Testing IPTV Channel
IPTV channel zapping is a key element of the user's QoE
(Quality of Experience). Agilent N2X provides the most
accurate and reliable channel zapping test solution that
helps service providers and network equipment
manufacturers evaluate if network equipment is ready
to enable"Multiplay" services.
Testing IPTV Channel Zapping
Introduction However, offering a competitive TV
service over an IP network is challenging
Agilent N2X the infrastructure of CSPs network,
especially access network. A standard
Agilent N2X is the industry's most
IPTV channel using MPEG-2 encoding
comprehensive test solution for testing
requires 3.5Mbps. If the service providers
the development and deployment of
allow 2~3 channels per household and
network services for converging network
have other network services running on
infrastructures. Service providers,
the same physical connection, the
network equipment manufacturers
minimal requirement of access bandwidth
(NEMs), and component manufacturers
will be at least 10Mbps or higher.
can verify service attributes of entire
networks end-to-end, while also isolating Before rolling out a new B-RAS
problems down to individual networking (Broadband Remote Access Server), EAR
devices and subsystems. (Ethernet Aggregation Router), or
IP/Ethernet-based DSLAM (Digital
Subscriber Line Access Multiplexer) in the
IPTV access/edge network, thorough tests are
Internet Protocol Television (IPTV) required to make sure there is no barrier
services, are being rolled out at an for achieving better QoE of IPTV service.
unprecedented rate as a key component of
service providers' "Multiplay" service
offerings. These new services are
expected to yield additional profits for
Communication Service Providers (CSP)
and allow increased competition in the
television industry. The expectation of
customers are high and the "quality of
experience (QoE)" they receive from their
IPTV service will be paramount.
"Multiplay" services, especially video
services, are driving CSPs to upgrade to
the next generation access network.
Considering the huge investment and
competition from Cable companies, CSPs
cannot afford a service failure.
Testing IPTV Channel Zapping
IPTV Channel Zapping When they change to another channel,
they just leave the group and join the new
In addition to the bandwidth challenge, a one. Technically, the network delay of
key element of QoE for IPTV is the delay in channel zapping is mainly influenced by
changing channels - how long does it take IGMP join/leave delay that can be
to change from one channel to another? regarded as control plane performance of
Does the customer get the right channel? IGMP.
If customers change channels in rapid
succession, is the delay worse? What Multicast protocols have been around for
about if the network grows (more years but were rarely used in the
channels or more subscribers)? How are traditional Internet infrastructure.
channel change times impacted by Unpredictable multicast performance of
background unicast (VoIP or High-Speed network equipment becomes a serious
Internet) traffic? barrier that slow down successful IPTV
service delivery. Nowadays, some routers
These are questions that service providers are still forwarding multicast packets by
planning to offer IPTV services need to ask CPU other than hardware. Most ATM
as they evaluate network equipment. based DSLAMs cannot support multicast
Changing IPTV channels will trigger a replication or lack of related multicast
series of actions within network functions, such as IGMP snooping, IGMP
equipment. Zapping delay is generated by proxy.
both the network and the Set-Top Box Even further, the IPTV services completely
(STB). The N2X solution focuses on the change the ratio of unicast traffic and
measurement of network delay. multicast traffic in the networks. The
Multicast is one of the key technologies video delivery network must handle
that enable the IPTV services. Each multicast efficiently, both data and control
multicast group represents a TV channel. plane.
If there are thousands of users watching To meet the QoE requirements of IPTV
IPTV at the same time, it's not necessary services, network equipment developers
for the B-RAS and DSLAM to carry need to test their equipment to ensure the
thousands of IPTV steams. The users channel "zapping" delays are adequate to
watching a channel are included in a deliver the right service quality for service
multicast group. providers, and finally for end users.
500-1000 Ethernet or ATM IP/MPLS Core
subs Aggregation Network
IGMP IGMP PIM-SM/SSM
n <= N N <= M M Multicast
Multicast video Multicast video video streams
Figure 1: Typical IPTV over DSL network Multicast model
Testing IPTV Channel Zapping
Test Challenges of IPTV Service providers and content providers
may use a range of encoding technologies,
Channel Zapping depending on the nature of the content
IGMP join and leave delay is the key focus (Standard Definition or High Definition),
of IPTV channel zapping measurement. the bandwidth available in the network,
But the ideal test solution for IPTV and other factors. MPEG-2 (SD or HD),
channel zapping is much more than a MPEG-4 AVC (H.264), and Microsoft
simple IGMP join/leave emulation. CSPs Windows Media 9 are all commonly used.
and NEMs have to solve a series of test Thus, the test solution has to be capable
challenges when they are trying to verify of emulating a range of video traffic
the QoE of channel zapping. profiles.
To emulate the user behavior in a testing
1. Accuracy and repeatability
environment as close as reality, the test
A channel zapping action will involve solution needs to support "multiple
several network elements, while channels per household/subscriber" and
acceptable QoE requires the delay through all the users changing channels at a time"
a single device should be no more than that always happens when TV
100 msec. Accurate and repeatable commercials begin.
measurement of every single device as
well as the whole network will help the 3. Scalability and reliability
service provider isolate problems and The scale of the next generation access
avoid 'finger-pointing' issues among network is expending rapidly. A DSLAM is
equipment vendors. physically accessing hundreds of
Accuracy and repeatability brings subscribers. After being aggregated by the
challenges to the testing equipment. Most Ethernet or ATM switched network, a
network performance testers use a B-RAS has to consolidate the traffic of a
"hardware timestamp" in the data plane dozen or more DSLAMs. To provide
packets for latency measurement. But the competitive IPTV content, service
control plane packets normally don't carry providers need to offer more than 100
a "hardware time stamp". Consequently, channels for customers to choose. As a
the timing of control plane packets has to result, the IPTV channel zapping test bed
be handled by the CPU of the tester rather has to emulate 1000s of subscribers and
than hardware. The accuracy of CPU 100s of channels in a test scenario to be
based IGMP join/leave measurement is truly stressful and scalable.
only in the range of 10s of ms. Considering Another scalability issue concerns
the error overlapping of all the DUTs, hardware. The port count and port density
obviously, the error is too big to have true in the access network is increasing rapidly
evaluation of IPTV channel zapping time. nowadays. A fully loaded B-RAS will have
dozens of hardware interfaces. As for the
2. Realistic user environment
DSLAM or aggregation switch, the
emulation number of ports will be more than 100s.
In a realistic 'Multiplay' user environment, Accordingly, the test bed has to support
multiple network protocols like PPPoE and equivalent port numbers and enable all the
DHCP, as well as unicast and multicast test capability in each interface.
user traffic are running simultaneously. Reliability of the test bed is a critical issue.
Background protocol/traffic emulation 'Long Duration service verification, 1000s
will help create a realistic test of subscribers running both unicast and
environment for "channel zapping" multicast traffic, subscribers' traffic and
measurements. protocol flapping, multiple protocols
running simultaneously, etc", all the test
challenges build up a big challenge of
reliability to the tester itself.
Testing IPTV Channel Zapping
4. Full Coverage of related testing Testing IPTV Channel
functionality Zapping using N2X
To fully test the performance and The N2X IPTV Channel Zapping solution
functionality of the SUTs for IPTV channel offers service providers and equipment
zapping, the test solution has to cover all manufacturers a powerful application to
the related protocols. IGMP snooping or accurately validate the channel zapping
proxy, which are used to optimize the performance of broadband access
multicast bandwidth in the network, has equipment under real-world conditions.
to be tested. The full coverage of hardware interface
Hardware coverage is another important and network protocols enables the most
issue of the test solution. Fast Ethernet, scalable and stressful test environment if
Gigabit Ethernet and OC3c/12c ATM are channel zapping.
the most widely used hardware interfaces Moreover, the solution adopts an easy to
in the access network. Some high-end user GUI and easy to understand result
B-RASs devices have also introduced 10 report. Test engineers will easily setup a
Gigabit interfaces. All hardware interfaces complicate test scenario in a couple of
have to be tested. minutes and get a well organized test
report with diagram after the test finished.
Figure 2 shows a simplified network test
scenario of IPTV channel zapping. Agilent
N2X is emulating both the content
provider and subscribers of IPTV service.
The SUT(System Under Test) can be either
a single network element such as B-RAS,
IP DSLAM or a network system combined
by B-RAS, DSLAM, Ethernet/ATM
IPTV Channel Zapping
N2X Test Port 1 System N2X Test Port 2
Under Test DSLAM
Video On Demand DSLAM
N2X Test Port n
Content Provider Access Provider Subscribers
Figure 2: IPTV Channel Zapping
Testing IPTV Channel Zapping
Features Run IGMP, PPPoX, and DHCP
sessions along with multicast &
Accurate hardware timestamping unicast traffic, all simultaneously
of both protocol emulation and on the same test port
traffic packets to 0.1 msec
Today's converged networks are not used
resolution for a single service as in the past. The
When performing any measurement, it is norm is becoming "Multiplay", where
important to have both accuracy and IPTV, VoIP and High-speed Internet
repeatability, so you can be confident that services are all offered on the same
your measurement truly reflects the subscriber connection. For this reason, it
performance of the DUT. Agilent N2X has is important to have background traffic in
unique hardware capabilities that allow the test scenario to determine the impact
the system to timestamp the protocol of this traffic on the channel zapping
emulation (IGMP) packets and multicast performance of your DUT. N2X allows you
traffic packets in real time and at high to run background unicast traffic and
speed. Similarly, our state-of-the-art FPGA other protocol emulations such as PPPoX
technologies allow us to perform highly and DHCP, to realistically determine the
accurate measurements in real-time, performance of your system with mixed
without relying on data capture and services.
post-processing like other solutions on
the market. Channel "flapping" per subscriber
In a real-world network, each user will
Measure channel zapping time on change channels with different patterns. It
a per-subscriber or per-channel is important to be able to test according to
basis different subscriber profiles and to test
It is important to measure the DUT's under different 'stress'conditions.
contribution to the zap time for each For example, what if a large number of
subscriber and each channel, not just the subscribers all change to the same
aggregate performance of the device. N2X channel, such as at the beginning of a
provides IGMP join, IGMP leave, and popular sports match? N2X allows you to
IGMP leave to join delay (channel zapping) configure channel 'flapping' profiles for all
measurements for each simulated the subscribers in your test, and thus
subscriber (IGMP host) and for each simulate many real world scenarios in
channel (multicast group) and presents your testing.
those results in tabular and graphical
Scales to 100s of TV channels and
1000s of subscribers
To adequately characterize the channel
zapping performance of your DUT, it is
important to test under scaled conditions.
Scaling the number of subscribers as well
as the number of channels in the network
are both critical factors. Service providers
can then be confident that as more
subscribers or channels are added to the
network, channel zapping delays will not
be adversely impacted.
Testing IPTV Channel Zapping
IGMPv2/v3 supported over Well defined test cases cover the
Ethernet (with or without VLAN) most popular test scenarios
and ATM (1483 Bridged/Routed, The N2X IPTV channel zapping solution
SNAP, VC-mux) provides the most popular test cases that
As access networks migrate from ATM to enable test engineers setup the tests
Ethernet, it is critical to be able to test your quickly and get ready-to-go test results
multicast network implementation using along with easy-to-read diagrams after the
both technologies. The IPTV Channel tests. The test cases include IGMP Join
Zapping software provides support Delay, IGMP Leave Delay, Channel
subscribers on both ATM (OC-3c/12c) and Zapping, Resilience to Peak Load,
Ethernet (10/100 and Gigabit) interfaces. Sustained Performance, etc.
VLANs can also be used to separate
subscriber traffic on the Ethernet access
interfaces. Multicast traffic can be
sourced on any N2X interfaces, including For further information about the N2X
Ethernet, POS and ATM, at rates up to IPTV channel zapping solution and other
40Gb/s. Additionally, IGMP versions 2 and test solutions on Multiplay testing,
3 are both supported. please visit:
IGMP Snooping and IGMP Proxy contact your Agilent Technologies
Reporting support representative.
IGMP snooping or proxy reporting are
used in today's access network devices
such as DSLAMs, OLTs, and EARs to
optimize the multicast bandwidth used in
the network. The N2X IPTV Channel
Zapping solution can be used to test and
characterized devices that implement
either proxy or snooping functionality.