Simplifying IPTV field testing


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Simplifying IPTV field testing

  1. 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. Telecom Test and Measurement
  2. 2. APPLICATION NOTE 175 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-625 30 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. Telecom Test and Measurement
  3. 3. APPLICATION NOTE 175 The AXS-625 provides four modes of operation to simplify IPTV deployments: ADSL2+ Testing in Through Mode VOICE The AXS-625 performs the analysis of IPTV services by replacing the user’s ETHERNET 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 DATA ADSL2+ process with the middleware located at the central office (CO) or the video head- end. VIDEO ADSL2+ Testing in Termination Mode 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 Figure 4. Testing ADSL2+ services in Through mode. protocol (IGMP) to join/leave the requests. 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, VOICE ETHERNET the user will connect the STB as the end-point device. Ethernet Testing in Termination Mode DATA 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. VIDEO 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. Telecom Test and Measurement
  4. 4. APPLICATION NOTE 175 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. Telecom Test and Measurement
  5. 5. APPLICATION NOTE 175 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. Telecom Test and Measurement
  6. 6. EXFO Corporate Headquarters > 400 Godin Avenue, Quebec City (Quebec) G1M 2K2 CANADA Tel.: 1 418 683-0211 Fax: 1 418 683-2170 Toll-free: 1 800 663-3936 (USA and Canada) EXFO America 3701 Plano Parkway, Suite 160 Plano, TX 75075 USA Tel.: 1 800 663-3936 Fax: 1 972 836-0164 EXFO Europe Omega Enterprise Park, Electron Way Chandlers Ford, Hampshire S053 4SE ENGLAND Tel.: +44 2380 246810 Fax: +44 2380 246801 EXFO Asia 151 Chin Swee Road, #03-29 Manhattan House SINGAPORE 169876 Tel.: +65 6333 8241 Fax: +65 6333 8242 EXFO China No. 88 Fuhua, First Road, Central Tower, Room 801 Shenzhen 518048 P. R. CHINA Tel.: +86 (755) 8203 2300 Fax: +86 (755) 8203 2306 Futian District Beijing New Century Hotel Office Tower, Room 1754-1755 Beijing 100044 P. R. CHINA Tel.: +86 (10) 6849 2738 Fax: +86 (10) 6849 2662 No. 6 Southern Capital Gym Road Appnote175.1AN © 2008 EXFO Electro-Optical Engineering Inc. All rights reserved. Printed in Canada 08/04