Video traffic is the last big challenge for telecom carriers to master before they can bring IP-based triple play services to mass deployment.And there’s a reason for that.Compared to voice and data services, video traffic has the most complex requirements. For video, the consumer experience must be top notch, since users will be comparing IPTV to their traditional TV service. There will be no room for delays or interruptions in service, and channel changes must be lightning fast. The service must also be reasonably priced.

These needs translate to technical requirements for high bandwidth (especially as consumers move to high-definition TVs), high reliability, and a high degree of service awareness to make video delivery as efficient as possible. IP-based services offer carriers the opportunity to achieve dramatic savings by collapsing all three service types—voice, data, and video—onto one network infrastructure. IP service awareness is the key to making these systems efficient and cost-effective.

The many advantages of IP

Customers want more service bundles and choices. To satisfy this demand, carriers can either provide an overlay for each service, or combine all of the services into a single network with Quality of Service (QoS). Most carriers are choosing the latter approach, converging onto an IP network because the costs are lower.

But that puts a QoS burden on the network. Different service types require different levels of QoS, so the converged IP network must be service aware: it must be able to detect the service type (voice, video or data) and apply the appropriate QoS level.

In an IP network, the network can treat services as applications instead of as circuits. For this to work, the IP network must be able to distinguish each service being delivered, so carriers can provide high service quality for their customers while maintaining high network efficiency and low costs. IP service awareness allows carriers to save money with a converged network while offering QoS appropriate to each service type.

IP service awareness marks a fundamental shift in the way telecommunications services are provided. The existing B-PON and DSL access equipment is built on ATM, which dictates a bottom-up approach to QoS. Typically, the carrier provisions a circuit and assigns it to a QoS class. As new applications are developed, they are either assigned to one of the existing ATM circuits, or a new circuit is created with a different QoS commitment. This type of system is inherently circuit-aware and assigns QoS to circuits (unless it terminates ATM directly).

The service aware access network

But advances in access equipment are changing the way services are provisioned. Newer GPON and VDSL2 technologies (which are native Ethernet protocols), are replacing ATM-based access networks. These GPON- and VDSL2-based access systems switch traffic at Layer 2, but they also provide service awareness at higher network layers, thereby shifting the role of policy enforcement out of the Broadband Remote Access Server (BRAS) and into the access equipment itself. So instead of the bottom-up approach to QoS, GPON and VDSL2 enable a top-down approach: the service-aware IP network automatically determines the QoS required for each application and translates it into policies.

Multicasting for peak efficiency

In order to gain the maximum benefit from IP efficiency when delivering video, IPTV providers must implement multicasting. Multicasting dramatically reduces bandwidth requirements by enabling carriers to transport one copy of video content deeper into the network and then replicate it as close to the consumers’ homes as possible. This requires a high degree of service awareness from the access equipment because the consumer may be receiving on-demand video (a unicast service) as well as broadcast video (a multicast service).

Traditionally, the BRAS has shaped flows into the access network, controlling QoS from afar. However, IPTV services are deployed today by multicasting to subscribers from the local access node or even closer, from a PON-fed ONT in the subscriber’s dwelling. The BRAS does not have real-time knowledge of IP multicast bandwidth usage because channel changes are handled directly from the access node. At the same time, unicast VOD is still driven from the BRAS.

IPTV requires that the access node balance multicast and unicast traffic. The access network must be aware of the VOD streams that flow through it and adjust the multicast bandwidth accordingly.

In addition to increasing flexibility and lowering network complexity, IP service awareness also enables the revolutionary impact of IP Multimedia Subsystems (IMS). IMS is a standards-based core network framework that unifies the various service technologies for both wireline and wireless networks. It promises to enable dynamic service delivery over any access network. And that means even more tailored services for the consumer, and an unprecedented amount of mobility. For example, phone service can follow people as they move from their cars into their houses or vice versa. The IMS (specifically, the Remote Access Control Facility) decides how to allocate bandwidth between multicast and unicast, and then the access node enforces the constraint.

The best is yet to come

IPTV is only the beginning. IP network service flexibility will also enable the creation of new services, especially in the gaming area. The network designed today must be flexible enough to accommodate new demands without requiring a major overhaul.

Point-to-point IPTV and interactive gaming are two services that are emerging over the Internet. Like multicast service, point-to-point streaming video requires a constant bit rate—not just from the multicast point, but all the way back to the video source closer to the core of the network. It may also require a more robust signaling path to secure the service from a server in the network. Both IPTV multicast and IPTV point-to-point will require more bandwidth for an HDTV service—19 Mbps with MPEG2 and 8-9 Mbps with MPEG4 or other higher compression standards.

Video games generate bursty traffic and can often perform well with lower bandwidth. What gamers need, however, is low latency: shots or moves must happen very quickly to keep pace with the action or hit their targets. Like VoIP, both gaming and point-to-point video are becoming popular using Internet access technology, but the experience will be improved as the access network becomes aware of the specific requirements for each of these new services.

For example, a customer might order a video service over his Internet connection (which is best-effort QoS). When the IMS receives the service order, it commands the GPON network to provide IPTV multicast QoS, and the IPTV service is sent to the viewer using a constant bit-rate QoS. As the viewer finishes watching the video, he might be offered a chance to play a video game associated with the show. When the customer orders the video game, the IMS dynamically orders a new QoS for the gaming flow. The gaming QoS would provide less bandwidth but also lower latency. The bandwidth that was previously used for the IPTV service would be released for reuse by another service. Then, as the game proceeds, the viewer might be offered a chance to participate in a chat service with a voice component. At this point, the IMS would adjust the QoS again, this time for even less bandwidth, but with a guaranteed rate and low delay to optimize the voice experience.

Matching bandwidth, latency, and other attributes with individual services allows the carrier to optimize bandwidth across the network for the specific services in use at any given time. With a growing array of IP services in our future, carriers can’t afford not to optimize bandwidth. IP service awareness provides the missing link in service delivery. It creates a flexible, efficient network that can handle varying QoS requirements for the services consumers want today along with the new applications yet to come, all at a reasonable price and without compromises on service quality.

Don McCullough is director of product marketing for Entrisphere.