Is Symmetrical Bandwidth a Myth or a Must?
To build efficient and affordable networks, technologies must meet consumers’ true needs —more capacity in the downstream direction. Consumers, businesses and governments worldwide understand the importance of next-generation services for creating a sustainable future. With the proliferation of advanced and interactive services — and high demand for premium quality of experience (QoE) — traffic is growing in both downstream and upstream directions. But how will it proceed? Will we need symmetrical bandwidth? To answer these questions, we analyzed traffic patterns, consumer behavior and service evolution to help pinpoint effective ways to evolve broadband networks, encourage investments and avoid unrealistic goals that are not aligned with digital society’s needs. Our analysis indicates that, overall, broadband traffic will increase faster in the downstream direction. Therefore, to accommodate long-term growth in the most efficient way, technologies should be designed to meet this requirement. While symmetrical bandwidth offers a number of benefits, mandating symmetrical bandwidth for consumers will hamper future investments, delay the digital agenda, and unnecessarily disregard the strengths of existing broadband infrastructure.
Surfing downstream, swimming upstream
Consumer traffic has changed greatly since triple play services emerged in the 1990s. It started as highly asymmetrical traffic with downstream volume 10 times greater than upstream. Then it became less imbalanced with the growth of peer-to-peer and interactive services. Now upstream-hungry services, such as picture and video storage in the cloud, social media and video chatting, are being rapidly adopted. But most operators worldwide offer only a few Mbps (or less) in the upstream direction. As a result, upstream capacity has become a concern. Everyone benefits when broadband networks provide an abundance of upstream bandwidth:
- For end users — It helps improve QoE and enables new services.
- For content and application providers — It expands the market for innovative services.
- For operators — It allows service differentiation and higher revenues.
Fortunately, today’s technology can accommodate increased upstream speeds — through deployment of optical networks or through upgrades to legacy copper and cable networks. These technologies were intentionally designed to be asymmetrical, so they could carry the heavier volumes of downstream traffic. On the other hand, SHDSL, a symmetrical digital subscriber line (DSL) technology, has been available for several years. In 2011, roughly 1% of all DSL lines shipped worldwide were SHDSL. They were deployed mainly for business services. Next-generation fiber and copper technologies will continue to enhance capacity in both directions, as shown in Figure 1, with keen attention to cost to expedite deployments and adoption.
The evolution of GPON technology offers a good example. It has been standardized to have four times more capacity downstream than upstream, striking a smart balance between investment and bandwidth demand.
An asymmetrical future
Despite new services demanding symmetrical bandwidth, the most popular and bandwidth-intensive services remain highly asymmetrical. This results in overall asymmetrical traffic, as shown in Figure 2. (Note that when traffic volume is high, traffic asymmetry is also high.)
Overall traffic is also becoming more asymmetrical over time. In triple play access networks, the largest bandwidth demand comes from downstream IPTV video and Internet video. These bandwidth-consuming services are also the fastest growing, so overall traffic will become even more asymmetrical. The future is likely to bring changes in services and usage but not in the asymmetric nature of Internet traffic. The following trends illustrate why:
- Entertainment — The average person downloads more content than he uploads. According to May 2012 Internet traffic statistics, 48 hours of video were uploaded every minute on YouTube, and almost 70,000 hours were downloaded in the same period. This pattern produces a 1500:1 asymmetry in YouTube usage.
- E-education — The Internet will become an increasingly important mode of education. Yet the amount of information that students download will be much higher than they upload.
- E-health — Remote patient monitoring is showing strong growth, with an 18% compound annual growth rate (CAGR) expected from 2010 to 2016. Upstream capacity is important for this application. However, the transmission of digital data and occasional compressed video will not require a huge amount of bandwidth — and will not impact the overall traffic asymmetry. Most of today’s wireless and fixed access networks can cope with these requirements. And the future of remote monitoring relies on factors other than bandwidth limitations.
- Home monitoring — Home monitoring is very similar to remote patient monitoring. But the bandwidth requirements upstream are even lower because of the way the video compression tools work. After the first video image is sent, subsequent images are comprised of their difference from the previous image. Because the monitoring occurs when nobody is at home the video image is static, and there is very little to transmit.
- Video conferencing — This service is driving upstream bandwidth. It is symmetrical for one-to-one communication, but it becomes asymmetrical for multipoint conferencing with three or more parties. Ambient video is an emerging form of video conferencing and a potential source of sustained user-generated video. Like instant messaging, this background application allows communication among several friends. It may be symmetrical or asymmetrical, depending on the number of participants.
The importance of upload speeds is emphasized by increases in user-generated content, interactivity, social media, video conferencing and the Internet of things (which involves communication between billion of sensors). However, these same applications and others will impact downstream speeds as well. As a result, broadband traffic will remain asymmetrical in the future, as confirmed by independent industry studies conducted by Bell Labs, Cisco VNI, CableLabs and Sandvine. These studies foresee three to five times more bandwidth in the downstream direction.
Will the cloud change everything?
The ability to store and run applications on cloud servers opens an opportunity to revolutionize how telecom services are delivered and consumed. Cloud applications are now moving from the enterprise market into the consumer segment. For example, cloud-based gaming services are already available, bringing the following benefits:
- End users don’t have to worry about game-player upgrades and compatibility issues.
- Gaming developers can reduce the costs of manufacturing, distributing, reselling, and user support, while increasing revenues by eliminating piracy.
These benefits could easily be replicated among other consumer services, promoting further expansion to the cloud. So how will this impact bandwidth consumption? The probable evolution of network gaming may offer an answer. In network gaming, traffic is highly asymmetrical. Control is sent from the player, and video is sent to the player. The evolution of gaming toward greater realism will drive an increase in video quality with a corresponding increase in downstream traffic. The fundamental changes brought by the cloud may be accompanied by the following technology advances:
- Improvements in video compression techniques will enable networks to cope with the explosion of video traffic, larger TV screens and higher resolution.
- Intelligent network software will perform incremental archiving which stores only those files that have changed since the previous back-up.
- Content will be uploaded only if it is not already available in the cloud. If a user wants to store content such as music or video, on his private cloud space, the application will fetch it from the cloud and not from an end-user device.
- To relieve prime-time congestion when people may watch and record several video streams simultaneously, content to be recorded will be stored in the cloud, then delivered later.
These advanced technologies can ensure that network resources, including bandwidth, are used cost effectively, and cloud-based consumer services will not change the asymmetry of bandwidth. Another long-term trend is toward full virtualization. In this case, cloud applications running in the cloud will communicate with web browsers or thin clients running in the home. Most of the traffic will travel downstream, and therefore, will be asymmetrical.
Is symmetrical bandwidth a must for a digital society?
The broadband communications revolution shows how innovations in services and technology can rapidly reshape how society communicates, works, learns and entertains. Yet, the biggest investments are still ahead. To build the most efficient networks, with the right balance of capacity and cost, industry experts have focused on the standardization and design of next-generation networks that can accommodate growing bandwidth demand for years to come. Analyses of traffic patterns, consumer behavior, and service evolution indicate that despite an increase in upstream traffic, broadband traffic will increase faster in the downstream direction. Therefore, most technologies are designed to meet this requirement. Symmetrical bandwidth is a great way for operators to differentiate a service offering, generate new revenue streams and spur innovation. However, mandating symmetrical bandwidth for the consumer market segment will hamper future investments due to higher costs. In addition, it will delay achievement of the digital agenda, lead to new cycles of network design and standardization, and unnecessarily disregard existing industry efforts to build broadband infrastructure. In the quest to bring high broadband to more users, the focus should be on how networks are really used, because that is the only way to make them efficient and affordable. To contact the authors or request additional information, please send an e-mail to email@example.com.
- Worldwide Tables (Dell’Oro Group: 2Q12 Access Quarterly report)
- Global Internet Phenomena Spotlight, 2012, Sandvine Incorporated