Bandwidth Proximity Control. Reduce latency to milliseconds. NSN White paper Reduce latency to milliseconds March 2013

Transcription

1 NSN White paper Reduce latency to milliseconds March 2013 Bandwidth Proximity Control Reduce latency to milliseconds 2013 Nokia Solutions and Networks. All rights reserved.

2 CONTENTS Executive summary 3 The rapidly growing use of mobile applications demands reduced network latency Why low latency matters 5 Key success factors for improving network latency 6 Nokia Siemens Networks recommended approach to reducing network latency Nokia Siemens Networks is making low latency networks a reality Abbreviations

3 Executive summary Low latency is the key to instant satisfaction for mobile broadband users. Latency has a major impact on services and applications, such as mobile video communication, live video streaming and multi-player gaming. It may be impossible to predict the kinds of applications that people will be using in five years time, but one thing is certain we re going to see more emphasis on realtime performance in mobile services. Gamers are especially sensitive to latency, since their applications call for latencies below 10 milliseconds. Similarly, many automated trading applications are also highly sensitive to latency, transactions can take place in milliseconds and delays could cause financial losses. Three critical parameters need to be addressed to create a low-latency mobile network: bandwidth, proximity and control. While bandwidth helps to improve the overall customer experience, including latency, simply adding more and more capacity to a network is economically not feasible. Latency can be lowered significantly by implementing QoS differentiation and policy control to help ensure that latency-sensitive traffic is prioritized through the network. The third aspect, proximity, relates to the laws of physics. Data travels at a fraction of the speed of light in a network, so bringing content closer to the end user can have a dramatic impact on the latency experienced by the user. In mobile networks, the closest you can get to end customers is the base station. Latency is an opportunity for network operators to change the game in content delivery by enhancing the customer experience of latency-sensitive applications. It s a big challenge, but adding capacity, improving traffic control and placing content close to users will lead to a noticeable better customer experience and create substantial business benefits for network operators. The rapidly growing use of mobile applications demands reduced network latency The use of latency-sensitive applications in mobile networks is growing. Today, 69% of all mobile traffic is streaming video and this proportion is expected to grow to 76% in 2020 (Cisco VNI 2012). In the future, latency will become even more important because applications will go far beyond those of today. Remote real-time control of machines, 3D-video and cloud-based gaming are expected to be among the next wave of applications and will revolutionize the way people work, learn and play. Latency determines the perception of speed in about 80% of all mobile broadband uses. Realtime functionality demands the lowest possible delay in the network, therefore latency will become a business opportunity for operators. The loading time of web pages is a good example of how response time interferes with the customer experience. Studies into consumer response to the performance of a travel shopping site indicate that people expect a loading time of less than three seconds. In 1999, consumers expected eight seconds load time, and in 2006 less than four seconds. Consumers are clearly

4 becoming more demanding. Today, 65% of year-olds expect a web page to load in two seconds or less. It is highly likely that in the near future, people will be looking for a sub onesecond browsing experience. Awareness of how latency affects the customer experience has motivated over-the-top (OTT) providers to tailor their messaging protocols to minimize latency over today s networks. However, since the biggest factors affecting latency are in the networks, operators are better placed to address the issue and also potentially benefit commercially by reducing latency. Nokia Siemens Networks forecasts a growth in partnerships between OTT providers and network operators. The OTTs want people to experience their content and services with the best possible quality. Operators also re-position themselves within the value chain, to break from their perception of being a bit-pipe. The majority of today s mobile networks have an end-to-end delay in the range of 200 to 500 milliseconds. However, measurements of latency of 15 to 20 milliseconds in LTE networks, as well as 20 to 50 milliseconds in HSPA networks prove that end-to-end latency can be lowered. The effect of latency on people Response time is relevant for every interaction of humans with machines. Some 20 years ago, three response time limits were defined by Nielsen*. 0.1 second gives the feeling of instantaneous response that is, the outcome feels like it was caused by the user, not the computer. This level of responsiveness is essential to support the feeling of direct manipulation. 1 second keeps the user's flow of thought seamless. Users can sense a delay, and thus know the computer is generating the outcome, but they still feel in control of the overall experience and that they're moving freely rather than waiting on the computer. 10 seconds keeps the user's attention. From 1 10 seconds, users definitely feel at the mercy of the computer and wish it was faster, but they can handle it. After 10 seconds, they start thinking about other things, making it harder to get their brains back on track once the computer finally does respond. *Nielsen Response time limits

5 Why low latency matters Looking into latency-sensitive services in mobile networks provides some insight into how latency in networks needs to be improved. Fast browsing requires more than just bandwidth Web page performance depends on the technology selection of web developers and web hosters. Advanced web developers will create pages with html compression, css and js files. They use optimized images, avoiding bad request and redirects and other techniques. Moreover, the dynamic and diverse development of web browsers and servers often focuses on speed as a competitive advantage. Web page download enhancements such as opening of several simultaneous parallel TCP connections and http pipelining are used to deal with issues in high delay networks. Today, during an average web page download, information must be retrieved from 90 different resources within six different domains. The browser has to deal with several TCP connections to those domains and resources, without being able to load everything in parallel. Typically, the response time should be less than 50 ms for each individual connection. Video and voice calls are strongly affected by delay For a fluid conversation, the mouth to ear delay should be less than 150 ms, otherwise the participants may detect a pause and take that as their cue to speak. By time their words arrive at their destination, the other speaker has already begun the next sentence. A conversation becomes very difficult at around 400 ms mouth to ear delay. In video calls or video conferences, this 150 ms audio requirement applies as well, but lip synchronization also enters the scene. Visual lip movements must match with the spoken words, with any misalignment being referred to as skew. A skew of less than 20 ms is considered imperceptible. As the skew approaches 50 ms, some viewers will begin to notice the audio/video mismatch. As the skew increases, viewers become increasingly distracted from the video conference. When the skew approaches one second, the video signal provides no benefit, viewers will ignore the video and focus on the audio. So lip sync delay should be well below 50 ms. Web communication applications, such as Google Hangout, Apple Facetime and Skype, use low latency codecs and scalable video coding to make the applications more robust against network latency. Cloud-based applications are delay sensitive by definition Cloud-based gaming is another good example of a latency-sensitive application. For example in first-person avatar games, the time difference between a player performing an action and the result of that action appearing on the screen should be less than 100 ms. In some fast action games, latency in excess of 70 or 80 ms may be unacceptable. Typically, people expect instant response within a game of less than a hundred milliseconds.

6 Future latency demands As applications and services become more sophisticated and capable and as people s expectations grow, network latency will become an increasingly important consideration for operators. In general, an overall latency of 50 ms is likely to be the future benchmark. In today s mobile networks, this 50 ms figure is far from being achieved. However, measurements in LTE networks show significant improvements in latency because of high bandwidth and low latency technologies, Figure 1. Customer experience of network delay LTE measurements in tomorrow s network RTT 500 ms 400 ms Mobile network Fixed network RTT 50 ms 40 ms 300 ms 30 ms 200 ms 20 ms 100 ms 10 ms 0 ms MEA LAT APAC CEE NAM WE 0 ms 6pm 6am 6pm 6am 6pm 6am 6pm Source: Cisco Analysis of Ookla Speedtest Data, 2011 Source: Epitiro Ltd.: LTE Real World Performance Study (TeliaSonera) Figure 1: Measured latencies today and in the future Key success factors for improving network latency To understand how to improve network latency, we need to understand its sources. First the propagation delay, defined by the speed of light, depends directly on the distance the data must travel within the network. Second, serialization delay occurs at each interface that a data packet meets along its journey. This delay is defined by the length of the packet and the interface speed. Both delay sources can be estimated by determining the distance, number of nodes and bandwidth. However, complications arise when considering other sources of delay, such as the processing delay which happens in every node performing routing, switching, and inspection of the data packets. The processing time depends on the task and the actual processing load. Finally, other real-world factors can cause delay, such as congestion, faults and outages, maintenance interruptions, automated optimization routines, poor network management, and of course, simple human error. These unpredictable events cause packet queuing and packet losses. They are also almost impossible to predict and hard to control. Queuing is the time a packet has to wait until processing, which is extremely dependent on traffic load and its burstiness. All quality of service concepts address queuing delay, but the easiest way to control it is to optimize buffers in the network or minimize the number of nodes. After analyzing all these sources of delay we can come to two very simple conclusions. Firstly, it is possible to build and operate low latency networks. Secondly, operators are uniquely placed to

7 reduce latency and make a profit by doing so since they can add perceivable value for third parties in the value chain linking the content provider with the end user and offering a guaranteed level of service. Evolving network technologies will make it possible to improve network latency by a factor of three to five, depending on the network. Nokia Siemens Networks recommended approach to reducing network latency There are three key factors operators must take into account if they are to reduce latency: Access bandwidth is critical, especially for media-rich low latency applications like video conferencing and cloud-based gaming. The location of content and processing is crucial, as content that is in close proximity to the user will suffer less from network degradation. Also fiber distance will strongly limit the delivery of low latency services like telepresence or teleprotection. Instant network control is vital and requires a low-latency network architecture, latency-aware traffic engineering and latency-aware network/service control and management. Bandwidth, proximity and control are the three key words to remember for low latency success. Bandwidth: Improving the perceived network performance Access speed remains a limiting factor for the latency of media rich, time-sensitive applications that are particularly critical on shared radio, copper or fiber links under high load conditions. Therefore, building low latency networks requires a next generation access network that supports more than 100 Mbps per user. In addition to bandwidth, other ways to improve latency include the fast allocation of resources on shared media, fast retransmission procedures when transmission errors occur, the implementation of QoS capabilities and congestion control. Bandwidth also has an indirect impact on the perception of speed because it affects latency in a couple of different ways. First, the traffic load throughout of the network is important, because packets will be held up or dropped if they are forced to queue. Queuing (aka scheduling) delay is highly dependent on the burstiness of the traffic, as well as the overall load. In addition, packet processing resources may be spread more thinly under heavy load, leading to an increased delay at each network element. High bandwidth technologies such as LTE are evolving, and their high capacity will certainly help to reduce the load on each element and hence contribute to an overall reduction in latency. However, simply ramping up overall capacity to provide unlimited extra headroom at peak times is unrealistic from an economic perspective, so the key is to introduce mechanisms to manage the traffic more effectively, or have the capability to bring content closer to the subscriber.

8 Proximity: Bringing content closer to the user The propagation speed of light in fiber is around two thirds the speed of light in a vacuum, so in one millisecond a signal can travel around 200 km. A user in Europe accessing a server in the US will face a 50 ms round-trip time because of the distance, no matter how fast the network. The only way to beat this limit is to reduce the distance between user devices and the content and applications they are accessing. There are already content distribution networks (CDNs) that aim to address the distance issue by distributing static content to the edges of the network. Bringing the content 2,000 km closer to the user can potentially reduce the round trip time (RTT) by about 30 ms and page load times by more than 300 ms. Local caches are also an answer for many applications. Mobile operators possess a dense network of base stations that are in close proximity to the user. If these mobile assets are equipped with localized processing and storage, an accelerated and enhanced mobile broadband experience is the result. This also transforms applications that would typically reside in the cloud by moving them closer to the mobile user. Applications and content that are in close proximity to the end user will change the game in content delivery and raising the mobile operators contribution to the value chain. An IT-based capability located inside a base station will extend the application ecosystem, through the provision of unique service creation capabilities that open up new business opportunities towards contextualizing applications with real-time network data and augmented reality delivered from the curbside. Storage is relatively cheap, so that even a smartphone is today able to store tens of Gigabytes. That will grow to hundreds or thousands of Gigabytes in the future. Furthermore, the rising power of data analytics will make it possible to estimate very precisely which content an individual user will ask for next, at which location and on which device. However, some future applications such as cloud-based gaming depend on dynamically generated content that cannot be cached. That means processing capacity also has to be dispersed into local data centers or located right at the very edge of the mobile network. Control: Setting the right priorities Technologies such as Quality-of-Service (QoS) differentiation and policy control allow networks to treat different traffic streams according to their specific needs. So latency-sensitive media traffic might take a different path through the network or receive preferred treatment over plain data transfers. Networks are becoming application-aware, so that the priority scheduling and buffering available with QoS differentiation can minimize the impact of load-dependent delay. With improved control, the most sensitive, low-latency traffic could be charged at a premium, providing network operators with new ways to monetize services and content while complying with net neutrality regulations. Monitoring and optimization of network parameters in response to the real-time experience of users can also improve the perception of low latency networks.

9 Sufficient bandwidth for mediarich, delay-sensitive applications Average time to load a video frame 200 ms 150 ms HD SD/H.265 Full HD/H.265 UHD/H.265 high load Content & processing in close proximity to the user RTT: 1 20ms RTT: 5 10 ms RTT: ms Edge Rule definition Core >1ms/200km 100 ms 50 ms 0 ms SD HSPA HD LTE UHD B4G low load App identification and color marking Rule enforcement QoS differentiation Instant control based on network & user experience Figure 2: Reduce latency to milliseconds - bandwidth, proximity, control Nokia Siemens Networks is making low latency networks a reality Nokia Siemens Networks is committed to delivering on the promise of low latency networks. Therefore Nokia Siemens Networks has developed a variety of capabilities: Bandwidth: Commercial LTE networks deployed by Nokia Siemens Networks show an average round trip time of less than 20 ms. Benchmarks have also shown that average and peak data rates are significantly higher compared with other vendors implementations. Proximity: Only operators can place content close enough to users for hosting or providing low latency services. Furthermore, operators need to find ways to ensure their networks can continue to cope with rising growth of OTT content, while at the same time matching mobile broadband growth with associated revenues, with the provision of an enhanced experience. With our Content Delivery Network (CDN) functionality, content caching and processing are brought into the mobile operator domain. With a transformed base station capability, applications and content can be embedded further into the mobile network, right at the very edge, realizing mobile edge computing that is fully under the operators control. With these capabilities in place, operators can become more efficient and also provide value to potential partners in order to make money from content delivery. Conversely, the experience can also be optimized by making applications network-aware and equipping them with interfaces that instantly request the necessary connectivity. Control: Our Intelligent Broadband provides policy-controlled content delivery, content optimization and QoS and application aware RAN. Liquid Broadband is able to control the latency across the entire network - not just controlling parts of it. Customer Experience Management (CEM) for Liquid Net reveals how the network performs and what is affecting the customer experience. This monitoring analysis allows for latency to be managed as a KPI.

10 Significantly lower delay Much higher average data rates 400 ms worst delay average delay 100 Mbps peak data rate average data rate 300 ms 75 Mbps 200 ms 50 Mbps 100 ms 0 ms +41% Vendor B +96% Vendor C 25 Mbps 0 ms -26% Vendor B -47% Vendor C Figure 3: Reduce latency to milliseconds - bandwidth, proximity, control Source: Drive tests performed by Nokia Siemens Networks in a three vendor LTE network, 10MHz carrier LTE 850 MHz Nokia Siemens Networks is committed to delivering low latency networks. Low latency is a vital pillar of our technology vision for future networks.

11 Abbreviations CDN CEM CSS JS HSPA HTML LTE QoS RAN RTT TCP Content Delivery Network Customer Experience Management Cascading Style Sheets JavaScript High Speed Packet Access Hypertext Markup Language Long Term Evolution Quality of Service Radio Access Network Round Trip Time Transmission Control Protocol