Making Sense Of Bandwidth The NetSense Way by Face To Face Live


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Making Sense Of Bandwidth The NetSense Way by Face To Face Live

  1. 1. Face to Face Live 480.348.3400 www.facetofacelive.comA Radvision / Avaya Expert Partner
  2. 2. White PaperMaking Sense of Bandwidth the NetSense Way Network Congestion in Unmanaged NetworksBandwidth Estimation and Adaptation Techniques RADVISION’s NetSense Technology
  3. 3. White Paper The growing use of video-based applications over the Internet has made bandwidth estimation and adaptation technologies a critical requirement in any visual communications system. RADVISION’s NetSense technology is designed to deliver standardized and optimized video calling over unmanaged networks, enabling a consistently high quality of experience. Applicable to a wide range of end-point devices and a variety of network configurations, NetSense allows visual communications to be implemented across all enterprise and consumer arenas. RADVISION’s integrated approach enables service providers, enterprises, and system integrators to provide their clients with the best user experience possible.ContentsAbstract ................................................................................................................................... 3Challenges of Real-Time Video Calling Over the Internet .......................................................... 3Techniques for Bandwidth Estimation and Adaptation ............................................................... 4The NetSense Algorithm ........................................................................................................... 5NetSense In Action ................................................................................................................... 6NetSense in RADVISION’s End-to-End Solution......................................................................... 6Conclusion ............................................................................................................................... 7 RADVISION WHITE PAPER | 2
  4. 4. White PaperAbstractVideo calling over the Internet is becoming more and more Congestion in IP networks and packet corruption frequentlypopular. The quality of video in such applications is a major occur, leading to delay, jitter and packet loss, which all degradecontributor to the overall user experience. the user experience.Video quality depends heavily on bandwidth availability. If Packet loss can be caused by a number of factors such as:the network path used is either under or over-utilized, high signal degradation over the network due to multi-path fading,quality cannot be achieved. An accurate method for estimating packet drop because of congestion, corrupted packets rejectedavailable bandwidth across a network path and for adapting in transit, faulty network hardware or faulty routing.the bit rate accordingly is therefore very desirable. Network Congestion ExplainedThis white paper presents NetSense, a novel technique developedby RADVISION for dynamic bandwidth estimation and While all of these impairments must be dealt with in order toadaptation designed for real-time, interactive video calling. assure high quality of experience over unmanaged networks, this paper will focus specifically on the problem of networkBy detecting delays in received video frames, NetSense estimates congestion.available network bandwidth and adapts the transmittedbitrate accordingly in order to avoid packet loss. Network congestion arises at overloaded network paths where the bitrate being sent exceeds the path’s maximumSince NetSense uses only standard protocols for delay detection available bandwidth. This results in blocks of data, or packets,and flow control, it can be easily and effectively used with accumulating at bottleneck routers along the path andtraditional visual communications systems. eventually being dropped.NetSense has been shown to efficiently estimate available Packet loss caused by network congestion is usually perceivedbandwidth, outperforming competing tools in terms of both at the receiver side as severe video artifacts and hence candetection time and accuracy. By implementing NetSense in its significantly affect the quality of conferencing solutions, RADVISION ensures superiorvideo calls over unmanaged networks, compared to other Congestion control algorithms, found in most video callingsolutions available in the market today. products, deal with this problem by lowering the bitrates whenever packet loss is detected. However, the packetsChallenges of Real-Time Video Calling Over that are dropped before packet loss is detected and bitrate isthe Internet reduced already introduce a dramatic drop in video quality.Video calling has become one of the Internet’s fastest growing Furthermore, packet loss is not always caused by congestion,phenomena. Millions have discovered that reaching out as explained previously. Reducing the bitrate will thereforeand seeing someone is the next best thing to being there. not solve the problem in all cases.Implemented in many products and form factors, from Another way of dealing with packet loss, found in streamingvideophones to instant messaging and from video conferencing and other non-real-time video solutions, is retransmitting theendpoints to mobile handsets, it has become a major mode missing packets. However, retransmission is not applicableof communicating. for interactive real-time calls due to the latency introducedSince video communication involves the transfer of high by sending feedback from receiver to transmitter and thenbandwidth multimedia data in real-time, ensuring minimal waiting for the retransmitted packets to arrive.delay is critical. As the data is sent over managed networks In short, one of the main challenges in real-time, interactive(such as leased lines) and unmanaged networks (such as the video calling is adapting the bitrate to the path withoutInternet), quality of service (QoS) is not always guaranteed. introducing packet loss. RADVISION WHITE PAPER | 3
  5. 5. White PaperChanges in Effective Bandwidth Another scenario, as depicted in figure 2 above: You could be in your home office making a video call over a 2MbpsChanges in effective bandwidth occur even if the line has a DSL line, when your e-mail client starts to synchronize withguaranteed bandwidth, and even with leased lines. This is the server at headquarters. Again, bandwidth will be reducedbecause the various applications on different devices consume until the e-mail client has done synchronizing and then willvariable amounts of bandwidth. increase again. The challenges for any bandwidth estimation and adaptation technique include dealing with such fluctuations in bandwidth, adapting quickly and efficiently to the effective bandwidth at any given time and preventing packet loss during these changes in bandwidth. Techniques for Bandwidth Estimation and Adaptation The subject of bandwidth estimation and adaptation for communications over unmanaged networks is not new. In fact there has been a lot of research and development in this field in recent years. However, many of the algorithms found in non real-time applications cannot be used by video calling systems because Fig. 1: MPLS connection between remote branch and HQ they lack the characteristics discussed hereunder.For example, an MPLS line of 10Mbps in a small branch The Characteristics of Video Callingoffice, as depicted in figure 1 above, would easily support Video streams are made up of video frames, each compriseda single video call between this office and headquarters; of a set of packets that are transmitted to the network athowever, more people from that office connecting at the approximately the same time. These packets have to besame time would reduce the effective bandwidth, making treated as such in any bandwidth estimation calling more difficult. Video streams usually have a strongly obeyed structure (known as GOP or Group of Pictures), and different frames in the GOP have different significance. Any viable solution must take this into consideration. There are also bitrate fluctuations in real-time video calling that have to be modeled and compensated for in a bandwidth estimation algorithm. Finally, and most importantly, video calling is very standardized in nature. It relies completely on existing protocols that strictly define the communication between sender and receiver. For an algorithm to be both vendor and protocol agnostic, it has to comply with these standards. Standard protocols, for instance, define the communication means between sender and receiver and determine how Fig. 2: DSL connection between home office and HQ. commands and feedback are sent in a video call. Flow control commands, designed to alert the sender to change the bandwidth, are sent by the receiver according to these standards. In most cases the sender does not have any other control mechanism for bandwidth management. RADVISION WHITE PAPER | 4
  6. 6. White PaperExisting Bandwidth Estimation Techniques case, the packets are usually stored by network router(s) in a buffer until processing is complete. This introduces a delay inExisting bandwidth estimation techniques generally fall into packet arrival at the receiver end, known as queuing delay. Thethree categories: algorithms that are designed for specific queuing delay is proportional to the router’s buffer size.networks, usually with guaranteed QoS; algorithms that use“probing” packets to evaluate bandwidth at the beginning Packet loss occurs when the buffer overflows, i.e., when theof the call; and algorithms targeting video streaming, where buffer has no room to store further arriving packets. In mosta client-server model is assumed. routers, packet loss can occur even earlier, as these routers randomly drop packets to reduce bandwidth when queuingMost video calling solutions rely on a packet loss-based delay is accumulated.algorithm, where a flow control command reduces thebandwidth being transmitted as soon as packet loss is perceived Figure 3 shows the delay and packet loss patterns obtainedon the receiver side. There are several methods of reducing with nearly 50% over-utilization of available bandwidth. Inand then converging bandwidth, but most are “cautious” this case, a 2Mbps video is transmitted over an MPLS linein nature; they do not attempt to reach the true effective with a 1.4Mpbs limit. The blue line represents the delay inbandwidth but rather settle for a rough, lower estimation. frame arrival at the receiver side. The orange dots represent packet loss events, with every dot corresponding to lossThe NetSense Algorithm of one or more consecutive packets. Note that the delayNetSense was developed with unmanaged networks in mind, accumulates during 2/3 of a second (or 19 video frames)specifically the public Internet. Furthermore, it is designed to before the first packet is with real-time video calling, and so complies with thechallenges defined in the relevant section. Effect of Bandwidth Over-UtilizationRADVISION’s algorithm converges to the available bandwidth 300 Delay (miliseconds)in a given path during call setup, and dynamically adjuststo mid-call changes in available bandwidth. It therefore 200perfectly fits the needs of a video calling system on thepublic Internet. 100NetSense’s logic and decisions are executed only at the receiver 0side. As its name suggests, it senses significant increase ordecrease trends in the delay of incoming video frames, and 1 2 3 4 5 6reacts accordingly. Time (seconds)NetSense is delay based. It monitors the delay between senderand receiver, thereby detecting over utilization of the path Fig. 3: Delay and packet losses as perceived at the receiver side during over-before packet loss occurs. utilization of bandwidth.Furthermore, NetSense converges quickly and as closely as Similar setups substantiated the expected results: The receiverpossible to the effective bandwidth. This means you can perceives accumulated delay for a significant period of timemake the most of the available bandwidth, without sacrificing before the first packet is lost. As packet loss tremendouslyquality of experience. reduces video quality, identifying bandwidth over-utilizationDelay Detection at the delay accumulation stage before packets are lost and reducing the transmitted bitrate accordingly is highlyA clear understanding of how bandwidth over-utilization is desirable.experienced at the receiver side is essential for designing abandwidth estimation tool that delivers best possible quality Note that NetSense models the one-way delay between theof experience. sender and the receiver in a way that is agnostic to clock drifts. This makes NetSense applicable to any type of device, fromWhen available bandwidth is over-utilized, packets enter the embedded infrastructure to desktop and mobile handsets.path at a rate faster than the network can process them. In this RADVISION WHITE PAPER | 5
  7. 7. White PaperAlgorithm Flow NetSense In ActionThe NetSense bandwidth estimation algorithm has two modes Due to its unique features and compliance with communicationof operation: At call initiation it scans the range of possible standards, NetSense works optimally in various networkbitrates, and quickly but effectively converges to the precise conditions, over different network links (MPLS, ADSL, cable)available bandwidth. During the call, it detects changes in the and with different vendors.available bitrate, adapting the bandwidth accordingly. In real-life scenarios consisting of RADVISION videoThe algorithm supports the common scenario of multiple conferencing equipment with NetSense inside, as well ascalls running over the same line, sharing the bandwidth, and when connecting to equipment from leading vendors such asassists in assuring fairness in bandwidth consumption. Figure LifeSize (now Logitech), Polycom and Tandberg (now Cisco),4 depicts an example of such scenario: NetSense proved to be a vital component and to significantly enhance the quality of experience. NetSense is superior to other solutions in regards to convergence Convergence of a Multiple Call Scenario time - both for call initiation and response to mid-call changes 600000 in the available bandwidth. It converges to 90-95% of the available bandwidth in up to 15 seconds with no packet 500000 loss at all and an average detection time of 9.65 frames. In other words, when the bandwidth is over-utilized, NetSense Bandwidth 400000 takes only 9.65 frames, or less than a 1/3 of a second, to detect it. 300000 NetSense in RADVISION’s End-to-End 200000 Solution 100000 NetSense technology will be implemented across RADVISION’s entire product range, starting with the release of SCOPIA v7.5 0 and the BEEHD client framework. This will include RADVISION’s 5 10 15 20 software clients (SCOPIA Desktop and BeeHD for desktop), Time (seconds) endpoints (VC240 and XT1000) and the Elite MCU. With this new technology, RADVISION offers the highest 1st call 2nd call quality of experience even over unmanaged networks, specifically in these use cases: Fig. 4: Convergence of 2 calls sharing the same line • Point-to-point calling. The solution ensures high quality of experience, even if network conditions and/or availableThe above setup of an MPLS line, with a bandwidth limit bandwidths are limited.of 850Kbps and a significant roundtrip delay of 700-800 • Remote calling, such as when tele-workers call into themilliseconds, shows how the NetSense algorithm enables company network. The RADVISION offering enables amultiple video calls to share the same connection and stabilize high quality call, even if the home connection suffersthe use of their shared bandwidth in an as close to optimal from limited bandwidth or low quality network.manner as possible. • Virtual MCU deployments, where MCUs are deployedThe 1st call was initiated with with a bitrate of 500Kbps, in different geographic locations (branches) and arewhile the 2nd call was initiated with a bitrate of 300Kbps. connected over dedicated lines or the public Internet. TheNetSense attempts to optimize the bandwidth utilization of solution enables a perfect connection between networkboth calls, resulting finally (after around 15 seconds) in the elements, even if the paths are limited.2 calls converging to 450Kbps and 375Kbps. In addition to its infrastructure products powered by NetSense, RADVISION will soon introduce NetSense as part of the unique SDK it offers vendors who wish to deploy a ready- made video calling engine within their products. RADVISION WHITE PAPER | 6
  8. 8. White PaperConclusionBandwidth estimation and adaptation techniques are truly amust for any video-based application that utilizes the Internetfor communications.RADVISION’s NetSense technology is focused on providingstandardized and optimized video calling over the Internet.It enables consistently high quality visual communications,even over unmanaged networks, across all enterprise andconsumer arenas.The RADVISION solution delivers an optimized videoexperience, transmittable to a wide range of end pointdevices, on a variety of network configurations. This integratedapproach enables service providers, enterprises and systemintegrators to provide a high quality user experience.With effective bandwidth adaptation dramatically improvingthe video experience, NetSense brings substantial benefitto users while maintaining the high level of interoperabilityRADVISION is known for. MKT-DI-231110-01 About RADVISION RADVISION (NASDAQ: RVSN) is the industry’s leading provider of market-proven products and technologies for unified visual communications over IP and 3G networks. With its complete set of standards-based video communications solutions and developer toolkits for voice, video, data and wireless communications, RADVISION is driving the unified communications evolution by combining the power of video, voice, data and wireless – for high definition video conferencing systems, innovative converged mobile services, and highly scalable video-enabled desktop platforms on IP, 3G and emerging next-generation networks. For more information about RADVISION, visit USA/Americas EMEA APAC T +1 201 689 6300 T +44 20 3178 8685 T +852 3472 4388 F +1 201 689 6301 F +44 20 3178 5717 F +852 2801 4071 This document is not part of a contract of license as may be expressly agreed RADVISION is registered trademarks of RADVISION, Ltd. All trademarks recognized. All rights reserved © 2010 RADVISION, Ltd. Rev D 07-10.