Research of User Experience Centric Network in MBB Era ---Service Waiting Time

Transcription

1 Research of User Experience Centric Network in MBB ---Service Waiting Time

2 Content Content 1 Introduction Key Findings Research Methodology Explorer Excellent MBB Network Experience Indicators Waiting Time is Key Indicator to Experience in MBB Experimental Study Users Patiently Waiting Time Experimental Theory Result Analysis % Current MBB Network Reaches Excellent Network Experience Requirements G Network Waiting Time Investigation G Network Waiting Time Investigation Video and Web Content Development Raises Higher Demands on Network User Waiting Time Composition for Video Service Bandwidth Requirement for Different Resolution Video at Initial Buffering Time The Popularity of Large-Screen High-Definition Terminal Promotes HD Video Consumption Richer Web Content Challenges Transmission Delay MBB Network Service Waiting Time Promotion Direction Air Interface Bandwidth and RTT together Determine Speed of Content Transmission RTT Content Source Closer to User Helps Reduce RTT Appendix Qualitative Analysis of the Relationship between the TCP Transmission Speed and RTT Quantitative Analysis of Air Interface Bandwidth and RTT Requirement at Video Initial Buffering Stage Page Loading Time and Quantitative Analysis for Air Interface Bandwidth and RTT Required... 17

3 Figure Figure Figure 2-1 Traffic Survey... 2 Figure 2-2 Influence Factors Survey... 2 Figure 2-3 Experimental Principle... 5 Figure 2-4 Visual Tracking Technology... 6 Figure 2-5 Patiently Waiting Time Statistics... 7 Figure 3-1 3G network Survey Statistics... 2 Figure 3-2 4G network Survey Statistics... 2 Figure 4-1 End-to-End RTT... 5 Figure 4-2 Bandwidth Requirements in Different Stages... 8 Figure 4-3 Video Resolution Development Trends... 9 Figure 4-4 Web Development Trends Figure 5-1 China Different Region RTT Comparison Figure 5-2 Deploy Cache/CDN to Decrease RTT Figure 6-1 TCP Slow Start Stage Schematic... 16

4 Table Table Table 4-1 Statistical Result... 6 Table 4-2 Bandwidth Requirement in Different Stages... 7 Table 5-1 Air Interface Bandwidth and RTT Required for Different Resolution Video Table 5-2 Air Interface Bandwidth and RTT Required for Different Size Web Page Table 6-1 TCP Slow Start Stage Data Transmit Summary... 18

5 1 Introduction 1 Introduction 1.1 Key Findings User experience in MBB era is mainly the experience of human-to-machine interaction. The most critical indicator of user experience is the waiting time when using OTT service. Network construction goal in MBB era is to build a network with excellent user experience, and the measurable standard is the service waiting time. mlab s study shows that service waiting time with excellent user experience is in about 3 seconds. The experience to achieve service waiting time less than 3 seconds is the excellent MBB network experience. The survey found that about 35 percent of the current global network can meet the experience excellent requirements. The growth of content brings challenges to MBB network: higher resolution video, bigger size web. Key measures to reduce waiting time are: Upgrade air interface bandwidth, reduce network end-to-end delay. 1

6 1 Introduction 1.2 Research Methodology MBB user experience key indicators are studied based on latest Human Factor Engineering method, through Eye Movement experiment. Eye Movement experiment is conducted on 2892 experimenters. It uses Eye Sight Tracking technology to analyze and then obtain user experience research results. Basic data of experimenters: respondent s age distributes between years, sex ratio 6: 4. Experimental test is completed in the first half of

7 2 Explorer Excellent MBB Network Experience Indicators 2 Explorer Excellent MBB Netw ork Experience Indicators 2.1 Waiting Time is Key Indicator to Experience in MBB 2G era s service is mainly voice consumption. It is an era of human to human interaction. MBB era s characteristic is mainly man to machine interaction, with diversified content form. Data content consumption gradually replaces the consumption of voice. In MBB era, Video and web browsing are two main businesses, which accounted for 78% of data consumption in developed market. 1

8 2 Explorer Excellent MBB Network Experience Indicators Figure 2-1 Traffic Survey From voice consumption era to data traffic consumption era, what happens to user experience indicators? In the human to human interaction voice consumption era, the key indicator of user experience is call connection rate, call drop rate, handover success rate, as well as voice MOS value etc. In MBB era, due to the application has changed, from the human to human interaction to man to machine interaction, therefore experience indicator need to be redefined. Research finds that: service waiting time is the most critical indicator of man to machine interaction user experience in MBB era. Figure 2-2 Influence Factors Survey Video Service Experience Key Factor Analytics 2

9 2 Explorer Excellent MBB Network Experience Indicators Web Service Experience Key Factor Analytics Among them, for video one of the most critical factors affecting the user experience is "Video initial buffering time", ie the time required from user clicking the play button to the emergence of the first frame; for web the most critical factors affecting the user experience is "page loading time ", refers to the time the user enters the URL to completely display the desired page. Stalling frequency and stalling time when playing video have strong correlation with video initial buffering time, because initial buffering phase has higher requirement to MBB network bandwidth. If initial buffering time can be shortened in the whole network anytime anywhere, stalling frequency and stalling time can also be reduced. 3

10 2 Explorer Excellent MBB Network Experience Indicators In MBB era, the target of network planning and construction is to build a network with excellent user experience, and the standard to measure is service waiting time. This paper will elaborate how long user s patience is, how to set service waiting time standard, what is the requirement to wireless network, and the key measures to reduce waiting time. This paper will also implement the mapping from user experience to technology, and the association from operator s business goals to network construction goals. 2.2 Experimental Study Users Patiently Waiting Time From user triggering OTT service until service beginning to respond, the waiting time during this period is the most critical factor for MBB user experience. In order to ascertain the user patiently waiting time, mlab studied experimentally: wait for the experimenter to click on the video player to watch, then start the timer when click the play button, with a camera to record the state of the experimenter's eye movements (eye movements and pupil size changes). According to the visual behavioral and biological psychology principle, analyzing eye movement data can obtain the experimenter s patiently waiting for service response time. 4

11 2 Explorer Excellent MBB Network Experience Indicators Figure 2-3 Experimental Principle 2.3 Experimental Theory Human Factors Engineering researches the interaction and reasonable combination among human, equipment and environment, so that the design of equipment and environmental systems are suitable for people's physical and psychological characteristics. Eye tracking technology is an important application of Human Factors Engineering in human-computer interaction, visual experience research field. It uses the pupil center cornea reflection technique. In this research camera position is fixed; screen (light source) is in a fixed position; eyeball center position unchanged (see below). Purkinje image s1 absolute position will not change with the rotation of the eyeball, but its position relative to the pupil is constantly changing. As long as the pupil and the Purkinje image real-time position can be located, and the corneal reflex vector can be calculated, the direction of user s sight can be calculated, using 1 Purkinje image--- a bright spot on the cornea of the eyeball, generated by reflection of light entering the pupil on the outer surface of cornea 5

12 2 Explorer Excellent MBB Network Experience Indicators eyeball image and geometric model. With the change of pupil in diameter and rotation eye movement trajectory can be obtained. Experimenter s eye movement data can be recorded by camera: fixation time, changes in the pupil and the trajectory of the pupil. Figure 2-4 Visual Tracking Technology Researching the close relationship between the capacity limits of human perception and the human eye movements, and measuring the change of user s eye movement through sight line tracking device, can get the user's perception tolerable range of psychological reactions. This method relative to other physiological measures such as galvanic skin and sweat glands, etc, has a more accurate figure. The error can be controlled within 5 milliseconds. 2.4 Result Analysis The basic experimental data: the distance between the pupil center to the 6

13 2 Explorer Excellent MBB Network Experience Indicators screen center is 60 cm, and mobile phone screen sizes is 4 inches. According to principles of visual behavior and biological psychology, establishing the corresponding model between eye movement and human psychology and behavior, the human waiting limit can be confirmed according to tester s eye movement trajectory drift. The study finds: within 2 seconds, more than 95% of the experimenter to maintain good attention; 10% after three seconds of the experimenter's attention began to disperse; when the waiting time more than 5 seconds, 70% of the experimenter to maintain good attention; when the waiting time more than 9 seconds, leaving only 20% of the experimenter to maintain good attention. Terminal screen size is associated with human waiting limit: the smaller screen size, the shorter the time to wait patiently. Figure 2-5 Patiently Waiting Time Statistics Based on human factors engineering s study to human-computer interaction and visual experience, according to service waiting time, MBB network can be divided into three different experience levels: excellent network --- user waiting 7

14 2 Explorer Excellent MBB Network Experience Indicators time is less than 3 seconds; good network --- user wait time is less than 5 seconds; acceptable network - - user wait time is less than 8 seconds. 8

15 3 35% Current MBB Network Reaches Excellent Network Experience Requirements 3 35% Current MBB Network R eaches Excellent Network Experienc e Requirements Waiting time sampling test is carried out on typical MBB global network, with the purpose to understand the current network status quo for various video. Experience testers on each network are more than 100 people, with a total of 9130 people, and valid experience data is 9022 copies. Experience test is carried out from April to July G Network Waiting Time Investigation When playing low resolution 360p video sources, 90% of global network can reach excellent waiting time network requirement; when playing medium resolution 480p video sources, only 23% of global network can reach excellent waiting time network requirement. Current 3G network is universally in the overloaded state. Continuing to enhance 3G network capacity and guide users to migrate to 4G network will help to improve the user experience. 1

16 3 35% Current MBB Network Reaches Excellent Network Experience Requirements Figure 3-1 3G network Survey Statistics 3.2 4G Network Waiting Time Investigation When playing medium resolution 480p video sources, 85% of global network can reach excellent waiting time network requirement; when playing high resolution 720p video sources, 49% of global network can reach excellent waiting time network requirement. Given the current LTE network is lightly loaded network, with the growing number of users and mobile content, user experience is likely to face the risk of falling. Figure 3-2 4G network Survey Statistics 2

17 3 35% Current MBB Network Reaches Excellent Network Experience Requirements All in all, about 35% of the global MBB network can achieve excellent network experience requirements, with the continuous improvement of resolution and video content, and continuous increment of user number, MBB network will face greater challenges. 3

18 4 Video and Web Content Development Raises Higher Demands on Network 4 Video and Web Content Development Raises Higher Demands on Network Ultra-high-definition video and high-capacity web are becoming mainstream, so that increasing content will bring greater challenges to MBB. End-to-end user experience becomes the focus of competition concerns. Through in-depth analysis of user waiting time for video service, the impact by the development of video service to MBB network can be found from the user experience angle. 4.1 User Waiting Time Composition for Video Service Take user access to video service as an example, from user clicking on the play button to start playing the video, waiting time experienced by user is shown as: User Waiting Time = Terminal and Server Response Time + Signaling Transmission Time + Video Initial Buffering Time Terminal Response Time refers to the time from terminal receives user request to sending out request to server. It is determined by terminal processing capacity. For example, the response time is about 200ms when mobile phone Huawei P6 accesses to Youku video. If the phone is low processing capability, the response time will be longer. Server Response Time refers to from content 4

19 4 Video and Web Content Development Raises Higher Demands on Network server receives the request to sending out response to terminal. It has an average of 80 ms. Signaling Interaction Time is the time required by some signaling process including the establishment of the video request, generate the video URL, redirection video address. Analyzing the Youku video service establishment process discovers: these steps have sequence, and are separate TCP stream. The required signaling interaction time to request video content is about 6 times end-to-end Round-Trip Time(RTT) between terminal and server. Signaling interaction time required for other video clients are basically similar. Figure 4-1 End-to-End RTT The above each period of time has following different characteristics: Terminal Response Time depends on the user's terminal handling capacity. Wireless Network RTT is the part that the operator can control and optimize. Internet RTT depends on the entire network transmission quality and the deployment location of content servers. Server Response Time depends on the optimization and improvement of the content provider. 5

20 4 Video and Web Content Development Raises Higher Demands on Network Video Initial Buffering Time means that before start playing video, a certain amount of video content needs be cached, then this video can be played. This period of time to download these contents is called video initial buffering time. According to the TCP transmission characteristics statistical analytics about YouTube, Youku and Sohu video service, it can be found that before the video starts playing, the player needs to cache about 8 seconds amount of data. Different video source may be has slightly different amount of cache. That is, within the initial buffering time, the terminal needs to download about 8 seconds amount of video volume content. The analytical result is shown in the following table: Table 4-1 Statistical Result Client Initial Buffering Quantity(Second) 360p 480p 720p 1080p YouTube Youku Sohu The analysis and calculation of the length of the initial buffering time can be seen on following section. 6

21 4 Video and Web Content Development Raises Higher Demands on Network 4.2 Bandwidth Requirement for Different Resolution Video at Initial Buffering Time Experience excellent network requires waiting time should be less than 3 seconds. For quantitative analysis of air interface bandwidth required for different resolution video in the initial buffering time, terminal response time is assumed as 200 ms, and server response time is assumed as 80 ms. If the RTT is 100 ms (signaling interaction time is 600 ms), the initial buffering time is 2120 ms. As a result, within this time, terminal needs to cache 8 seconds initial buffering amount video content. The qualitative and quantitative analysis principles for following section s calculation can be seen on appendix of this paper. After the TCP connection for downloading video content is established, at first TCP connection enters the slow start stage. In slow start stage, the total amount of data download on TCP layer is:,mss is Maximium Segment Size, 1500 Bytes. For video service, N is generally between 6 and 8. When N is equal to 8, the length of slow start stage is N*RTT, and the data download amount is o.38 M Bytes. After the slow start stage finishes, it enters the steady state. The length of steady state is 2120-N*RTT. The bandwidth required for different resolution video at initial buffering time and data download amount are shown in following table: Table 4-2 Bandwidth Requirement in Different Stages Resolution 360p 480p 720p 1080p 4K Average Code Rate

22 4 Video and Web Content Development Raises Higher Demands on Network (Mbps) Codec: H.264 Steady-State Phase Download Amount (MBytes) Initial Buffering Stage Bandwidth (Mbps) Therefore, higher resolution video requires higher air interface bandwidth. After the completion of video buffer phase, video starts to play. In order to play video smoothly, the bandwidth required to play is usually about 1.5 times that the video code rate, far less than bandwidth required in buffering stage. Bandwidth requirement comparison for video service at different stage is shown below: Figure 4-2 Bandwidth Requirements in Different Stages 8

23 4 Video and Web Content Development Raises Higher Demands on Network 4.3 The Popularity of Large-Screen High-Definition Terminal Promotes HD Video Consumption Smart terminal screen size gradual increment becomes a mainstream trend. In September 2014 it is the turning point of the terminal screen. Mainstream terminal manufacturers all have launched large-screen high-definition terminals, such as Note4, Mate7, iphone 6 plus and so on. The development of large-screen terminal promotes high-definition video consumption. A joint investigation by mlab and Sohu video discovers: before 2012 the terminal is mainly 3.5 inches, with 360p video playback content based; 2014 the terminal is mainly 4.5 inches, with 480p and 720p video playback content based; mainstream terminal is expected to reach 5.5 inches screen size and more, video playback 720p and 1080p content will be the mainstream. Figure 4-3 Video Resolution Development Trends 4.4 Richer Web Content Challenges Transmission Delay For the website visited by iphone, to June 2014, page transmission average size on worldwide Top5000 website grow from early KB to 940KB. In the past two years, it has nearly doubled. With the increasing embedded images, video, flash, web page average size to 2016 is expected to exceed 3MB. 9

24 4 Video and Web Content Development Raises Higher Demands on Network Figure 4-4 Web Development Trends 10

25 5 MBB Network Service Waiting Time Promotion Direction 5 MBB Network Service Waiting Time Promotion Direction To analyze service waiting time composition, each part is service waiting time promotion direction. For example, to enhance the processing capability of the terminal, to improve the content server response time both can improve the overall user waiting time. This paper will mainly research the solution how to reduce network delay on wireless network. To upgrade air interface bandwidth is the major means of improving the user experience, while reducing network end to end RTT is another way to improve user experience. 5.1 Air Interface Bandwidth and RTT together Determine Speed of Content Transmission Excellent network requires under less than 3 seconds of waiting time to finish downloading the amount of the initial buffering data required before video is played, or the content of web page. These requirements are summarized into the following formula: 11

26 5 MBB Network Service Waiting Time Promotion Direction The vast majority of applications, such as video and web are based on TCP transmission. It can be seen that shorter waiting times requires greater TCP layer transmission speed. TCP layer transmission speed is jointly decided by air interface bandwidth and RTT (Round Trip Time). The detailed qualitative and quantitative analysis can be seen in the appendix of this paper. The study finds that: There is a correspondence between the air interface bandwidth and RTT, only synchronous upgrading air interface bandwidth and lowering the RTT can effectively improve the transmission speed of the TCP layer, and reduce user waiting time. The formula in appendix calculates the corresponding value of the air interface bandwidth and RTT required to reach 3 seconds waiting time requirement, for different resolution video and web pages of different sizes: Table 5-1 Air Interface Bandwidth and RTT Required for Different Resolution Video Video Source Resolution Air Interface Bandwidth Required End-to-End RTT Required 360p 2 Mbps 100 ms 480p 6 Mbps 80 ms 720p 10 Mbps 60 ms 1080p 24 Mbps 60 ms Table 5-2 Air Interface Bandwidth and RTT Required for Different Size Web Page Web Average Air Interface End-to-End RTT Page Size Embedded Object Number Bandwidth Required Required 12

27 5 MBB Network Service Waiting Time Promotion Direction 500KB 36 7 Mbps 100 ms 1000KB 50 9 Mbps 80 ms 1500KB Mbps 60 ms 5.2 RTT Content Source Closer to User Helps Reduce RTT End-to-end RTT is composed of two parts: wireless network side RTT and Internet side RTT. Wireless network side RTT is substantially fixed: for UMTS, wireless network side RTT is not more than 60ms. LTE network architecture is more flat, so LTE wireless network side RTT is shorter, no more than 40ms. Internet side RTT is determined by the distance of path between the wireless network and service servers. The farther the distance, the more intermediate network node, RTT is greater, ranging between tens of milliseconds to a few hundred milliseconds. For example in China, OTT servers mostly are deployed in the eastern part of Beijing, Shanghai, Guangzhou, and therefore the western city s average RTT is 40-70ms more than eastern cities. Figure 5-1 China Different Region RTT Comparison 13

28 5 MBB Network Service Waiting Time Promotion Direction Thus, to deploy content source in the position closer to the end user can significantly reduce the Internet side RTT. For example, to deploy Cache/CDN in the Gi interface of packet core network can significantly shorten the path distance between wireless network and content server. Figure 5-2 Deploy Cache/CDN to Decrease RTT 14

29 6 Appendix 6 Appendix 6.1 Qualitative Analysis of the Relationship between the TCP Transmission Speed and RTT When the TCP connection is established, in slow start stage, TCP transmission window gradually increase exponentially. In the 1st RTT, 1 MSS(Maximum Segment Size, 1500 Bytes, assuming transmission window starts from 1 MSS) data content is sent. In the Nth RTT, *MSS data content is sent. Therefore, in the slow start stage TCP layer instantaneous transmission speed is: When the TCP layer transmission speed grows to the air interface bandwidth, it will stop growing:. At this time the size of the TCP transmission window will be stabilized. Slow start stage s duration is N * RTT. If the RTT is bigger, slow start stage will be longer, the longer the service waiting time. According to the above formula, when the air interface bandwidth upgrades, RTT should be reduced in order to make TCP transmission speed reaches air interface bandwidth faster to reduce waiting time. 15

30 6 Appendix 6.2 Quantitative Analysis of Air Interface Bandwidth and RTT Requirement at Video Initial Buffering Stage TCP slow start stage diagram: Figure 6-1 TCP Slow Start Stage Schematic Among them is waiting time, and 1.5*RTT is three-way handshake duration when TCP connection is establishing. The amount of data required to download within time at video buffering stage is the area surrounded by above TCP layer transmission speed curve. The area is divided into two parts, the first part is the data downloaded in slow start stage, in each RTT the download amount is *MSS, totally N times. The second part is the amount of data downloaded after TCP download speed reaches air interface bandwidth. So the formula to calculate the area is(assuming no packet loss and retransmission): Content Size + ( (N+1.5)*RTT)*Bandwidth; After TCP Layer Transmit Speed Reach Air Interface Bandwidth: Bandwidth 16

31 6 Appendix Bandwidth refers to the air interface bandwidth required for different resolution video at buffering stage, according to the above formula, for each air interface bandwidth corresponding range of RTT can be quantitatively calculated. 6.3 Page Loading Time and Quantitative Analysis for Air Interface Bandwidth and RTT Required Web page loading time includes the main page loading time, main page parsing time(depending on client performance, subsequent calculations ignore this section s analysis in this paper), embedded objects in page loading time, and page rendering loading time. Home page loading time and embedded objects in page loading time are calculated as following: 1. Main page loading time includes: Main page DNS request delay(can be calculated as 1 RTT), main page TCP establishment delay(1.5rtt), main page loading delay. 2. Object loading delay calculate:( Object DNS delay(if belong to the same host with main file, this delay can be ignored)+tcp establishment delay+object loading cumulative delay) (total number of objects number of objects loading on single TCP number of concurrent TCP). Take about 1 MByte size web page as an example, assume that the main file size is 20kB, there are average 50 embedded objects, average size of an embedded 17

32 6 Appendix object is 20KB. For one web page there are 10 concurrent TCP connections, and each TCP can transmit two objects. During slow start stage, Nth RTT will transmit: *MSS Bytes. The summary is: Table 6-1 TCP Slow Start Stage Data Transmit Summary RTT TCP Transmit In Nth RTT Data From 1 st to Nth RTT Number Window Size Transmit Amount Total Transmit Amount 1st 1*MSS 1.5KB 1.5KB 2nd 2*MSS 3KB 4.5KB 3rd 4*MSS 6KB 10.5KB 4th 8*MSS 12KB 22.5KB 5th 16*MSS 24KB 46.5KB Web page loading time is calculated as following: 1. If during slow start stage initial transmission window is 1 MSS, main page (20KB) and single embedded object(20kb) both need 3.5 RTT to finish the loading procedure. Each TCP connection can load 2 objects, and these 2 objects loading time is: 3.5 RTT(first object loading time) + 1 RTT(Get request) + 1 RTT(second object loading time) = 5.5 RTT. So the web page loading time is: main file loading time(1rtt(dns request)+1.5rtt(tcp establishment)+3.5rtt) + embedded object loading time(1.5rtt(tcp establishment)+5.5rtt+1rtt (TCP connection release time)) * ( ) 26RTT. 2. If during slow start stage initial transmission window is 2 MSS, main page and TCP first object loading time both reduce 1 RTT. So the web page loading time 18

33 6 Appendix is: main file loading time(1rtt+1.5rtt+2.5rtt) + embedded object loading time(1.5rtt+4.5rtt+1rtt) * ( ) 23RTT. According to mlab s statistics, for most of web page the initial transmission window is 2, so the web page loading time is about 23 * RTT. In this paper, web page parsing latency and rendering latency are assumed about 1 second. The total web page displaying time needs to be less than 3seconds, so that 23 * RTT < 2s, then RTT < 80ms. TCP Layer Average Transmission Speed Where the object size is 20KB, transmission time is 4.5 RTT, TCP concurrent connections are

34 6 Appendix 20