The development of Internet Protocol Television(IPTV) services is quickly becoming a central strategy formajor telecom operators, with Asia and Europe leading the industry interms of network deployments and customer adoption.
Unlike ordinary Internet video services that stream or downloadhighly compressed video to a PC screen, IPTV systems deliverhighquality standard-definition and high-definition (HD) videocontent in real-time to more demanding displays, such as large-screenTVs. This requires a stable and reliable high-bandwidth networkinfrastructure.
IPTV system deployments usually drive major upgrades to the networkinfrastructure to meet these requirements. They also demand new testand monitoring technologies to test and maintain that infrastructure.
Several telecom operators have delayed or scaled down their IPTVsystems until they are able to pinpoint the cause of system problemsthat degrade the quality of the IPTV service delivered to theircustomers. Improved IPTV test and measurement technologies are thennecessary to accelerate the commercial deployment and growth of IPTVservices.
Tuning in to IPTV
IPTV was conceived in the mid- 1990s by Gerry Pond, then CEO of NBTel,as a platform that would enable the company and its industry peers topenetrate the entertainment services business and leapfrog the existingservices delivered via satellite, coaxial cable and terrestrialbroadcast.
The use of IP was hotly debated by designers due to the inherentchallenge of delivering high-quality video at constant bit rates on atechnology best suited to support data communications.
This debate still continues to some degree today, but the compellingfact then and now is that IP provides engineers and service providerswith unmatched flexibility to develop and launch new products andfeatures that many consider are essential to win and keep customers inan increasingly competitive entertainment market.
After a three-year R&D program involving several technologypartners, NBTel launched the first IPTV system into commercial servicein 1999. The service, branded Vibe Vision, has attracted customers awayfrom cable TV – partly due to customer interest in its IP-enabledfeatures, such as TV-based Web access, e-mail, content navigation anddigital picture quality.
Within a few months, the service was adopted by 5 percent ofhouseholds in the serviced market, making it one of the fastest growingservices released by a telecom operator.
As more customers switched to the IPTV service, the importance ofcore video quality and reliability rose steadily. However, numerousfailure modes were not detected by existing network monitoring tools.Likewise, the available helpdesk tools fell short in dealing with keycustomer impacting network problems.
Over the past three years, a growing number of telecom operatorshave announced plans to introduce and market IPTV services to increaseand defend core telephony revenues.
But despite high-profile trials and significant investments innetwork infrastructure, less than 5 million households worldwide useIPTV services today. Many network operators have had to delay servicelaunches or constrain the marketing of the service due to ongoingchallenges with service quality and reliability.
|Figure1: A simple IPTV end-to-end system has signal acquisition, videoencoding and compression, middleware, transport, access and homenetwork including one or more STBs.|
To better understand the IPTV service quality problem, let's review asimplified model of an IPTV network. Figure1 above shows a typical end-to-end system encompassing signalacquisition, video encoding and compression, middleware, transport,access, and a home network, including one or more STBs.
IPTV services impose critical demands on video encoders, transportnetworks, home network devices and higher-layer applications,especially middleware and video-on-demand (VoD)applications. The challenges associated with each of these subsystemsare discussed in detail as follows:
Signal acquisition and head-end. Since most of the video contentavailable today is intended for distribution over satellite or cable TVnetworks, it is typically delivered to the telco head-end as a variablebit rate service with bandwidth spikes exceeding the available capacityon the IPTV network.
The telco head-end must convert this variable bit rate content intoa compressed constant bit rate service. Generally, the bandwidthreserved for each channel of standard-definition content is in therange of 3Mbps, while HD content requires five to six times thisbandwidth. Newer compression systems can reduce this bandwidthrequirement by up to 50 percent.
This degree of compression and processing requires careful tuning ofup to 20 discrete parameters on each encoder and there are oftenseveral hundred channels available in IPTV systems. Once an optimalencoder profile is established, it must be maintained to account forongoing changes in the video path upstream of the telco head-end.
IP transport and distribution networks. On exiting the head-end, thevideo payload, comprising 50- 250 channels of linear broadcast traffic,is transported to regional distribution centers and then to localcentral offices. The broadcast payload, excluding overheads, ranges upto 750Mbps. Including overheads and VoD content, the aggregatedistributed bandwidth requirement can easily exceed 1Gbps.
Network jitter is currently the subject of considerable interest asa source of video impairment. However, since equipment vendors adapttheir products to support video traffic, jitter performance hassteadily improved. Likewise, STBs have become more resilient to networkjitter due to continued expansion of video buffers.
A key challenge in the IP infrastructure is ensuring adequatecapacity and performance as the network evolves to expand serviceareas, introduce new features and add customers. This requires strictcontrol of changes to the network, particularly as new technologies ornew versions of existing technologies are introduced into production.
Access and home networks. The last mile, home network and STBconstitute the largest component counts in the IPTV system. In thesenetwork segments, there is minimal application of automated failoverdevices.
The last mile and home networks are subject to a greater range ofenvironmental impacts. Moreover, the service may be negatively impactedby consumer actions and by field technicians who are not even awarethat they are affecting the IPTV service as they perform maintenance onthe telephony network, which also serves IPTV.
STBs and their on-board software are key components in the deliveryof the IPTV service. In addition to their video decode functions, STBsusually maintain program guide data, manage middleware transactions andsignal channel changes, and support the user interface.
|Table1: The subsystems in the network have specific video test andmeasurement requirements.|
Table 1 above summarizes thetest and measurement requirements associated with each of the majorsubsystems in the IPTV network.
Broadband IP network technologies and products are rapidly evolvingto meet the unique challenges of IPTV. Combined with rigorous networkchange control procedures, current developments in passive IPTV testand monitoring technologies and emerging end-to-end video monitoringsystems are expected to accelerate the deployment and improvescalability of IPTV systems while maintaining essential video qualityand reliability.