Meeting the challenge: delivering optimal video-on-demand services

Today’s service providers are currently in a heated race to deploy next-generation services over their existing IP-based networks, and in essence offer a bundle of  multiple, converged services to subscribers (writes Mark Chaplain, VP EMEA at Ixia). The key strategic weapon in their arsenal is video-based interactive services, including broadcast IPTV and IP-based video-on-demand (VoD). These services promise to generate critically important new revenue streams necessary to offset the inexorable decline in their voice businesses, and help them gain market share by enticing customers to switch from competing satellite and cable offerings.

The VoD opportunity
Video-on-demand (VoD) is poised to become one of the most important video services offered over a converged IP network. Basic IP-based VoD service offers consumers a highly interactive, customised ‘anytime’ video experience by enabling users to request live and pre-recorded video content from a network-based library of content (such as new DVD movie releases) and allows them to watch this content immediately or during a set interval of time (usually within 24 hours). Additionally, users are able to interact with the video at will by performing DVR-like functions, and it’s possible to pause/resume, fast-forward or rewind or jump between ‘chapters’ (depending on the content being delivered).

Looking forward, VoD is perhaps the most critical and most promising elements of the multiplay service bundle, and can lead to an array of new, revenue-producing services for providers such as the marketing and selling of DVDs and customised video content, as well as a host of new interactive marketing services and applications that take advantage of the tight integration of multiplay services.  For example, it will be possible to integrate VoIP and video telephony within the video services framework to allow users to access personal directories and make and receive calls using their remote controls, and provide the means for subscribers to respond to video-based special offers and product/service discount vouchers – all from the living room sofa.

Business and technical challenges
The road to a successful VoD deployment is rarely smooth and straightforward, however, as there are multiple technical and business challenges associated with delivering a successful VoD service. Content acquisition, for one, is a critically important business challenge in that providers must form relationships with the right video content partners and license high quality ‘in demand’ content that will allow them to build a wide and deep catalogue of content – and ultimately a loyal customer base.

Other major technical challenges involve ensuring the customer’s quality of experience with the service is as optimal as possible, and that the switch from cable or satellite service is completely transparent. Specifically, providers must make sure customer expectations are met in terms of switching from ‘zero delay’ standard TV to IPTV, and therefore they must deliver fast channel change times and effectively manage network bandwidth. Providers must also ensure that the quality of the video delivered to the customer premise is as good as or better than what is currently available in the marketplace.

The reality is that VoD video traffic can be highly unpredictable, and scalability and network congestion issues can create service impairments that can quickly undermine a provider’s deployment.

Key deployment issues and test considerations
For a service provider to deliver the optimal quality of experience that’s essential for a successful deployment, there are a number of key deployment issues and considerations that must be taken into account. Each of these issues has the potential to impact the amount of network bandwidth available on the network, or the ability of the network to scale appropriately in order to meet the demands of subscribers.

Supporting multiple HDTV in the home: a typical European household has three or more TVs. As the market transition to high definition display technology enters full swing, it will be only a matter of time before all standard definition sets are replaced by HDTV. These facts have a direct implication on network bandwidth considerations.

Consider a common household, with the kids watching an on-demand Cartoon Network special, dad watching the Discovery Channel, and mum watching soap operas via VoD that she’s missed during the week - all on different TVs in different rooms of the house. Since each TV is tuned into a different video ‘channel’, the provider must be assured that it provides the right amount of bandwidth in order to support the delivery of all the requested video streams.

Indeed, this takes on special significance when each person is viewing high definition content: With today’s current IPTV network architectures, 1080p high definition video quality translates into approximately 18-20 Mb of bandwidth consumed per each high definition channel received. Multiply this by three (or more), and that’s around 80-100 Mbps of bandwidth that is required to provide video service to a typical household.

Other issues include taking into account potential interactions between all the TVs in the household. Since each TV is viewing different content, not only does the provider need to be assured that is has the right amount of bandwidth available to provide sharp, clear video and fast channel change times, it needs to ensure that user interactions with their TVs don’t have a negative impact on the other TVs in use.

New Coding and Connection Mechanisms: as current network speeds are not yet sufficient, today’s multiplay networks need to be optimised in order to support these new video services. A new breed of more efficient media encoding and connection methods – such as MPEG 4 -- helps to reduce the need for bandwidth. Such encoding mechanisms need to be accurately tested in pre and post deployment.

Unicast vs. multicast services: The reality is that the load on a network will be many times that with VoD (unicast) than with broadcast IPTV (multicast) services, and service providers must take this into account. Consider that in large urban environments, it will be increasingly common for large groups of people in large residential buildings to purchase the same VoD content, and this will have a direct impact on the amount of bandwidth that is available.

In addition, service providers must correlate the interaction of VoD with multicast services as they work in the network, and not just test them individually. Obviously, both types of services need to coexist on the network, and testing the interoperation of both services in a realistic environment is essential for gaining a real-world assessment of performance.

Testing VoD interactive services: a compelling argument for the success of IP-based VoD is the power and ease of use of the service. Users can preview channels, make context sensitive searches within the catalogue of video content, etc. Therefore, it is important to test the performance of the network-based catalogue of videos that are available, and other interactive features.

Troubleshooting network prioritisation mechanisms: in an IP-based multiplay network, even if enough bandwidth is available to effectively support services, there is still a need to ensure that priorities are applied correctly to the type of traffic occurring on the network. Authentication, authorisation and packet inspection systems are used to perform this function, and if video payloads are encrypted there is risk that video could get treated as data and not video content. If a provider prioritises video content over data packets (which is usually the case since video traffic is highly delay sensitive and requires such special treatment), such cases of mistaken identity could result in the video getting blocked or corrupted in the delivery network since the special treatment required wouldn’t occur.

The impact of peer to peer (P2P) traffic: Today, P2P traffic is the single largest threat to service provider SLAs. Because VoD and IPTV services ride on an existing IP network that is used for both voice and Internet data traffic, there is the need to manage the load from P2P traffic.  In fact, a lot of P2P traffic – such as Skype and BitTorrent and myriad file sharing services – operates in a sort of stealth mode, using non-standard ports and non-standard services. This traffic adds additional load on the network, and to make matters worse, any detection equipment in use to identify P2P traffic may also add delay into the network, adversely impacting video.

The impact of other concurrent services: Likewise, there are a host of other applications and services that may be running concurrently on the network, and each can takes its toll in terms of bandwidth consumed and load on the network. Such services include online gaming, telecommuting, interactive advertising and transaction services, VPN connections, and even Web-based streaming video from the likes of youtube.com.

Developing a holistic VoD testing methodology
In order to mitigate these challenges, service providers need to invest in specialised multiplay test equipment and develop holistic testing techniques that will allow them to assess the performance of their network designs with every new tweak. In short, they need to perform ongoing testing while they are fine tuning during both pre and post deployment phases.

The VoD components that require testing include content acquisition systems; content encoding systems; VoD media servers; network switching and routing platforms; packet inspection systems; and customer premise equipment, such as set top boxes.

Some of the key requirements for testing VoD infrastructure include:

1. Measuring the performance of an IPTV deployment
2. Determining the availability of the network to carry the video data
3. Measure the impact of network characteristics on video quality
4. Measuring the impact of middleware devices - encoders, digital media rights management systems, billing systems, add insertion devices, and conditional access systems - on network performance
5. Assessing the perceived quality of the video content
   

Testing must also determine the number of active video clients that a VoD server can handle, whereby the maximum client capacity of a server is the threshold - at which the server can no longer support any additional clients without degradation of quality in the video media streams.

The video server components must be able to support sudden increases in bandwidth and resource utilisation. With a sudden increase of bursty traffic (many on-demand requests from subscribers), the rate of arrival of requests for new content may overwhelm the VoD system. Therefore, tests must measure the ratio of successful video streams delivered over the total number of requests received. This is important for modelling the scalability of a given VoD system so that providers know how to invest in the appropriate infrastructure in order to keep up with the project growth of on-demand content.

In addition, the testing of the network performance of a video server must characterise latency experienced by clients, jitter introduced on the video streams and losses due to oversubscription of resources. Characterising how well the VoD servers deliver video is important because service providers need this information to ensure they can scale to match the projected user demand.

In addition to video servers, video cache devices which replicate frequently accessed content by several thousand users must go through a similar network performance characterisation.

Finally, throughout the individual component testing that is performed, the goal is to ensure that the video delivered into the service provider’s network is of the best possible quality. Therefore an overall requirement is to know the experience of users in watching the VoD content. This includes the effects of the network on the video stream, and also determining a user’s perceived quality of experience based on subjective video analysis.

Meeting the VoD QoE challenge
The challenge for today’s service providers is to ensure that their VoD service is comparable, if not superior to what their new subscribers have been accustomed to. On the business side, they must determine how they can offer the best content and have their customers pay the least for it.

They also need to make sure the offer is more compelling than the experience of playing a DVD, and to ensure that the experience they offer for the first time is compelling enough that they do not turn away the early adopters. Indeed, once a customer turns away, it will be an extremely tough – if not impossible - sell.

In order to ensure a successful VoD deployment, it is critical that telcos understand that the VoD service is not a separate function from their existing IP network infrastructure. In order to validate the quality of the service offer, pre- and post deployment testing is an essential undertaking that involves not only testing specific, individual network components but also testing VoD service from a systematic, holistic point of view.

Ultimately, service providers need to test their VoD deployments according to what happens in the field during real-world scenarios, where they are able to correlate tests of the various services and applications running on their multiplay networks as they relate to real-world network dynamics. It is simply not enough for a provider to perform video tests based on the load created by a million users – it is essential that they test these users while other subscribers are making voice calls and downloading music files – in essence during real-world traffic conditions.

Finally, service providers need to ensure that an adequate degree of scalability exists in their test network in order to ensure that their new multiiplay network can scale for the foreseeable future.