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Delivering the next big motion picture: IPTV

Posted: 05 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:internet protocol television? iptv?

By Seong-Hwan Kim and Deepak Kataria

Agere Systems

Network Systems Designline

Internet Protocol Television (IPTV) hype and activity has blasted onto the semiconductor and networking scene during the past year. While real-world use remains minimal and in its early stages, the technology's momentum is undeniable.

A key question affecting how much momentum this technology will gain and when it will happen is, "Will IPTV technology be as good as it can be?" As yet, there is no definitive answer. There are ways to make IPTV service better, and by doing so usage of the technology will likely grow. This article addresses these IPTV technological improvements aimed at enabling smarter IPTV services.

To put this subject in context, some basic background is instructive. Internet growth is forcing the technology to migrate from simple data services to triple play services. Triple play services include voice, data and video over a single transport infrastructure. This migration requires changes in physical medium that bring service to homes from current cable or satellite TV, to fiber to the premises (FTTP) or xDSL. Among triple play services, video service is particularly challenging because end users want to be able to see their TV program while surfing the web or making a phone call.

To achieve this end, key IPTV features needed include:

Selection: End users should be able to select their program of choice from a plethora of TV content available. This also requires faster channel selection and channel changing time.

Storage: TV content should be stored in a local storage device, so it can be made available to customers whenever they want to watch it. Some vendors are planning to store new TV programs or movies into the set top box (STB). Such a box could store up to 100 hours of programming.

Low cost: Per-line/per-customer cost of xDSL service must be low.

Quality of service: The service should guarantee bandwidth for video streaming and QoS differentiation for supported classes of traffic.

Upgrades: A service provider should be able to upgrade codecs and user authentication software without disrupting service.

Miscellaneous: Service providers should be able to provide high quality resolution for programs at no additional charge to end users.

Future IPTV service will provide two different types of TV services: standard definition (SD) and high definition TV (HDTV). SDTV bandwidth ranges from 1Mbps to 4 Mbps. HDTV bandwidth ranges from 4Mbps to 13Mbps.

The typical number of TV channels available using the service provider hovers between 250 and 300 channels, adding 10 to 20 more channels for HDTV. If each home has approximately four TVs, two to three SDTVs and one to two HDTVs can be supported with roughly 20Mbps bandwidth. At this point, bandwidth management among different traffic classes to homes becomes a critical issue, meaning that voice, video and data services must be handled differently.

From a QoS control perspective, traffic management in the IPTV network can be particularly challenging. This is because traffic management solutions have to be implemented at different levels of control granularity. Those levels include:

? the individual services active used by a given subscriber,

? the individual DSL link-load for the given subscriber,

? the aggregate subscribers supported on a given line card, and

? the aggregate line cards supported on a given uplink card.

To provide different levels of service, hierarchical traffic management as shown in Figure 1 would be ideal.

Figure 1: Downstream traffic management in network processor

There are two different aspects of layered traffic control. One is downstream (from service provider to end user, and the other is upstream (from enduser to service provider). In the downstream direction, hierarchical traffic management can provide differentiated services for different subscribers, because each user gets different service allotted by different schedulers.

In addition, class-dependent traffic isolation can be provided to the end user between different traffic streams. Per-user scheduler configuration can be mirrored to other users who request the same bandwidth and set of services.

In the upstream direction, individual user traffic gets monitored at the lowest level of hierarchical scheduler. And each class of traffic from different users can merge into a separate class scheduler (e.g. voice, data, and video) at the next level of hierarchical scheduler.

Having a separate class of scheduler will provide class isolation. Another benefit is that bandwidth starvation caused by lower/other class congestion will not occur. Having per-user scheduling can also provide end user isolation for billing and bandwidth control purposes.

Contemporary TV technology sends all TV channels to all end users and channels are changed by simple filtering of the undesired frequencies. This mechanism is used in existing digital TVs. Specifically, channel changing selects only one channel and ignores the rest. IPTV can not use this approach because of the bandwidth limits to each home. Therefore, the telecom service provider only sends the selected TV channel or channels to the customer premises.

This creates channel changing delay, because channel change information has to travel through the network to the service provider. But, if all content/channels reside as close to the end user as possible, use of a high capacity backplane enables dramatic reductions in channel changing delay. Specifically, this means bringing all content to the DSLAM box (which is located closer to end users) and snooping channel changing information there, instead of letting content travel all the way up to a broadband remote access server (BRAS).

One question many people ask is, "If all the TVs in a house are switched off, can end-users use more bandwidth?" Because end users are allowed to use their maximum bandwidth amount, 20Mbps for example, when TVs are turned off, the end user should be able to use the rest of the bandwidth for carrying other services.

This bandwidth adjustment does not have to be guaranteed (for oversubscription). But, the service provider should guarantee the minimum bandwidth. To achieve this, a DSLAM should monitor the status of TVs at home. If one or more TVs are turned off, a service provider may allocate more bandwidth to the end user's data service with best effort scheduling technology. When TVs are turned on, the service provider should reduce the scheduler rate of other services. The DSLAM controller must have a powerful scheduler to dynamically control bandwidth in this fashion.

Another factor that would make hasten the deployment of IPTV is lowering its cost. Some DSL vendors have tried to decrease the cost to $1 per line. That means a reasonably priced network processor would be required to provide proper QoS management, as well as all the benefits of traffic management technology. Another factor improving IPTV economics would be exploiting the synergies between telecommunications providers and cable TV providers. If these two rivals were to combine their services for wider deployment of higher performance, they could both provide more economical IPTV to customers.

About the authors

Seong-Hwan Kim is a distinguished member of technical staff for Agere Systems. He can be reached at

Deepak Kataria is systems engineering manager for Agere Systems. He can be reached at

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