The purpose of the bearer network is to provide the best delivery path for multiple services. The service characteristics determine which bearer scheme to choose, and need to consider the three factors of bandwidth, service experience, and cost. In the voice era before 2005, TDM voice services occupy small bandwidth, but are highly sensitive to delay. The bearer network needs high quality and high reliability. The SDH network perfectly matches these requirements, but the bandwidth is limited and the cost per bit is high. After 2005, the data service has increased dramatically. The service characteristics are large bandwidth, high convergence, and low real-time requirements. Therefore, the bearer network using statistical multiplexing is the best choice, allowing N users to share a bandwidth and reduce each user. cost.
In recent years, video services have grown rapidly, and video streaming has flooded people's fixed and mobile lives, bringing the average revenue per user (ARPU) to more than 20%. The video service itself also ranges from the original low-definition (LDTV, resolution 340*255 pixels) to standard definition (SDTV, resolution 720*576 pixels) to the current popular HD (HDTV, resolution 1920*1080 pixels). Nowadays, the next generation of ultra-high-definition video is quietly emerging, and it is now possible to restore the true ultra-high definition 4K video (UHDTV, 3840&TImes; 2160 pixels) and 8K video (UHDTV, resolution 7680&TImes; 4320 pixels). Especially since 2014, many 4K resolution ultra-high-definition TVs are refreshing; Japan, South Korea, the United States, France and other countries are also stepping up to build a 4K TV live broadcast platform, and experimented at some world-wide gatherings. The transmission, these marks the video business is about to enter the era of ultra high definition.
The high-definition video service features bring new challenges to the bearer network :
1) Although compression coding technology and transmission channel coding technology continue to innovate to some extent to optimize video traffic, it still cannot change the trend of rapid expansion of bandwidth consumption of high-definition video services. The requirement for access bandwidth of 4K video has been increased to more than 30M, which is 20 times that of standard definition video. The bearer network must face dozens of times of increased bandwidth demand.
2) Compared with the data Internet service, the video service belongs to a high-bandwidth long-term online service, and the service convergence ratio is low.
3) The video service is sensitive to delay and packet loss. The faulty packet loss and network congestion loss in the bearer network directly triggers video mosaic or jamming. The current bearer network mostly adopts multi-layer aggregation mode, and the video service passes through. Multi-hop forwarding and multi-layer convergence, which all seriously affect the user experience.
4) The video service is mainly on-demand. Most of the current CDNs are not hung down, resulting in the backbone and metro cores carrying a large number of video streams, and the bandwidth is facing huge impact.
In summary, the video service has the characteristics of large bandwidth, low convergence, and high real-time requirements. In order to bring the best video experience to customers, and consider the cost per bit network, OTN technology is used to optimize the traffic path and build a minimalist architecture bearer network, which is the best choice for carrying video services.
1. Minimalist OTN architecture, better OPEX for video services
A traditional Ethernet bearer network generally has a five-layer structure, including ME1-ME2-BRAS-PE-CR, and video services need to be forwarded layer by layer. Among them, ME1-ME2-BRAS is mostly direct fiber connection, and BRAS-PE-CR is generally carried on traditional wavelength division or OTN network. There are many types of devices, and it is difficult to manage and maintain the fiber directly. Moreover, layer-by-layer forwarding leads to long network service paths and large delays, which affect the final customer experience. At the same time, due to the large video bandwidth occupation, the convergence ratio is small. According to statistics, the intermediate path of the Metro Ethernet metropolitan area network accounts for 60% of the traffic, which consumes a large amount of transmission resources.
With OTN as the transport layer, the Ethernet network architecture can be optimized to the flat and minimalist three-layer network structure Smart CO-BNG-CR. By using OTN instead of the previous fiber direct connection, OTN can provide a visual logical direct path between each network layer and device, optimize the traffic path, greatly reduce the delay, and provide customers with a better experience.
At the same time, compared with optical fiber, OTN is a visually manageable device layer. Different device layers have clear alarm and monitoring interfaces, which make fault location faster and more accurate, easier to manage, simpler to maintain, and greatly reduce OPEX.
2. OTN network's large bandwidth provides sufficient pipeline resources for video services.
The most critical feature of a WDM/OTN network is its large capacity. Different from other bearer technologies, due to the use of wavelength division multiplexing technology, a pair of optical fibers can simultaneously transmit up to 80 wavelength channels, and the single channel bandwidth can reach 100G/200G. A pair of optical fibers in the WDM/OTN network can provide 8T/16Tbit super bandwidth and spike 10G/40G/100G pipes to provide sufficient bandwidth resources for video services.
The OTN network is an intelligent networked WDM network. It not only inherits the advantages of the large-scale pipeline of the WDM network, but also provides high-quality bandwidth resources for video services that are large, flexible, and fast. Based on the OTN technology, the WDM network uses standardized ODUk granules to map and encapsulate services, decoupling the service side and the transmitting side, enabling flexible application of large bandwidth, that is, multiple small granular services can be carried in a 100G or even 200G. On the large channel, the OTN network can implement fast end-to-end service channel establishment and implement SDH-like simple operation and maintenance.
3. OTN network has low latency and "0" packet loss, providing excellent experience for video services.
In addition to bandwidth, network performance parameters that affect the video experience include packet loss rate and latency:
There are three main reasons for packet loss: the first is the line error. The WDM/OTN network is initially positioned as a high-quality trunk transmission. The line transmission error rate is very strict and has strong forward error correction capability. The most basic error rate after error correction is less than 10-12. The ability to solve line errors is unmatched. The second is the device loss. WDM/OTN is a hard pipe. It adopts the OTN mapping encapsulation mode and does not process packets and transparently transmit services. Therefore, device packet loss is reduced to zero. The third is the packet loss caused by the protection switching. The WDM/OTN network can implement lossless protection switching. After the working path is interrupted, the lost packet is recovered from the Buffer of the protection path, and the packet is lost after the fiber is broken.
Analysis of the cause of the delay found that congestion is the culprit of delay, congestion will only appear in the large bandwidth into the small pipeline, WDM / OTN is a straight through the hard pipeline, how much, how much, never congested. In addition, due to the flattening of the WDM/OTN booster bearer network, the channel with direct wavelength is adopted, and the end-to-end path of the video service is optimized, and the delay is greatly reduced.
The WDM/OTN bearer network maximizes the packet loss rate and latency, resulting in an excellent video service experience.
High-definition video has gradually become the dominant Internet traffic in the future. As a bearer network, in the face of the already coming video flooding and end-user experience requirements, the OTN network returns to the hard pipeline with a minimalist architecture, perfectly matching the three basic needs of video, providing customers with The ultimate experience is the undisputed best choice for video delivery bearers
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