Broadcast video over IP presents unique challenges
Dec 27, 2006 8:00 AM
Ian Valentine, Tektronix director of marketing, video products, says video requires guaranteed available bandwidth and is intolerant to network jitter.
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.
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