APPLICATION NOTE Telecom Test and Measurement SIMPLIFYING IPTV FIELD TESTING. Dealing with IPTV Issues

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1 APPLICATION NOTE 175 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 often underestimated service is Internet protocol TV (IPTV). IPTV quality of service and quality of experience are mandatory, since these are the first service offerings that subscribers use to compare against existing services offered by cable television (CATV) and satellite companies. Virtually any impairment on the network can affect the customer experience and the quality of the IPTV stream. When user datagram protocol (UDP) is used, there is no retransmission of the lost packets and, as a result, the quality of the IPTV is affected to various degrees since the packet loss contributes to gaps in the IPTV stream. Therefore, the signal quality across the IPTV network must be monitored to minimize customer complaints of poor service. Consequently, effective and thorough testing is an absolute necessity to accomplish a successful IPTV service deployment. Figure 1. Typical IPTV deployment architecture. 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 these situations and be able to identify where the problems are coming from and whether the issues are related to the core network or in the digital subscriber line (DSL)-fed access network. Figure 2. Example of pixelization vs. clear picture.

2 Loss of IP packets (ultimately those carrying MPEG information) may occur for multiple reasons bandwidth limitations, network congestion, failed links and transmission errors. Depending on the type of transport protocol used for the video streaming, a packet loss will affect the quality of the perceived video differently. When UDP is used, the lost packets will directly affect the image since the information 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 transmission over these technologies is expected in the telecom-service-provider environment. For example, the loss of ADSL2+ frames in the local loop due to an impulse-noise spike will disrupt all information encapsulated within. Figure 3. Translation of MPEG packets over multiple open-system interconnection (OSI) layers Jitter is the variation in arrival time between packets. A constant rate of packet arrival is preferred; however, the IPTV system can accept a certain amount of jitter too much jitter will result in lost packets. Jitter not only happens to the IP packets, but also to the MPEG packet (from the perspective of the MPEG encoder/decoder s program clock reference); this is referred to as PCR jitter, in which the system attempts to maintain the 27 MHz clock used in the encoding of the MPEG packet. In this case, the set-top box (STB) must use the 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 MHz Copper and ADSL2+ Tripe-Play module for the AXS-200 SharpTester provides technicians with a reliable handheld test set for field installation, maintenance and troubleshooting of their IPTV, VoIP and Internet service deployments. The AXS-625 allows field technicians to fully test these services in Through mode directly inside the house or in Stand-Alone mode 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 broadband residential triple-play services.

3 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 s broadband modem/router. In Through-mode configuration, the user connects the STB as the end-point device, and the STB will perform the regular registration process with the middleware located at the central office (CO) or the video headend. VOICE DATA ETHERNET ADSL2+ ADSL2+ Testing in Termination Mode VIDEO If no access to the customer premises is available or the STB is unavailable or faulty, the AXS-625 can also be used in Termination mode, in which case the unit is capable of emulating the STB by way of Internet group-management protocol (IGMP) to join/leave the requests. Figure 4. Testing ADSL2+ services in Through mode. Ethernet Testing in Through Mode In Ethernet mode, the AXS-625 performs the analysis of IPTV service with the unit 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. VOICE DATA VIDEO ETHERNET Figure 5. Using AXS-625 in Ethernet Through mode. 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: Figure 6. Test Summary screen.

4 The per-layer histogram provides a key tool for determining where problems are located whether in the core or in the local loop. Figure 7. The ERR Indicator shows detailed error status. Packet jitter is shown by a sliding graphical window with maximum and average jitter recorded for the analyzed IPTV stream. Figure 8. IP Arrival Jitter screen. Program clock reference (PCR) jitter is shown by a sliding graphical window with the average jitter recorded for the analyzed IPTV stream: If one channel reports poor PCR jitter, this indicates that a source is the problem, and if all channels report poor PCR jitter, it is network jitter Figure 9. PCR Jitter screen.

5 Media delivery index (MDI): Defined by RFC-4445 is a key IPTV mean opinion score (MOS) scheme that provides a tool to measure and diagnose network-induced impairments for IPTV streaming media. MDI is comprised of delay factor (DF) and media loss rate (MLR) Delay factor (DF): Time value indicating how many milliseconds of video must be buffered in order to cancel network-induced jitter, thus preventing packet loss. Media loss rate (MLR): Count of lost or out-of-order flow packets over a selected time interval, usually 1 second. Figure 10. Stream Parameters screen showing MDI results. 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 video without sound. Figure 11. Stream Content screen showing PID value and the rate. The AXS-625 measures network Zap time and displays IGMP joins/leaves to ensure the network is responding quickly enough and when the channels are correct. Figure 12. IGMP monitor screen. 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.

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