tektronix_tektronix 28/11/2013 16:50 Page 2
COMPANY CONTRIBUTION
ABR platforms have much in
common because typically they are
deployed using the H.264
compression standard and as a result
it is common to use the same
transcoded content with each of the
operator’s ABR delivery platforms.
Content Delivery
After transcode, each stream is
fragmented into fixed time duration
fragments, the content is encrypted
and Digital Rights Management
(DRM) is applied. The content is now
ready for delivery to subscribers using
a playout device known as an Origin
Server.
The encryption that is a key
element of DRM makes it impossible
for the same level of deep packet
inspection to be performed and QoE
monitoring is impossible at this point.
It can also be argued that as the
content has already been verified
prior to fragmentation and
encryption, this makes checking it
after that process pointless. If the
content is acceptable when it is
encrypted, it is impossible for it not to
be in precisely the same state when it
is decrypted by the subscriber’s
device.
After encryption, operators use
QoS measures to ensure the correct
content delivery of capability of the
Origin Servers and CDN
caching/streaming servers. This is
performed at two points: After
streams leave the origin server (Point
3 in the graphic) and when they leave
content and caching servers, which is
the last step before delivery to end
users’ devices (Point 4 in the graphic).
At these monitoring points, the
focus turns to QoS metrics such as
manifest verification, fragment load
time and latency as well as ensuring
that the various profile bitrates for
each service are as expected. This is
performed by active devices that
emulate requests made by end users
in order to subscribe to all services at
all profiles.
ABR requires precise and
exhaustive tracking of the huge
number of packets that make up the
various services. “When the device
requests a chunk at a specific bit rate
the system needs to check the
manifest file and make sure that it’s
actually the right bit rate that is being
sent,” Robinson said. “If it requests a
fragment at 500 kilobits per second
and for whatever reason it incorrectly
sends video 1 megabit at per
second, the service will fail.”
QoS indeed is vital to the
success of ABR Streaming which
uses HTTP to request each
fragment in the same way that a
web page is requested. This is a
unicast approach in which only
the stream requested is
sent. This puts
pressure on the system
to deliver data in a
precise fashion and,
consequently, puts
more pressure on video
and audio monitoring
and service assurance
techniques. ABR is so
complex that a very
rigid and structured
monitoring
regime must be
in place to
ensure that the
system is functioning
correctly.
In summary,
with ABR
streaming services,
it is important to
monitor both video
and audio QoE both
at ingest and posttranscode for all
available profiles.
After fragmenting
and encryption, it is
important to
monitor the
QoS of the
content
delivery
platform to
ensure that the system delivers
what the client-side player is
expecting to
receive. In
addition, for
systems offering
on-demand
services, it is
important to verify
the decodability of
these assets prior
to being made
available for
transmission. If
operators perform
all these steps, they
will be best placed to
deliver the highest
possible quality video and audio
programming over a robust and
Tektronix Monitoring and QC for
Adaptive Bit Rate Streams
entry, Sentry ABR and Cerify are products within the
Tektronix portfolio which help operators ensure
quality control for their mu