SIMPLIFYING IPTV FIELD TESTING

Chris Dunford, Product Manager — Access Business Unit

Telecom service providers are presently in the race to deploy quality triple-play services, yet the most significant and oftenunderestimated service is Internet protocol TV (IPTV). IPTV quality of service and quality of experience are mandatory, since these arethe first service offerings that subscribers use to compare against existing services offered by cable television (CATV) and satellitecompanies.

Virtually any impairment on the network can affect the customer experience and the quality of the IPTV stream. When user datagramprotocol (UDP) is used, there is no retransmission of the lost packets and, as a result, the quality of the IPTV is affected to variousdegrees since the packet loss contributes to gaps in the IPTV stream. Therefore, the signal quality across the IPTV network must bemonitored to minimize customer complaints of poor service. Consequently, effective and thorough testing is an absolute necessity toaccomplish a successful IPTV service deployment.

Dealing with IPTV Issues

There are a number of issues that impede the quality of IPTV deployments, such as whether the customer is experiencing pixelization,tiling or freezing, which can be attributed to packet loss, packet jitter and/or delay. Technicians must be prepared to face thesesituations and be able to identify where the problems are coming from and whether the issues are related to the core network or in thedigital subscriber line (DSL)-fed access network.

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Figure 1. Typical IPTV deployment architecture.

Figure 2. Example of pixelization vs. clear picture.

Loss of IP packets (ultimately those carrying MPEG information) may occur for multiple reasons—bandwidth limitations, networkcongestion, failed links and transmission errors. Depending on the type of transport protocol used for the video streaming, a packet losswill affect the quality of the perceived video differently. When UDP is used, the lost packets will directly affect the image since theinformation cannot be recovered and the image will be corrupt or unavailable, and when transmission control protocol (TCP) is used, a packet loss will generate a retransmission, which can produce a buffer underflow that may result in a frozen image.

Loss of Ethernet packets, asynchronous transfer mode (ATM) cells and DSL frames will also cause IP packet loss since transmissionover these technologies is expected in the telecom-service-provider environment. For example, the loss of ADSL2+ frames in the localloop due to an impulse-noise spike will disrupt all information encapsulated within.

Jitter is the variation in arrival time between packets. A constant rate of packet arrival is preferred; however, the IPTV system can accepta certain amount of jitter—too much jitter will result in lost packets. Jitter not only happens to the IP packets, but also to the MPEGpacket (from the perspective of the MPEG encoder/decoder’s program clock reference); this is referred to as PCR jitter, in which thesystem attempts to maintain the 27 MHz clock used in the encoding of the MPEG packet. In this case, the set-top box (STB) must usethe 27 MHz clock to reconstruct MPEG during decoding.

The key to successful IPTV deployments is to keep packet loss, jitter and delay to a minimum (or eliminating them altogether). EXFO has the solutions required to help telecom service providers achieve these goals quickly and accurately.

Expertise in IPTV

EXFO’s AXS-625 30 MHz Copper and ADSL2+ Tripe-Play module for the AXS-200 SharpTesterprovides technicians with a reliable handheld test set for field installation, maintenance andtroubleshooting of their IPTV, VoIP and Internet service deployments. The AXS-625 allows fieldtechnicians to fully test these services in Through mode directly inside the house or in Stand-Alonemode when access to the customer premises is not available. The AXS-625 provides ADSL2+and Ethernet interfaces for telecom service providers to accurately and fully assess broadbandresidential triple-play services.

Figure 3. Translation of MPEG packets over multiple open-system interconnection (OSI) layers

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The AXS-625 provides four modes of operation to simplify IPTV deployments:

ADSL2+ Testing in Through Mode

The AXS-625 performs the analysis of IPTV services by replacing the user’sbroadband modem/router. In Through-mode configuration, the user connects theSTB as the end-point device, and the STB will perform the regular registrationprocess with the middleware located at the central office (CO) or the video head-end.

ADSL2+ Testing in Termination Mode

If no access to the customer premises is available or the STB is unavailable orfaulty, the AXS-625 can also be used in Termination mode, in which case theunit is capable of emulating the STB by way of Internet group-managementprotocol (IGMP) to join/leave the requests.

Ethernet Testing in Through Mode

In Ethernet mode, the AXS-625 performs the analysis of IPTV service with theunit placed between the modem and the STB. In a Through mode configuration,the user will connect the STB as the end-point device.

Ethernet Testing in Termination Mode

Services can also be tested in Termination mode via the Ethernet WAN interface.The only difference is that the AXS-625 is connected to the modem/router.

No matter how the AXS-625 is used, the IPTV test results are provided in a simple and user-friendly way.

The Test Summary page indicates IPTV pass/fail results at a glance:

VOICE

ETH

ERN

ET

ADSL2+DATA

VIDEO

VOICE

ETH

ERN

ET

DATA

VIDEO

Figure 6. Test Summary screen.

Figure 4. Testing ADSL2+ services in Through mode.

Figure 5. Using AXS-625 in Ethernet Through mode.

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The per-layer histogram provides a key tool for determining where problems arelocated—whether in the core or in the local loop.

Packet jitter is shown by a sliding graphical window with maximum and averagejitter recorded for the analyzed IPTV stream.

Program clock reference (PCR) jitter is shown by a sliding graphical window withthe average jitter recorded for the analyzed IPTV stream: If one channel reportspoor PCR jitter, this indicates that a source is the problem, and if all channelsreport poor PCR jitter, it is network jitter

Figure 7. The ERR Indicator shows detailed errorstatus.

Figure 8. IP Arrival Jitter screen.

Figure 9. PCR Jitter screen.

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Media delivery index (MDI): Defined by RFC-4445—is a key IPTV meanopinion score (MOS) scheme that provides a tool to measure and diagnosenetwork-induced impairments for IPTV streaming media. MDI is comprised ofdelay factor (DF) and media loss rate (MLR)

Delay factor (DF): Time value indicating how many milliseconds of videomust be buffered in order to cancel network-induced jitter, thus preventingpacket loss.

Media loss rate (MLR): Count of lost or out-of-order flow packets overa selected time interval, usually 1 second.

The AXS-625 packet identifier (PID) viewer displays statistical information,including PID number, rate and packet errors for the video, audio, PCR, and other tables—program association table (PAT) and program map tables(PMT)—for each MPEG video program stream.

A common PID mapping problem at the head end is when you have videowithout sound.

The AXS-625 measures network Zap time and displays IGMP joins/leaves to ensure the network is responding quickly enough and when the channelsare correct.

Conclusion

The AXS-625’s approach of IPTV testing greatly facilitates the rollout of IPTV services, which makes the technician’s job easier. Once the technician connects the line to the unit, receiving the test results and ensuring quality IPTV deployment is just seconds away.

Figure 10. Stream Parameters screen showing MDI results.

Figure 11. Stream Content screen showing PID valueand the rate.

Figure 12. IGMP monitor screen.

Appnote175.1AN © 2008 EXFO Electro-Optical Engineering Inc. All rights reserved. Printed in Canada 08/04

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