CDN Technology Detailed Notes

1. Four factors that affect network transmission
(1) "First kilometer": the bandwidth provided by the Web server's link to the Internet.
(2) "Last kilometer": User access bandwidth.
(3) Peering Gateway: interconnection bandwidth between different networks.
(4) long-distance backbone transmission: The first is long-distance transmission delay problem, followed by the backbone network congestion problem

2. The process by which a user accesses a website through a browser is as follows:

① users enter the domain name of the website they want to access in their browser.

The ② browser requests the resolution of the domain name from the local DNS server.

③ The local DNS server if the cache has the parse result of this domain name, the immediate user's resolution request.

④ The local DNS server does not have a cache of parsing results for this domain name, recursively requests resolution to the entire DNS system, and then responds to the browser with the result.

The ⑤ browser obtains the domain name resolution result, is the domain name corresponding service device IP address.

The ⑥ browser requests content from the server.

The ⑦ server transmits the user request content to the browser.

3. The access process after the introduction of DNS

① when the user clicks on the content URL on the site page, after the local DNS system resolves, DNS will eventually give the domain name resolution to the CDN dedicated DNS server that the CNAME points to.

The ②CDN DNS server returns the global Load Balancer device IP address of the CDN to the user.

The ③ user initiates a content URL access request to the CDN's global load balancer device.

④CDN the global Load balancer device selects a zone load balancer device for a user's zone based on the user's IP address and the content URL requested by the user, telling the user to initiate a request to the device.

The ⑤ Zone load Balancing device provides services for the user to select a suitable cache server. The choice of the basis includes: According to the user's IP address, determine which server is closest to the user, according to the URL of the user request to carry the content name, determine which server has the user needs, query the current load situation of each server, determine which server is still capable of service. Based on the comprehensive analysis of these conditions, the zone load balancing device returns the IP address of a cache server to the global load balancer device.

⑥ the global Load Balancer device returns the IP address to the user.

⑦ the user initiates a request to the cache server, the cache server responds to the user request and transmits the user's required content to the user terminal. If the cache server does not have the content that the user wants, and the zone load balancer device still assigns it to the user, the server requests content to its top-level cache server until the source server that traces the Web site pulls the content locally.

System Architecture for 4.CDN

5.CDN Deployment Architecture

In one node, the cache device and the local load balancer device are connected in two ways: one is by-pass, and the other is through.

6.CDN System Classification

(1) Classification based on different content bearer types

• Web acceleration
• Streaming media acceleration
• File Transfer acceleration
• Application protocol Acceleration: Optimized for transport protocols such as TCP/IP.

(2) Classification based on content generation mechanism

The mainstream web site system can be logically divided into three levels, the presentation layer, the business logic layer, the data access layer.

The CDN is divided into two categories: presentation-level replication (static site) and full-site replication (dynamic site), based on the different levels of web transfer done by the CDN.

7.CDN System three-dimensional model diagram

The x-axis is a vertical system that runs through the head-to-end of the system, and each business capability can have its own center, region, and edge-level equipment, with its own independent management system, load balancing system, and distribution service system.
Therefore, in the x-axis direction, each CDN service capability can be a set of relatively independent subsystems.

The classification of y-axis direction is based on the requirements of CDN cascade Cache, hierarchical scheduling and grading service.
CDN management functions, scheduling functions, caching functions, service functions are tiered deployment, different levels of the same functional entities with each other.
From the control function, often the next level control entity is the executor of the control entity at the upper level;
From the caching function, the upper level cache is the content provider of the next level cache entity;
From a service function perspective, the upper level service entity is the capacity complement and backup of the next level of service entity.

In the direction of z-axis, management mainly completes CDN network management and business logic processing.
Network Management provides IP network level configuration management, fault management, network performance management and network security management, is responsible for the entire CDN system network and equipment resources abstraction, extraction of its business capabilities, to provide to the upper business platform.
Business logic processing refers to the CDN system to assist its service platform to complete the implementation of some of the application layer functions, complete and other systems interface adaptation, responsible for the system certification, billing, statistical analysis, System management, user management, SP management and other functions.
The control plane is responsible for managing the content distribution of the whole CDN network, controlling the content distribution and access routing policy, which is the control point of the content data flow of the whole content distribution system.
The data plane undertakes the actual content distribution work, according to the z axis direction and the x axis, the y axis intersection point the specific request, the data plane equipment has the different application service ability.

Reference: "CDN Technical Details" pp.1-29

CDN Technology Detailed Notes