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Optimal 4K Video Delivery

Telecom operators are discovering that Optical Transport Networks (OTNs) are a strategic opportunity for transformation by leveraging the value of 4K video services. With 4K terminals gaining wider penetration and more content becoming available, telecom operators see 4K paths as a way to differentiate themselves from competitors. As a result, these operators are shifting focus from simply offering network connectivity to adopting service- and experience-driven approaches to network construction that will optimize the user experience.

4K Drives Network Upgrades

The issues that had delayed the development of 4K video, such as lack of 4K programming, limited bandwidth, and high prices for 4K displays, have gradually been resolved. For example, in the U.K., British Telecom (BT) achieved 23 percent growth in video services by launching the BT Sport video service over a newly constructed Next-Generation Access (NGA) network. In China, Sichuan Telecom has more than 5 million video service subscribers, 1.2 million of whom subscribe to 4K video — and the number is growing rapidly. In South Korea, the top three operators offer 4K services and expect to achieve 100 percent coverage for 1 Gbit/s access by 2020.

Driven by the development of technologies such as 8K video, Augmented Reality (AR), Virtual Reality (VR), and holography, video will continue to be the largest and fastest growing source of network traffic.

Metro Ethernet Challenges

The traditional Metro Ethernet (ME) networks that suit voice and data services are not a good fit for streaming video data.

A key difference between voice and video services lies in the size and duration of their bandwidth use. For voice calls, average connection lengths are in minutes and dozens of kilobits per second. For video services, connections for feature films will last up to two hours and require orders of magnitude of more bandwidth.

At 30 Mbit/s per user for 4k video services, traffic carried over Metropolitan Area Networks (MANs) is expected to increase by up to seven times within three years to support the immediate growth of 4K video consumption and by at least ten times in five years.

Rising network loads are accompanied by increases in packet loss and delay and, in fact, multiple researchers have published results indicating that video streams are on the order of one hundred times more sensitive to corruption by packet loss or delay than audio streams.

As recommended by Technical Report TR-126 from the DSL Forum, a non-profit corporation organized to create guidelines for Digital Subscriber Line (DSL) network system development and deployment, the packet error and drop rate in HD video transmission should be less than 10-5. When packets are forwarded hop-by-hop over the Internet, delay occurs, although this delay is generally shorter than the normal 50 μs when network devices are not congested. Even high-priority services are subject to delays that may reach the level of milliseconds or even seconds on a single device.

The major requirements of video services today are high bandwidth, low packet loss, and low delay. Traditional ME network characteristics, however, include hop-by-hop forwarding and layer-by-layer convergence, both of which lead to high packet loss and long delays. In addition, the costs of ME networks are high.

Extending the OTN to Central Office Sites

Several measures are available to provide users with optimal video experiences, minimize the number of converged layers and nodes, and reduce per-bit network costs. First, the architecture of traditional ME networks can be optimized to take on a flattened structure with three layers:

  • Smart Central Office (CO)
  • Broadband Network Gateway (BNG)
  • Core Router (CR)

Once this structure is in place, the OTN can be extended to CO nodes. Specifically, a large number of Optical Channel Data Unit-k (ODUk) hard pipes are used to connect Optical Line Terminals (OLTs)/Hubs and core-layer devices. These connections transform the IP ring topology into a tree network that allows service traffic to be forwarded from IP edge nodes to the core nodes with a single hop. This architecture eliminates intermediate hops and packet forwarding, which reduces forwarding costs, delays, and packet loss. With this architecture, video services on Content Delivery Networks (CDNs) are becoming as close as one hop away from the requesting terminals and being transmitted with high bandwidth, low delay, and zero packet loss, thereby delivering the best 4K video experience to users.

Simplified Network Architecture

Telecom operators working with MANs have the advantage of a simplified architecture that enables them to adapt to a fast-changing service landscape. For example, Huawei uses the OTN as the transport layer, which helps operators construct simplified networks that extend the OTN to COs. In this architecture, the OTN delivers many advantages.

First of all, the OTN ensures sufficient pipe resources. Wavelength-Division Multiplexing (WDM) technology offers an extraordinary capacity. With WDM, one pair of optical fibers supports concurrent transmission of traffic over as many as 80 channels, each providing up to 200 Gbit/s bandwidth for a total bandwidth of 16 Tbit/s. With the use of flex-grid technology, the bandwidth of one pair of optical fibers can exceed 20 Tbit/s.

In addition to increased raw bandwidth, for all practical purposes, the OTN exhibits zero packet loss. Packets are lost with other transport technologies for three main reasons. First, packets may be discarded due to line-bit errors. In contrast, OTNs have forward error correction capabilities with unparalleled Bit Error Rates (BERs) up to an order of magnitude below 10-12. The second reason for packet loss is device processing errors. Since the WDM uses hard pipes and the OTN mapping-based encapsulation mode to transmit services transparently without further processing, the probability of packets being dropped by devices is effectively zero. The third reason for packet loss is protective failovers. The WDM network is capable of implementing fast protective failovers (within 50 ms). When a working path is interrupted, the WDM network can restore dropped packets from the buffer of the protection path, thereby ensuring zero packet loss.

Another advantage of the OTN is minimum delay. Congestion over forwarding nodes is the prime cause of delay in conventional networks and occurs only in locations where traffic is forwarded from a larger pipe to a smaller one. In contrast, the WDM/OTN utilizes straight-through hard pipes and is able to forward all received traffic without any congestion, which reduces delay in video services.

Additionally, OTN simplifies network Operations and Maintenance (O&M). Huawei’s Smart OTN O&M solution accomplishes this simplification by providing design planning tools, automated optimization and commissioning tools, visualized dashboards, and a 4K service-experience-indicator qualitative management system. These tools enable visualized and manageable device layers, with each device layer having a clear alarm and monitoring interface that supports quick and accurate fault location. Management and maintenance are made easier and Operating Expenses (OPEX) are significantly reduced, while ensuring a smooth End-to-End (E2E) 4K O&M experience.

By leveraging E2E OTN products and services, Huawei is assisting telecom operators to restructure and simplify their transport networks.

WDM-to-OLT Architecture

Vodafone Netherlands (VDF NL) began building a new WDM network in 2009. In this project, VDF NL used Huawei OTN devices to replace aging Synchronous Digital Hierarchy (SDH) and Point-to-Point (P2P) 10G WDM devices. New equipment with 40G wavelengths has been deployed over the entire network. As the 100G technology gradually attained maturity, VDF NL also deployed 100G wavelengths on the fixed network. In planning a Fiber-To-The-Home (FTTH) transport network, VDF NL relocated WDM devices originally deployed on the backbone (involving about 70 sites) to OLT sites. The upstream traffic of OLTs was transported through WDM devices directly to switching sites, which provided the fixed network with high bandwidth for one-hop transmission of traffic.

Fire and Forget

Swisscom, a major telecommunications provider in Switzerland, used a different approach called ‘fire and forget’ to implement a simplified network. In this approach, traffic is forwarded by WDM directly to OLTs/base stations. Each link provides direct GE bandwidth to the core layer without convergence.

Compared with financial figures from 2010, Swisscom invested more than USD 2 billion in additional funding in recent years on network restructuring or Capital Expenses (CAPEX) but saved about USD 3.4 billion in OPEX.

Looking Ahead

Users relentlessly pursue a better service experience over more diverse terminals, and more flexible viewing options ensure the continuous growth of video traffic. Additionally, market demand for cloud storage and cloud computing will continue to rise and push telecom operators to increase investment in their Data Center (DC) infrastructures. Against this backdrop, DC-centric network architectures are earning wide acceptance by telecom operators, who are starting to migrate services, including video services, to DC-centric architectures.

Telecom operators are moving WDM devices downward to MANs and access sites, and using the OTN to construct simplified transport networks for 4K video services. The current development phase, focusing on hardware, can be dubbed ‘Simplified Optical Network 1.0.’

Huawei continues to invest in Software-Defined Networking (SDN) development to increase the level of network intelligence. Looking ahead to the year 2020, Huawei will develop more solutions for DC-centric services, helping construct telecom networks that have enhanced software capabilities with auto-detection, self-healing, and self-organization. We can soon expect the arrival of ‘Simplified Optical Network 2.0’!

By Wang Jinhui

Deputy Director, Fixed Network Transmission Marketing Support Department, Huawei Technologies Co., Ltd.

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