IPTV services are part of a broader carrier trend under which carriers plan to converge their networks on a single, IP-based backbone. In an all-IP network, the network can treat services as applications instead of as "nailed-up" circuits, thereby eliminating the need for overlay networks and consequently reducing provisioning and management costs.
Existing BPON and DSL access equipment is built on ATM, which dictates a circuit-based approach to services: each new service is either assigned to one of the existing ATM circuits, or the carrier creates a new circuit with a different QoS commitment. 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 (B-RAS) and into the access equipment itself. So rather than providing a specific circuit for video services, GPON and VDSL2 allow the service-aware IP network to automatically determine the QoS required for each application and then translate those requirements into specific policies.
But with all services converged on an all-IP network, the network must be able to differentiate between services and apply the appropriate QoS, and this is particularly important for IPTV. Video traffic is a particularly challenging service to deliver on a converged network. Carriers must offer a highly reliable, high-quality viewing experience that compares favorably against traditional TV service. In addition, video services, especially HDTV, require that the carrier deliver more bandwidth. Figure 1 shows that bandwidth demand must scale up to 50 Mbps. The service must be competitively priced, and consumers must experience no delays in channel changing or any other interruptions in service.
These needs translate to technical requirements for high bandwidth (especially as consumers move to HDTVs), 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 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 issue then becomes controlling the various bandwidth demands of these services: data, video on demand (VoD), and IP multicasting.
Traditionally, the B-RAS 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, such as from a PON-fed ONT in the subscriber's dwelling. The B-RAS 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 B-RAS. As shown in Figure 2, the B-RAS can only control the bandwidth demand in a static manner.
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.
IPTV is only the beginning. IP network service flexibility will also enable the creation of new services, especially in the gaming area. Today, point-to-point IPTV and interactive gaming are emerging over the Internet, and with all-IP networks, carriers can offer them both as well. 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 MPEG-2 and 8 to 9 Mbps with MPEG-4 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. As other services such as VoIP are combined with gaming and IPTV, QoS awareness and control becomes much more important.
For example, suppose a customer orders a video service. 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. When the viewer finishes watching the video, he may want to play a video game based on the show he just watched. At this point, 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 (VoIP). 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, and IP service awareness is the key. With a growing array of IP services in our future, carriers cannot afford not to optimize bandwidth. IP service awareness provides 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.
