IPTV, or TV services delivered over a managed IP (Internet protocol) network, is expected to skyrocket in the next five years from four million subscribers in 2006 to a projected 103 million in 2011 according to a recent report by analyst firm iSuppli Corporation (Figure 1). IPTV is the highest bandwidth service ever deployed into the network.
Along with the rapid increase in subscribers, there are two amplifying trends that will pose significant challenges and opportunities to network designers: video-on-demand (VoD), and the shift to high-definition TV (HDTV).
Figure 1
IPTV covers both live TV and stored video. VoD usage today in IPTV systems is a paltry seven percent, meaning that 93 percent of content is broadcast. As service providers continue to roll out time-shift functionality, also known as network digital video recording (DVR), this penetration for video-on-demand should increase from seven percent to 70 percent or higher. As users shift from watching broadcast TV to VoD, this shift will drive a tenfold increase in the bandwidth used required in the core network.
At the same time, users are shifting towards HDTV. These signals require four to eight times more bandwidth than standard definition to accommodate the increased resolution of the signal. High-definition penetration in 2006 was 15 percent (Consumer Electronics Association) and is forecast to grow to 60 percent over the next five years. This implies at least a fourfold increase in network bandwidth simply to accommodate this migration.
Taken together, these three trends (increasing IPTV penetration, VoD usage and a migration towards HDTV) mean that the network bandwidth used by IPTV will increase a staggering 1000 times, or 100,000 percent. This rapid growth presents network designers with a set of architecture and design challenges that must be addressed in order to allow cost-effective, high-quality video deployments. IPTV vs. TV over the Internet ” the same thing?
The terms IPTV and Television over the Internet are often used interchangeably but refer to two different technologies.
TV over the Internet, popularized by YouTube, is video clips delivered over the Internet to consumers who watch it on a PC. The display is usually a small window on a monitor, and the video may or may not play smoothly depending on the quality of the Internet connection. TV over the Internet is typically used to watch short video clips and is not positioned as a replacement for broadcast TV. In contrast, IPTV is broadcast-quality TV, intended to compete directly with cable or satellite operators. IPTV is typically offered over DSL or a fibre-to-the-home (FTTH) network, and is offered by the carrier (usually the local phone company) who owns the network.
IPTV systems normally include an IP set-top box (IP-STB) that sits beside the TV and converts from IP to video signals. It is the combination of the IP-STB and managed network that provide the user with the same experience as possible through cable or satellite and allow the phone companies to compete for TV services.
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IPTV Architectures
Only three network elements are required for a minimalist IPTV implementation: video encoders to convert from broadcast TV to IP packets, an access network to connect subscribers to their service provider and a set-top box to convert from IP to video at the subscriber premise. More typical networks include several additional systems: VoD servers, ad insertion systems, billing platforms and Digital Rights Management (DRM) systems. A typical IPTV system is shown in Figure 2.
Figure 2: Typical IPTV System Architecture (simplified)
There are two variants to deliver broadcast and VoD streams over the “last-mile” from the central office to the subscriber.
“Pure” IPTV systems deliver all channels, both broadcast and VoD, over IP through the network to the subscriber. This is the architecture used by DSL providers and some of the FTTH providers. In this architecture, the broadcast channels are sent as multicast streams from the video encoding units to the head-end DSLAMs, which pick out the specific channels being watched by each subscriber and send only those channels down the DSL link towards the subscriber. VoD streams are handled the same way, and flow down the DSL link beside the multicast broadcast channels.
“Hybrid” IPTV implements RF-encoded video for the broadcast channels and IP streams for VoD. Fibre deployments often use hybrid architectures, with one wavelength of light carrying the video signals and a separate wavelength used for the IP traffic. In hybrid architectures, an Optical Network Terminal [ONT] at the subscriber premise is needed to convert from fibre to TV and Ethernet.
Bandwidth Requirements
IPTV is practical only because of the staggering compression levels that are possible with modern video codecs, as video streams can be compressed more than 100:1 using the latest MPEG-4 (H.264) codec. Even with this level of compression, IPTV is easily the highest bandwidth service ever mass-deployed into the network. A single hour of IPTV requires five Gigabytes, the same as 1,000 hours of voice and more than the annual amount of email a consumer will receive and send.
A single video stream consumes between 1.6 Megabits/s [Mb/s] and 12 Mb/s depending on the encoding method and whether the stream is standard definition (SD) or high definition (HD). The table below shows typical bit rates:
Table 1
One of the defining hurdles for broad IPTV deployment has been the ability to support multiple video streams over a DSL line. As shown in the table, MPEG-4 achieves roughly twice the compression as compared to MPEG-2 and makes it easier to support this goal.
The second part of the solution has been the continued development of the DSL standards and the additional bandwidth available from advanced DSL variants. VDSL2 and ADSL2+ can provide 10 to 25 Mb/s of bandwidth depending on the length of the local loop while 15 Mb/s is possible to the majority of DSL subscribers in North America using these new standards.
However, since the average American home has 2.5 TV sets, the network designer must plan for three or more TVs per subscriber. In addition, the network designer must decide whether to support digital video recorders at the subscriber household. Many DVRs can record two programs simultaneously, increasing the bandwidth requirements.
In an extreme case, for a subscriber with two HDTVs and DVRs and a third SD TV, 26 Mb/s can be required for IPTV alone, with any amount for residential broadband or phone service on top of this. This level of bandwidth can only be delivered to subscribers with a very short loop length, not as a broadly deployable solution.
One way to cut the bandwidth requirements down is to provide DVR functionality at the central office instead of at the subscriber level. With a centralized DVR, each TV only needs a single channel and the required bandwidth is down in the 10 to15 Mb/s range, within the capabilities of ADSL2+ and VDSL2.
10GbE Usage in IPTV
The bandwidth required by IPTV makes it a good match for 10 Gigabit Ethernet. A broadcast-only system can squeak by with Gigabit Ethernet; 200 SD channels and 100 HD channels can be squeezed into a single Gigabit Ethernet pipe with the advanced codecs, but as VoD streams are added, 10 Gigabit Ethernet provides a welcome solution to the proliferation of Gigabit Ethernet cables. As described above, a single household may consume 20 Mb/s with multiple streams; hence, a Gigabit Ethernet link can handle only about 40 subscribers while a 10 Gigabit Ethernet link can handle 400 subscribers. As VoD or network-based DVR functionality is rolled out into the network, 10 Gigabit Ethernet will be used more and more broadly.
The declining cost of 10 Gigabit Ethernet components has accelerated the shift towards 10 Gigabit Ethernet. 10 Gigabit silicon can now be obtained for less than $100 per port, and the optical transceivers, the highest cost portion of the system, are dropping dramatically in price. A new standard for these optical modules, SFP+, is responsible for much of the drop, with SFP+ transceivers being less than one-third of the cost of XFP modules.
10GbE System Designs
The first step in a high capacity system design is to map out the data flows through the system, and critically, to decide how high availability will be handled, as these decisions affect every element of the system design. In the case of IPTV, the data flows can be complex, as they are normally a combination of multicast (broadcast TV) and unicast (video-on-demand) streams, with both high bandwidth video streams and low-bandwidth control traffic. Once the data flows and high-availability models have been created, a platform must be selected. This platform can be custom designed to meet the specific application, or an open platform can be adopted. In the past, this was an easy decision as there were no open platforms with the capacity or reliability required for IPTV and other high bandwidth applications, but open standards-based platforms for 10 Gigabit processing are now available. The Advanced Telecommunications Architecture (ATCA) is the leading open standard that provides 10 Gigabit Ethernet on the backplane, providing enough capacity to implement many of the IPTV network elements.
A complete platform for IPTV requires switches, packet processing blades, CPU cards and a high-availability software, all capable of 10 Gigabit Ethernet speeds. One example of such an ATCA platform is the Continuous Computing 10 Gigabit Traffic Management and Security Platform, which features high-performance packet processing and system optimizations to allow up to 120 Gigabits/s of throughput.
At the heart of the platform is the FlexPacket PP50 – a high performance 10 Gigabit packet processing blade. The FlexPacket PP50 uses two of the Raza Microelectronics XLR732 packet processors to allow for highly programmable, high-complexity packet inspection and classification (Figure 3).
Figure 3
Video Traffic Shaper & Quality Monitor
One of the requirements for high-quality video is a tightly managed network that provides good quality-of-service (QoS) for the video packets. In most IPTV deployments, other services like Web traffic, email and peer-to-peer downloads are flowing over the same IP connections, which can make it a challenge to ensure that the video packets are not disrupted.
One solution is to monitor and shape the traffic to ensure that the non-video traffic does not interfere with the video traffic. To maximize effectiveness, the shaping platform should be deployed as close to the subscriber as possible, typically between the DSLAM and the core network. Figure 4 shows an implementation of an 80 Gb/s shaping platform in ATCA capable of serving 4,000 subscribers at 20 Mb/s per subscriber. This implementation uses the Continuous Computing FlexPacket PP50 packet processing blade to inspect and classify packets, and to shape the packets based on the traffic class of each packet.
Figure 4
The PP50 provides the capability to inspect every packet at 10 Gigabit/s. The blade can classify a packet into a particular traffic class: video, VoIP, web, email or peer-to-peer, but examining headers, port numbers and payload. The PP50 can support hundreds of thousands of traffic flows and millions of packets per second with high-speed header lookups in a TCAM (ternary content addressable memory), specifically designed for traffic classification.
Once the traffic has been assigned to a specific class, the PP50 can take a variety of actions: it can restrict a class of traffic to a certain limit, reprioritize packets to ensure that video and voice traffic flows without interruptions while bulk traffic like peer-to-peer is restricted, or even drop particular kinds of traffic. In addition, the PP50 can monitor each class of service so that network architects can understand bandwidth usage per application and per subscriber.
With thousands of subscribers supported in a single chassis, high availability is a key requirement. This platform implements high availability through 1+1 redundancy of the switches, and N+1 redundancy for the packet processing blades. This combination of 1+1 and N+1 redundancy allows for cost-effective high availability.
What’s Ahead
IPTV appears to be the killer application for network bandwidth consumption and equipment procurement. The projected twenty-fold increase in subscribers over the next five years, coupled with a swing towards time-shifted TV and high definition, means that IPTV could consume 1,000 times more bandwidth than is consumed today.
This dramatic increase demands innovative solutions, and standards-based ATCA platforms provide an ideal mechanism for implementing IPTV services. The scalability, high bandwidth and broad ecosystem of ATCA enable rapid time-to-market while leaving substantial room for innovation and differentiation.
