At present, edge access of CDN on IPTV network is an effective way to improve QoS of IP bearer network. Many operators deploy CDN/MDN on broadband network, which lays a good foundation for the construction of IPTV network. The emergence of the CDN network has maximized the use of Internet resources. It will greatly promote the development of domestic IPTV services.
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1. Production of CDN technology
At present, the number of users accessing the Internet is increasing; the number of Web sites continues to increase; the resources available for access are becoming more and more abundant, especially texts, images, music, advertisements, streaming media, animations, etc.; Incremental, resulting in a large demand for network bandwidth, and network access delays and waits are always ubiquitous, which lead to network congestion, server overload, online application waiting time is too long, etc., making the entire Internet content transmission performance decline .
How to alleviate network congestion and improve the speed at which users can obtain information. It has become a big problem that has plagued many companies and service providers. Relying on increasing bandwidth to solve this problem is one aspect. In addition, it is also affected by factors such as route blocking and delay during transmission, and the processing power of the web server. These are closely related to the distance between the visitor and the web server. Therefore, even if each ISP increases the network bandwidth, if the distance between the visitor and the website is far, the communication between them needs to be heavily routed and processed, and network delay is inevitable. The requirements of the network system are getting higher and higher (such as the response time of the access, the content of the website and the reliability of the service provided), so the CDN (Content Delivery Network) technology came into being.
In 1996, a team from the Massachusetts Institute of Technology proposed the concept of CDN and began research on CDN technology. In 1999, they established a professional CDN service company to provide professional services for Yahoo. Nowadays, many enterprises and service providers have begun to use the content delivery network CDN technology to improve the quality of network services to meet the needs of users.
2, the definition of CDN
The full name of the CDN is the Content Delievery Network, the content delivery network. The CDN is a value-added network built on the existing IP network infrastructure. It is a layer of network architecture deployed at the application layer.
Vendors that offer CDN technology products have their own solutions, and CDN operators have different implementations, but the functions implemented by CDN technology are the same. That is to combine multi-point load balancing, routing or caching technology, using intelligent allocation technology, the content is distributed to multiple nodes according to the principle of the nearest access according to the location of the visiting user.
In the traditional IP network, the user requests directly to the original server based on the network address, and the CDN service provides a service layer, supplements and extends the Internet network, and promotes frequently accessed content to the user as much as possible, providing processing based content. New capabilities for traffic forwarding to route routes to the best server. Dynamically get the content you need. It changes the way it distributes information to users, from passive content recovery to active content forwarding.
The core of the CDN is edge access and transparent access. It used to be used for Web access acceleration and only supports the HTTP/FTP protocol. In 2003 and 2004, the emergence of domestic streaming media services, CDN began to support protocols such as MMS/RTSP, CDN has been greatly developed, sometimes called MDN (Media Delievery Network).
3. Features and advantages of CDN technology
3.1 Features of CDN technology
(1) According to the user's geographical location and connection bandwidth, the user is connected to the nearest server, and the access speed is fast.
(2) Global load balancing, improve the utilization of network resources, and improve the performance and quality of network services.
(3) The hot content is actively transmitted, automatically tracked, and automatically updated.
(4) The network is highly reliable, usable, fault tolerant and easy to expand.
(5) Seamlessly integrate into the original network and site.
3.2 Advantages of CDN technology
(1) It can reduce the consumption of network bandwidth, reduce the delay of network access and user response time. Improve network performance and the availability of website content.
(2) Improve the management and control capabilities of website resources, intelligently assign routes and perform traffic management.
(3) The content sent is protected, and unauthorized users cannot modify it.
(4) The content provider can decide the content of the service locally, and the content is dynamic.
(5) Content providers improve the quality of service while reducing costs, providing more content and speed.
(6) New equipment can be added linearly and smoothly to protect the original investment.
Because of the above characteristics and advantages, CDN technology can accelerate and improve the use of broadband streaming media, making Internet multimedia users more popular, including online play, music on demand, live TV, games, etc., greatly promoting the development of online applications and services. .
4, IPTV system composition
IPTV (Internet Protocol TV or Interactive Personal TV), also known as interactive network television, is an Internet-based multimedia communication technology. IPTV utilizes the infrastructure of broadband networks, using home televisions or computers as the primary terminal equipment, transmitting television signals over the Internet Protocol (IP), and providing home users with a variety of interactive digital media services, including television programming.
The working principle of IPTV is to encode and process the TV signal data at the source end into a data format suitable for IP network transmission, and then transmit it through the IP network, and finally decode it at the receiving end, and then play it through a computer or a television. Due to the high data transmission speed requirements, the latest high-efficiency video compression technologies, such as H.264, MPEG4, etc., are used. The system composition of IPTV is shown in Figure 1:
(1) IPTV terminal
At present, IPTV terminals mainly have three forms, namely, PC, set-top box + ordinary TV set and mobile phone.
(2) Access system
The access system mainly provides an access function for the IPTV terminal, so that the IPTV terminal can smoothly access the IP bearer network. At present, ADSL as a way of broadband access network still dominates in a few years, and Ethernet access methods are gradually increasing. Using FTTC/FTTB, combined with ADSL, SDSL, Cable Modem and other technologies, FTTC+HFC can also be used to provide broadband access to users.
(3) IP bearer network
The bearer network used for transmitting IPTV is based on the TCP/IP protocol and may be a public network. It can also be a private network.
(4) Content Media Service System
This part mainly completes the digitization of the program, encodes and compresses the original program, and can be uploaded on the IP network.
(5) Program source
The program source can be a camera, a television station, a VCD disc, a satellite input signal, and the like.
5. Application of CDN technology in IPIV
The IPTV system has high requirements for the quality of service of users, and it is necessary to ensure smooth playback. In the WAN, after a very complicated route from the client's client to the streaming server, it is difficult to ensure smooth playback. In order to overcome the constraints brought by the complex route of the network, the end-user on-demand service must be implemented in the IPTV through the edge service, so to effectively distribute the content from the central server to the edge server, the content can be distributed from the central storage server through the CDN. Go to the edge server.
The core idea of ​​the CDN is to push content from the center to the edge of the user. The user can obtain the required content in the vicinity, which not only effectively improves the performance of the user to access the content, but also effectively reduces the pressure on the central device and the backbone network. With CDN, content distribution can be changed from a single central structure to a distributed structure, improving the responsiveness of users to the website. Therefore, CDN can improve the efficiency of information flow in the network, and comprehensively solve the problem of improving the response speed of user access due to problems such as small network bandwidth, large user access, and uneven distribution of network points.
Although CDN is not a new concept, its development has been for many years, but CDN does not have a unified protocol standard. The CDN solutions of various manufacturers are different in implementation, but the functions mainly included in a CDN network. Entities are the same, including content caching devices, content switches, content routers, CDN content management, and more.
The content caching device is a service providing point of the CDN, and is a content providing device for the end user, which can cache static web content and streaming media content, realizes edge propagation and storage of the content, so that the end user can access nearby, so generally deployed in the centralized User access points, devices that complete content edge storage are usually implemented using Cache technology. For the storage in the Cache node, it is a key issue in Cache design. The factors to be considered include functional and performance aspects: functional support for various content formats, partial cache support, and performance support. Capacity, multi-file throughput, reliability, and stability.
The content switch is in the user access concentration point and POP point, and can perform cache load balancing and access control on the content. In many cases, the content cache is concentrated on one device. The content switch can balance the load of a single point of multiple content caching devices, which provides content services based on end user sessions and specific content requests. The content switch is one of the optional components of the CDN. For larger user access points, the content switch can improve the availability of the site.
The content router is responsible for scheduling the user's request to the appropriate device. The content routing is usually implemented by a load balancing system, which implements the content routing function of the CDN. Its role is to dynamically balance the load distribution of each content cache site, select the best access site for the user's request, and improve the usability of the site. Content routing is based on network topology, network latency, server load and rules, etc., and specifies that the optimal site provides services to specific content requests. Content routers can route based on a variety of factors, including site-to-user proximity, content availability, network load, device status, and more. The load balancing system is the core of the entire CDN. The accuracy and efficiency of load balancing directly determines the efficiency and performance of the entire CDN.
The content management system is mainly responsible for the management of the entire CDN system. It is an optional component of the CDN. Its role is to manage content, such as content injection and distribution, content distribution, content review, content services, etc. The user of the content distribution and transmission service or the service provider can monitor, manage, or control the distribution of network content, device status, and the like as needed.
6, the technical realization of CDN
At present, the products and equipments for the CDN business are different from each other. The solution is also very different, and the products of various manufacturers are not compatible. The following describes the technical implementation of several representative companies for the CDN business.
6.1 Inktomi's CDN technology implementation
Inktomi's CDN system is a suite of software that provides distribution and synchronization of web content in a distributed web environment. It consists primarily of content distributors, content managers, and their agents.
(1) The content distributor distributes web content to multiple web servers and cache servers through reliable and secure means, and ensures the synchronization of its contents.
(2) The content manager collects the status of each web server and cache server, and provides centralized management functions. Communication between the content distributor and the content manager is done by the controller of the system.
6.2 Cisco's CDN Technology Implementation
Cisco's CDN system consists of five technologies: content distribution and management, content routing, content edge propagation, content exchange, and intelligent network services.
(1) Content distribution and management technology can realize automatic distribution of content while providing real-time monitoring. The Content Distribution Manager (CDM4670) enables efficient and centralized control of the entire CDN network, working in conjunction with content engines and content routers. Content routing technology ensures content availability and provides global load capacity; content exchange technology can intelligently implement information at the POP (demo point) or distributed node of the distributed data center based on content availability, application availability, and server load Load balancing
(2) The content router (CR 4450) can make routes based on various factors, including site-to-user proximity, content availability, network load, device status, and the like. Locate the most appropriate site response content request;
(3) Content exchange provides burst access protection, URL-based server load balancing, dynamic content replication, and dynamic content redirection. Cisco WebNS software is used to provide content routing services. By dividing users and content into different areas, content requests can be selected to select the best sites and servers:
(4) Content edge propagation technology can ensure that the network submits content to end users, accelerates content dissemination, and reduces the burden on WAN and source content servers. The content engine is a content edge propagation device. The content engine is a content edge propagation device. The content may be extracted by the content engine from the source content server according to a special indication, and the frequently accessed content is customized through the transparent cache;
(5) Intelligent network service technology can provide multiple intelligent services including various IP infrastructures, such as security, QoS, VPN, and multicast.
6.3 F5 company's CDN technology implementation
F5's CDN solution is based on content delivery network services and is built on a cache. Its infrastructure includes: content replication, high reliability and load balancing, caching, full support for web and cache servers, and network management.
(1) The Global Site Controller is responsible for managing content replication within the CDN, pre- and copying content to the appropriate cache and web server. Automatically distribute and synchronize to all sites within the network.
(2) BIG-IP controllers and 3-DNS controllers are used to provide local and regional high reliability and intelligent load balancing. BIG-IP directs user traffic to the best performing network services and cache servers. Provides rich features for management applications (cookie exchange, URL exchange, stable reuse methods, exploration and verification of content and applications, etc.). It is most efficient by placing it in different cache arrays to distinguish individual objects (rather than domains or URLs). When the content is updated. Manage communication between the server and the global site. Provide additional security features (default gateway, NAT, SNAT, packet filtering, port mapping). 3-DNS addresses user needs and guides them to the best sites in the world, providing intelligent global load balancing and high reliability through network and site management, providing disaster recovery for redundant site start/boundary points for monitoring and reporting And charge sending statistics, using performance-based user redirection.
(3) EDGE-FXTM cache can increase network site performance, increase network bandwidth capability, and accelerate content delivery to end users. At the edge of the network close to the end user, allowing the storage of web data, retrieving data from the edge of the network.
(4) Support for geographically distributed web and cache servers and non-F5 product integration includes all IP-based server technologies, including ERP applications, all web-based applications and email applications.
(5) The SEE-IT Network Manager transmits analysis and reports for the network in real time, including rules for configuring, billing, and coordinating the distribution of cached content.
7, the conclusion
At present, edge access of CDN on IPTV network is an effective way to improve QoS of IP bearer network. Many operators deploy CDN/MDN on broadband network, which lays a good foundation for the construction of IPTV network. The emergence of the CDN network has maximized the use of Internet resources. It will greatly promote the development of domestic IPTV services.
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