcom user all may simultaneously the high speed access.
However, this technology can be used to solve the problem of the interconnection of data output, but the connection from your computer terminal to the server is usually unable to select the link mode automatically, so the speed you upload data will still be affected by the network interconnection problem. But usually we only need a very small amount of upload, but most of the Web content is provided to the viewer to download.
In addition to full network routing (dual-line access), CDN technology can also achieve fast access to each network. But in addition to the CDN technology will encounter upload slow, the more troublesome is the content cache and synchronization cycle limit, is your content can not be released in time, the user is always browsing to the relative lag of information.
Therefore, dual-line access has become the current Web site to solve the problem of interoperability of the best solution.
Dual-line room is a unique product in such a special network environment, dual-line room can only solve the problem of Netcom and telecom access to the bottle well, the network transmission of the link problem and other ISP interoperability problems are not resolved.
CDN is the principle of edge access, visitors to the nearest data, which greatly shorten the visitor to the source site between the transmission distance. All ISP Interoperability and network link problems can be resolved.
The advantages of dual-wire room trusteeship:
Solve the access bottle well of Netcom and telecom
No data synchronization issues
The disadvantage of dual-wire room trusteeship:
At present, the dual-line room in the market has a severe bandwidth limit
Prices are much more expensive than regular hosting.
Need to do intelligent parsing
Servers need to move
For the strength of the enterprise can build their own dual-line room, but the investment is too large, and the implementation of more complex, more difficult, than the choice of Cdn.
The advantages of CDN
Simple maintenance, automatic synchronization of website data
Resolves all ISP interoperability issues, and network link issues
Reduce the pressure on the source server
Effective anti-DDoS attacks
Save the Backbone network resources
The drawback of CDN
Implementation of complex
At present, most of the CDN is only for static content acceleration, the dynamic acceleration effect is not good, and the effect of the two-line dynamic acceleration is the same as static.
CDN and two-wire room difference Summary:
CDN's cover range is wider, the dual-line room only solves the problem of the speed of the network between Netcom and telecom, and can not solve the problems of one kilometer (from IDC to the network between the Telecommunication Bureau of the user).
CDN as a solution to large web site access speed and quality, as well as to solve the telecommunications and netcom access bottle Well is a good solution, dual-line computer room as a solution between Netcom and telecom access to the bottle well problem is a good choice.
If you do not want to increase any costs, do not change the status of the current situation, the solution to the Netcom and telecom access to the problem of the bottle to join CDN Alliance is the best solution.
Let's talk about two-line, multi-line server rental hosting pattern.
First, railcom (Mobile, Unicom): A lot of friends to host the server in railcom (Mobile, Unicom)
In fact, put the server in railcom is almost to seek telecommunications users and netcom users of the compromise, such as putting the server in telecommunications, telecommunications users to open the site needs 1 seconds, netcom users need 5 seconds, and now put in the CRC, may be telecom and Netcom user access is 3 seconds, This actually involves the average customer is willing to tolerate the waiting time, such as the General People tolerate a website open is 4 seconds, it is a very good solution, so that the telecommunications users and netcom users can tolerate. But for example, if the server is used as a video teaching class, then this approach is not very good, which will make telecommunications and netcom user access speed is slow. In Railcom, the general price is relatively cheap (relatively real dual-line room), if the friends are mainly to do the web, members of the speed is not particularly high, then you choose Railcom is a good plan.
Two-line dual IP hosting
This situation can be divided according to whether or not to have 2 public network exports:
1, with 2 public network exports: This dual-line dual IP hosting effect is better, but relatively high cost of hosting, and bandwidth resources are also more expensive, this room is very scarce resources, currently in the country has 2 public network export dual-line room only one, Because the SARFT behind the telecommunications and netcom to engage in dual-line room, feel this to the telecommunications and Netcom's business is very large, not conducive to the development of telecommunications and Netcom, now the only dual-line network with the public net export room is because 2000 years has been applied for good, not easy to undo, the subsequent application has not approved.
2, do not have their own public network exports: such a custodian is generally from the telecom pull 100M exclusive optical fiber, netcom pull a 100M exclusive fiber, and then buy some IP, which is now almost the most commonly seen on the market, and the general agent technology and equipment is not very clearance, Need to set up double IP through the dual network card, and have the public network export room, equipment and technical force are also good, are through a single NIC binding dual-IP.
In fact, one of the biggest features of this model is the 100M exclusive optical fiber is actually and the operator's switch between the connection is 100M (also can be understood as a metropolitan network 100M alone), rather than the public net export on the 100M alone, It is estimated that the general provincial capital city 100M exclusive optical fiber generally in the public net exports can be divided to about 20M is good, this is based on the city's overall bandwidth resources, if the city's bandwidth resources are very loose, it is possible that such a metropolitan network of 100M alone in the public outlet can also run very high.
3, have a public network to export: In fact, the agent of this model does not have their own small room, he is in the telecommunications rental cabinets to do business, and then in the network hosting a machine, buy a section of IP, do proxy server, this can also help customers set up 2 IP on the server, But in this way through the proxy server to go to the speed of the network resolution is slower, faster access to the Internet, so this effect is not very good, friends in the choice of two lines when try not to choose such a dual-line hosting.
Three, dual-line single IP hosting
1, there is a public network export: Such a custodian is already have such a good resource, such as telecommunications, they this effect is better, and is a single IP implementation, but such resources are very scarce, the general custodian is no way to get such resources, there is the Yu-net in Zhengzhou Jing ' an data center, The use of BGP technology to achieve, but the stability is another disappointment.
2, no public network exports: that is, from the telecommunications and Netcom pull out, behind themselves through the device to set up the road, but also to the user to assign an IP, to achieve the two lines, but temporarily in the market has not seen the effect is very good, famous do good, probably because there is no public net exports, There is a lack of advanced equipment and other reasons.
With this knowledge, let me talk about how to choose:
First of all, let's talk about dual IP hosting.
Zhengzhou Double line room (technical and environmental facilities are good, stability is also very good, but can not put SF, bandwidth allocation is also quite sufficient-each machine bandwidth alone to enjoy 5M, which in the national similar dual-line room in the 59 interconnection provides is to occupy the absolute price-performance)
If it is a single line of custody, it is recommended not to choose Shanghai, although Shanghai's room environment and all aspects are China can be said to be the best room location. But including in Zhangjiang, Waigaoqiao, Wusheng and so on the big room is basically full. Shanghai has dragged too many servers, now in the past to put the server, there is no good bandwidth to you.
Telecommunications, can choose Changchun Chongqing Guangdong, Jiangxi Telecom XI ' an telecom, etc.
Netcom, you can choose Henan Netcom, Zhengzhou Two long netcom, Shanghai Netcom (less bandwidth, high price)
In Beijing this place, the bandwidth is not enough, and the general price is very high, is a good technology, good stability, anti-attack ability is also very strong, there is a better ability to attack the room, the basic is in Zhengzhou, Zhejiang and other place, Shanghai is also good, but not enough bandwidth, firewall is no use ...
Dozen so many words, just hope in search of friends, can have a good choice of plan ... Compare, make a good choice.