Video Over IP
The basic telco TV systems architecture consists of digital headend equipment, the core network, the access network, and one or more IP set-top boxes per home.
The headend is typically centered around the video content processor, a piece of equipment capable of sourcing broadcast video from both analog sources such as off-air antennas, or digital sources such as satellites. The headend is also a typical location for early VOD deployments. As subscriber demand increases for VOD, however, it’s quite possible for VOD servers to be distributed in the network. The headend serves up video traffic to an Asynchronous Transfer Mode (ATM) or IP core network, which in turn feeds the access network, which will consist of DSLAMs and broadband digital loop carriers (DLCs). These devices provide the link to the IP set-top box, typically through a DSL modem.
A complete video solution will seamlessly deliver both video that may be viewed simultaneously by many users (multicast data in Figure 2, broadcast video in practice) and also video that is specific to a single user (unicast data in Figure 2, VOD in practice).
From an applications perspective, there are various functions that support – directly or indirectly – the residential service. Key ones already reviewed are the content processor and the VOD server.
Another important part is the electronic program guide (EPG), which is the TV directory data accessible via the set-top box. In addition, services like email and online gaming are now possible from the set-top box. To manage these applications, the telco needs a customer-relationship management (CRM) and billing application, and this has to interface with the existing back-office system. And a network management system capable of managing the digital video network is a key element. Finally, although this report doesn’t focus directly on voice services, the network is quite capable of offering second-line voice service by using VOIP (voice over IP).
But there is a simpler model, where the core network relies on Ethernet and IP alone (delivered over a DSL or FTTx access network). Connectivity to all devices is now via Ethernet, which is the simplest and the most cost-effective interface in the industry today. This is very important, because cost-effective bandwidth scaleability in the core is key in delivering VOD services. Remember that VOD is a unicast session between the video server and the subscriber's set-top box, which means that VOD will consume bandwidth at an alarming rate in the core.
However, multigigabit rings using coarse Wavelength Division Multiplexing (WDM) (CWDM) technology and 10-gigabit technology – when they become cost effective – can combat this problem. For quality of service (QOS) there is now a common QOS control plane, so the network can now implement techniques such as IP differential services (DiffServ) and VLAN class of service (COS) for specific application requirements.
So what are the technology enablers making video over IP happen?
Advances in compression algorithms have dramatically reduced the bandwidth requirements for delivering commercial-quality video. Compression rates today give between 3.5 and 4 Mbit/s per video stream, and in the future MPEG 4 will cut the bandwidth even more.
There are also new digital delivery techniques for content providers. For example, Digital Turn Around, which demultiplexes the Multiprogram Transport Stream coming from the satellite. Transcoding changes among different compression formats, and transrating cuts bitrates within a single compression standard. Such video processing techniques can be used at the headend to ensure proper content delivery to the network.
In this new world of IP video, telcos must pay close attention to security. Theft prevention is a must, and MAC address blocking, IP filtering, and authorization at the access level are required.
Internet Group Management Protocol (IGMP) has become a critical component in delivering video to the home, and the video set-top-box industry is standardizing on IGMP to control channel changing and hopping from the set-top box.
But the true enabler for video delivery is the advance in bandwidth and the latest generation of ADSL chips. With the new standards, such as S=1/2 and ADSL 2+, telcos can now deliver the bandwidth to meet commercial video requirements.