Quality of service for IPTV
01 January 2009 |
One of the biggest problems for telecoms operators involved in IPTV is that of broadband capacity constraints in their access and aggregation networks. With over-the-top services such as Youtube, bandwidth consumption is growing faster than new capacity can be deployed.
Simply, when there is not enough bandwidth, IP packets can be delayed, lost or arrive out of order. For IPTV the consequences of insufficient network resources can be pronounced: heavy pixelation, frozen and blank screens, degradation of audio, slow or frozen channel change and loss of interactivity. This doesn’t just affect the “extra” users who are causing the network resources to be over subscribed, but will impact the quality of experience (QoE) for all consumers.
IPTV – a difficult business case
The challenge for the success of IPTV is not just technical – the business case for IPTV is a difficult one. First-year installation and support costs run into hundreds of dollars per household. To make a return on these huge investments, service providers need to offer more than an imitation of what is already available from incumbent broadcast, cable and satellite providers. IPTV offers the opportunity for extreme personalisation and interactivity of content and advertising – far beyond that offered by the traditional television service. For the operator achieving these features and guaranteeing a high quality of service involves complex infrastructure. While basic IPTV services are generally multicast to the user base in order to achieve network resource efficiency, the bandwidth becomes very scarce when users can also access time-shifted and libraries of on-demand content using individual unicast streams. Service providers looking to make the business case for IPTV will need to offer personalised, contextual and interactive advertising. The problem is that these require an individual stream to each consumer.
The demands on the network will be highly volatile depending upon viewing habits, the amount of personalised content, the interactivity of services, and how much targeted advertising is offered. These are only a few of the capabilities we will see when fully mature “second generation” IPTV services are deployed. And we have not even mentioned the impact of multiple set-top boxes per household, demand for high definition, blended IP services and so on.
Vying for space on the network
IPTV services will have to contend for space on the network with many other services like peer-to-peer, gaming and a plethora of over-the-top services. Further complications arise because of the dynamic nature of the network environment. For many years to come, the principal access network technology will be a flavour of DSL – and as is well-known the line rate can vary depending upon distance from the exchange, noise, changes to routing tables, and so on.
This makes IPTV harder to manage and engineer than any other IP service precisely because of the idiosyncrasies of user activity and the variability of the network environment. Traditionally operators have had some control over quality of service through application-specific policy control solutions, these approaches are limited in that they can only be aware of the individual application that they are managing.
Alternatively putting IPTV into a stove-pipe of dedicated network resources effectively “sterilises bandwidth” as it is unavailable for other applications – this undermines the basic rationale for a common all-IP network. Furthermore, this is a costly and inefficient process which delays the launch of new services – and also means incremental network capacity cannot be exploited without re-engineering the applications.
What’s the alternative?
Fortunately, a better alternative exists. In recent years the industry has put much effort into developing standards for Resource and Admission Control, for example ETSI TISPAN’s RACS (Resource and Admission Control Subsystem). These are ideally suited to solving the technical and commercial challenges of IPTV.
When applied to an IPTV solution, the RACS is located between the IPTV middleware and the transport network, a position from which it is able to become a single point of contact to which applications can request bandwidth. The middleware is able to make session requests and the RACS is then able to enforce subscriber and service policies, allocating network resources on real-time, per session basis, removing any need for the IPTV application to understand the underlying and frequently complex topology of the network.
This means RACS is able to view the network as an all-IP resource, available to all applications thus allowing operators to be more flexible in their service offerings. Operax for example, has extended the principle laid out in the standards to offer dynamic Resource and Admission Control. This tracks the available bandwidth and resources in the access, aggregation and core networks, so that each IPTV session is only started if there are truly resources available to carry it.
With this approach service providers can offer an extensive range of personalised interactive content and advertising. This will mean that not only are consumers more willing to pay for premium services with a great quality of experience, but also that advertisers can be assured of an extremely effective and valuable medium for their messages.
Chief marketing officer, Operax
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