In Broadcast - August 2019 - 54

54

www.inbroadcast.com | Vol: 9 - Issue 7 | August 2019

InFile

Performance Monitoring
in ABR Delivery Systems
Jim Welch, Senior Consulting Engineer, Telestream,
argues that monitoring requires much more than simply
evaluating users' experience levels...

M

edia
production
and
distribution companies go
to great lengths to ensure that the
media they create is of the highest
quality - their reputation and
business depends on it. They apply
all kinds of QA metrics to the media
in order to ensure that the end
customer gets the best experience
they can from the final product,
whether it be over-the-air, via cable Figure 1: Adaptive Bit Rate
or satellite, or even to laptops, streaming video delivery
tablets and smart phones.
Clearly, some kind of monitoring
Providers of ABR (Adaptive Bitrate in the delivery chain is needed in
Streaming) content, however, are order to pinpoint and rectify issues
faced with an additional issue - their during (or hopefully before) the actual
content is generally delivered to transmission - and all of the above
the end-user via a content delivery examples were indeed debugged
network (CDN) or even the internet. by analysing metrics derived from a
Issues can (and do) arise as the media monitoring system.
traverses the network. Some realIt is important to note that simply
world examples are:
evaluating a viewer's quality of
*	 During a major sports package experience and service is not enough.
launch,
poor
(unacceptable) We must acquire sufficiently detailed
performance was encountered in many monitoring information at key
players. Why?
locations throughout the delivery
*	 During a sports package launch chain with specific types of metrics in
event, many users of a specific game order to take cost-effective corrective
console were experiencing frequent actions when issues arise.
pauses in the delivered video as their
players buffered incoming media. Why The ABR Media Supply Chain
was that?
Adaptive bit rate video streaming
*	 A CDN vendor reports that end- over HTTP uses multiple copies of the
user issues were caused by excessively same material, encoded to different
long response time from the supplier's bit rates, which are then sliced
origin server. Is that claim valid?
into small files, or segments, each

Figure 2: Representative end-to-end monitoring metrics and monitoring locations

holding typically two to 10 seconds
of displayed video. These chunks are
then commonly published to origin
servers that typically reside within a
CDN and transmitted to caching and,
ultimately, edge servers. The end
user's client player requests each
segment in succession from an edge
server in order to play back the media.
To do this, the player must also be
presented with a playlist or manifest
which details the locations of each
of the segments - there are therefore
several manifests, each pointing at the
segments for a specific bit rate variant.
If a client-viewing device cannot
get chunks fast enough for a highquality, high-bit-rate stream, it
dynamically and seamlessly starts to
request chunks from a lower-quality,
lower-bit-rate stream to display
uninterrupted video. Of course, this
requires that each segment of each
variant is perfectly time-aligned, or
the viewer will be able
to see discontinuities
when the switch to
a different bit rate
happens. Note that the
switch is bidirectional
- if the delivery bit
rate improves, the
player will switch up
to a higher bit rate
version. This behaviour
can make provisioning
a CDN more difficult:
adding more bandwidth
won't necessarily result
in more clients having
access - the existing
players might all detect

the extra bandwidth and switch to
higher bit rate variants!
Note here, though, that network
performance (not just bandwidth)
plays a key role in viewer satisfaction.
During playback, the player must
request for the next chunk before
the current chunk has completed
playout. The network must deliver
the request, and the server must
issue a timely response to this
request. The network must then
deliver the requested chunk fast
enough to the player and the player
must successfully queue the chunk
to permit seamless playout to the
viewer.
Figure 1 shows the architecture
overview.
What's Old Is New Again
The fundamental principle for
monitoring ABR delivery networks
is by no means new - you deploy
monitoring
systems
throughout
the delivery network and report
the metrics found back to a central
console,
which
displays
that
information to an operator who, if
necessary, takes corrective action.
This is how we have performed system
monitoring and fault finding in systems
for years - you would use several scope
probes, connected to an oscilloscope,
in order to define the point at which
the signal failed. This approach is
equally applicable to the ABR delivery
chain - it just takes a different central
reporting system and different types of
probes.
Standards and
Recommended Practices
Measuring on its own doesn't provide
a picture of system performance - you
need to know which standards you
are measuring to. There are several
standards and recommended practices
used to benchmark ABR delivery, such
as:
*	 ANSI/SCTE
168-6
2017,
"Recommended
Practice
for
Monitoring Multimedia Distribution
Quality". This describes the basic
principle of using multiple, timesynchronised probes at several
recommended locations to identify and
report metrics in order to pinpoint the
cause of a fault. The timestamping


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In Broadcast - August 2019

Table of Contents for the Digital Edition of In Broadcast - August 2019

Contents
In Broadcast - August 2019 - Intro
In Broadcast - August 2019 - Cover1
In Broadcast - August 2019 - Cover2
In Broadcast - August 2019 - Contents
In Broadcast - August 2019 - 4
In Broadcast - August 2019 - 5
In Broadcast - August 2019 - 6
In Broadcast - August 2019 - 7
In Broadcast - August 2019 - 8
In Broadcast - August 2019 - 9
In Broadcast - August 2019 - 10
In Broadcast - August 2019 - 11
In Broadcast - August 2019 - 12
In Broadcast - August 2019 - 13
In Broadcast - August 2019 - 14
In Broadcast - August 2019 - 15
In Broadcast - August 2019 - 16
In Broadcast - August 2019 - 17
In Broadcast - August 2019 - 18
In Broadcast - August 2019 - 19
In Broadcast - August 2019 - 20
In Broadcast - August 2019 - 21
In Broadcast - August 2019 - 22
In Broadcast - August 2019 - 23
In Broadcast - August 2019 - 24
In Broadcast - August 2019 - 25
In Broadcast - August 2019 - 26
In Broadcast - August 2019 - 27
In Broadcast - August 2019 - 28
In Broadcast - August 2019 - 29
In Broadcast - August 2019 - 30
In Broadcast - August 2019 - 31
In Broadcast - August 2019 - 32
In Broadcast - August 2019 - 33
In Broadcast - August 2019 - 34
In Broadcast - August 2019 - 35
In Broadcast - August 2019 - 36
In Broadcast - August 2019 - 37
In Broadcast - August 2019 - 38
In Broadcast - August 2019 - 39
In Broadcast - August 2019 - 40
In Broadcast - August 2019 - 41
In Broadcast - August 2019 - 42
In Broadcast - August 2019 - 43
In Broadcast - August 2019 - 44
In Broadcast - August 2019 - 45
In Broadcast - August 2019 - 46
In Broadcast - August 2019 - 47
In Broadcast - August 2019 - 48
In Broadcast - August 2019 - 49
In Broadcast - August 2019 - 50
In Broadcast - August 2019 - 51
In Broadcast - August 2019 - 52
In Broadcast - August 2019 - 53
In Broadcast - August 2019 - 54
In Broadcast - August 2019 - 55
In Broadcast - August 2019 - 56
In Broadcast - August 2019 - 57
In Broadcast - August 2019 - 58
In Broadcast - August 2019 - 59
In Broadcast - August 2019 - 60
In Broadcast - August 2019 - 61
In Broadcast - August 2019 - 62
In Broadcast - August 2019 - Cover3
In Broadcast - August 2019 - Cover4
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