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

1. Face to Face Live
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2. White Paper
Making Sense of Bandwidth
the NetSense Way
Network Congestion in Unmanaged Networks
Bandwidth Estimation and Adaptation Techniques
RADVISION’s NetSense Technology

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.
Contents
Abstract ................................................................................................................................... 3
Challenges of Real-Time Video Calling Over the Internet .......................................................... 3
Techniques for Bandwidth Estimation and Adaptation ............................................................... 4
The NetSense Algorithm ........................................................................................................... 5
NetSense In Action ................................................................................................................... 6
NetSense in RADVISION’s End-to-End Solution......................................................................... 6
Conclusion ............................................................................................................................... 7
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4. White Paper
Abstract
Video calling over the Internet is becoming more and more Congestion in IP networks and packet corruption frequently
popular. The quality of video in such applications is a major occur, leading to delay, jitter and packet loss, which all degrade
contributor 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 rejected
available 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 Explained
This white paper presents NetSense, a novel technique developed
by RADVISION for dynamic bandwidth estimation and While all of these impairments must be dealt with in order to
adaptation designed for real-time, interactive video calling. assure high quality of experience over unmanaged networks,
this paper will focus specifically on the problem of network
By detecting delays in received video frames, NetSense estimates congestion.
available network bandwidth and adapts the transmitted
bitrate accordingly in order to avoid packet loss. Network congestion arises at overloaded network paths
where the bitrate being sent exceeds the path’s maximum
Since 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 and
traditional visual communications systems. eventually being dropped.
NetSense has been shown to efficiently estimate available Packet loss caused by network congestion is usually perceived
bandwidth, outperforming competing tools in terms of both at the receiver side as severe video artifacts and hence can
detection time and accuracy. By implementing NetSense in its significantly affect the quality of experience.
video conferencing solutions, RADVISION ensures superior
video calls over unmanaged networks, compared to other Congestion control algorithms, found in most video calling
solutions available in the market today. products, deal with this problem by lowering the bitrates
whenever packet loss is detected. However, the packets
Challenges of Real-Time Video Calling Over that are dropped before packet loss is detected and bitrate is
the 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 therefore
and 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 streaming
videophones to instant messaging and from video conferencing and other non-real-time video solutions, is retransmitting the
endpoints to mobile handsets, it has become a major mode missing packets. However, retransmission is not applicable
of communicating. for interactive real-time calls due to the latency introduced
Since video communication involves the transfer of high by sending feedback from receiver to transmitter and then
bandwidth 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 without
Internet), quality of service (QoS) is not always guaranteed. introducing packet loss.
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5. White Paper
Changes in Effective Bandwidth Another scenario, as depicted in figure 2 above: You could
be in your home office making a video call over a 2Mbps
Changes in effective bandwidth occur even if the line has a DSL line, when your e-mail client starts to synchronize with
guaranteed bandwidth, and even with leased lines. This is the server at headquarters. Again, bandwidth will be reduced
because the various applications on different devices consume until the e-mail client has done synchronizing and then will
variable 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 Calling
office, as depicted in figure 1 above, would easily support Video streams are made up of video frames, each comprised
a single video call between this office and headquarters; of a set of packets that are transmitted to the network at
however, more people from that office connecting at the approximately the same time. These packets have to be
same time would reduce the effective bandwidth, making treated as such in any bandwidth estimation solution.
video 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.
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6. White Paper
Existing Bandwidth Estimation Techniques case, the packets are usually stored by network router(s) in a
buffer until processing is complete. This introduces a delay in
Existing bandwidth estimation techniques generally fall into packet arrival at the receiver end, known as queuing delay. The
three 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 the
of the call; and algorithms targeting video streaming, where buffer has no room to store further arriving packets. In most
a client-server model is assumed. routers, packet loss can occur even earlier, as these routers
randomly drop packets to reduce bandwidth when queuing
Most video calling solutions rely on a packet loss-based delay is accumulated.
algorithm, where a flow control command reduces the
bandwidth being transmitted as soon as packet loss is perceived Figure 3 shows the delay and packet loss patterns obtained
on the receiver side. There are several methods of reducing with nearly 50% over-utilization of available bandwidth. In
and then converging bandwidth, but most are “cautious” this case, a 2Mbps video is transmitted over an MPLS line
in nature; they do not attempt to reach the true effective with a 1.4Mpbs limit. The blue line represents the delay in
bandwidth 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 loss
The NetSense Algorithm of one or more consecutive packets. Note that the delay
NetSense 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 lost.
deal with real-time video calling, and so complies with the
challenges defined in the relevant section. Effect of Bandwidth Over-Utilization
RADVISION’s algorithm converges to the available bandwidth
300
Delay (miliseconds)
in a given path during call setup, and dynamically adjusts
to mid-call changes in available bandwidth. It therefore
200
perfectly fits the needs of a video calling system on the
public Internet. 100
NetSense’s logic and decisions are executed only at the receiver
0
side. As its name suggests, it senses significant increase or
decrease trends in the delay of incoming video frames, and 1 2 3 4 5 6
reacts accordingly. Time (seconds)
NetSense is delay based. It monitors the delay between sender
and 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 receiver
possible to the effective bandwidth. This means you can
perceives accumulated delay for a significant period of time
make the most of the available bandwidth, without sacrificing
before the first packet is lost. As packet loss tremendously
quality of experience.
reduces video quality, identifying bandwidth over-utilization
Delay Detection at the delay accumulation stage before packets are lost
and reducing the transmitted bitrate accordingly is highly
A clear understanding of how bandwidth over-utilization is desirable.
experienced at the receiver side is essential for designing a
bandwidth estimation tool that delivers best possible quality Note that NetSense models the one-way delay between the
of experience. sender and the receiver in a way that is agnostic to clock drifts.
This makes NetSense applicable to any type of device, from
When 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
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7. White Paper
Algorithm Flow NetSense In Action
The NetSense bandwidth estimation algorithm has two modes Due to its unique features and compliance with communication
of operation: At call initiation it scans the range of possible standards, NetSense works optimally in various network
bitrates, 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 video
The algorithm supports the common scenario of multiple conferencing equipment with NetSense inside, as well as
calls running over the same line, sharing the bandwidth, and when connecting to equipment from leading vendors such as
assists 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 available
The 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 the
milliseconds, shows how the NetSense algorithm enables company network. The RADVISION offering enables a
multiple video calls to share the same connection and stabilize high quality call, even if the home connection suffers
the 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 deployed
The 1st call was initiated with with a bitrate of 500Kbps, in different geographic locations (branches) and are
while the 2nd call was initiated with a bitrate of 300Kbps. connected over dedicated lines or the public Internet. The
NetSense attempts to optimize the bandwidth utilization of solution enables a perfect connection between network
both 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.
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8. White Paper
Conclusion
Bandwidth estimation and adaptation techniques are truly a
must for any video-based application that utilizes the Internet
for communications.
RADVISION’s NetSense technology is focused on providing
standardized and optimized video calling over the Internet.
It enables consistently high quality visual communications,
even over unmanaged networks, across all enterprise and
consumer arenas.
The RADVISION solution delivers an optimized video
experience, transmittable to a wide range of end point
devices, on a variety of network configurations. This integrated
approach enables service providers, enterprises and system
integrators to provide a high quality user experience.
With effective bandwidth adaptation dramatically improving
the video experience, NetSense brings substantial benefit
to users while maintaining the high level of interoperability
RADVISION 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 www.radvision.com
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