Broadcast video over IP presents unique challenges

With 2006 coming to a close and the prospects for continued, accelerated growth of IPTV services next year, it seems appropriate to revisit the topics of Quality of Service (QoS) and Quality of Experience (QoE).

Cable, satellite and broadcast have set an expectation level among viewers for picture quality, channel changing and program selection. For IPTV providers to compete, they must offer at least the same level of viewer experience.

IPTV Update turned to Ian Valentine, director of marketing, video products at Tektronix, to gain some insight on how they can achieve that. Valentine is responsible for the development of the baseband and compressed video test product strategic roadmaps. His responsibilities include Tektronix’s IPTV strategic direction and the development of related video products.

IPTV Update: What is the impetus for IPTV services today given that telcos have been experimenting with delivery of video over their networks since the mid ‘90s?

Ian Valentine: The telcos find themselves in an increasingly complex market, putting them under extreme pressure to find ways to leverage their technology infrastructures in support of new business growth areas. Coupled with the increasing need for change, the technology requirements to support new, high-bandwidth services in the networks have become a reality.

IPTVU: For telcos to compete, they must deliver a television viewing experience at least as good as that offered by terrestrial broadcast, cable or satellite. What are the primary challenges telcos face in doing so?

IV: The reliable delivery of broadcast video over an IP network presents a number of unique challenges to service providers. Video requires guaranteed available bandwidth and is intolerant to network jitter and lost or out-of-sequence packets. Each of these affects the user experience, including picture quality and response times to remote-control commands.

The QoE is critical to the success of IPTV. Consumers will expect an experience equal to or better than their current TV experience. Anything less will be unacceptable because it could lead to rejection of the services and increase customer churn, which telcos are trying to avoid. QoE is heavily dependent upon the network QoS.

IPTVU: What are the primary factors that determine delivering acceptable QoS for delivery of video via an IP network?

IV: The first is having a high availability of and sufficiently guaranteed bandwidth to allow the successful delivery of the service. By nature, IP networks are “best efforts” networks and so the provision of guaranteed bandwidth is a major challenge. Without this, video delivery will be “bursty,” which will cause issues at the set-top box (STB). The STB expects its data at a constant bit rate and in the correct sequence.

Next is short transmission delay. In standard broadcast services, all channels are provided to the receiver, and upon selection of the desired channel, the receiver immediately retunes to the correct channel. In IPTV systems, the retuning occurs within the network with only the chosen channel being provided to the receiver. Transmission delay through the network impacts quality of experience for the user, and it affects the response time to requests from the remote control.

Third is low network jitter. Jitter affects the variability of packet arrival through the network. This can affect the way packets are handled at various network elements. If the jitter is too high, packet loss will increase as queuing software tries to load balance traffic at network elements. This variability can lead to buffer underflows and overflows at the receiving STB.

Finally, low packet loss is essential. For every lost IP packet, there are approximately seven video Transport Stream (TS) packets lost. Lost packets have the greatest impact on the quality of received video and will generally lead to highly visible blocking errors, stuck picture and poor audio. All these obviously reduce customer satisfaction.

IPTVU: What problems do telcos face during this initial phase of IPTV service roll-out?

IV: Those responsible for the system face a three-part problem. First, can the “IP pathway” be reliably set up and torn down? A triple-play network needs to assure availability of network resources and bandwidth to deliver video services. However, video is bandwidth intensive, so it is equally important to ensure that pathways that are no longer needed can be torn down successfully. This requires test equipment capable of establishing and testing the IP pathway and providing statistics on network jitter and packet loss. These needs also apply to the provision of VoIP services. Tektronix offers the Spectra2|VQM for testing the IP pathway.

Second, is the video right at the source and destination? Once the IP pathway is established, it is then essential that the video data that is pushed into and received from the pathway is correct.

This requires the monitoring and analysis of the transport streams at the output of encoders, multiplexers and the headend. At the receiver end, similar monitoring and analysis is required to ensure there has been no degradation of the video as it passes through the system. These are commonly referred to as User Plane measurements. Tektronix offers the MTM400 and MTS400 products for this task.

Finally, is it a great customer experience? The final stage of the early deployment phase is to configure the system to deliver a high QoE. This requires the optimization of Control Plane (IGMP and RTSP) parameters. It is these protocols that influence the response time to user requests made from their remote controls, which is commonly referred to as “zap times.” Zap times are heavily dependent on the time required for IGMP protocols to leave one service and join another. As larger systems are deployed, this will be a major issue as the network elements will need to deal with numerous commands from the individual households connected to the service. Tools to measure zap times and other protocol exchanges are required. The Tektronix Spectra2|VQM is suited to this application.

IPTVU: You’ve mentioned some of the test and measurement solutions Tektronix is offering for the IPTV environment. The company has a history of playing in both the television and telecommunications world. How does that affect your offerings?

IV: Tektronix video and telecommunications network management and diagnostics domain knowledge is both broad and deep, making the company uniquely positioned to testthe convergence of voice, video and data. Tektronix has the video and communications expertise to deliver the right test methodologies and solutions to help bring IPTV services to market.

Tektronix offers the broadest — across multiple standards and video layers — and deepest — in-depth generation and analysis — solutions for compressed video test. Tektronix’s video test portfolio offers products to address IPTV applications, including the MTM400, which is used for 24/7 monitoring of broadcast services; the MTS400, which is used for in-depth R&D prototype and conformance testing by STB and infrastructure vendors; and the Spectra2|VQM, which is used for Control Plane measurements and Go/No Go video measurements of active networks.

Tektronix is focused on developing the most advanced test and measurement equipment for emerging technology and will continue to drive innovative new products for the new digital and converged world to meet the needs of customers in both broadcast video and communications.

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