Traditional telco carriers see tremendous revenue opportunities in the rollout of next-generation video services as part of “triple play” offerings, and they are gearing their networks to enable long-term, profitable growth in service adoption.

Today’s predominant video-distribution network topology—established primarily by cable companies or multi-service operators (MSOs)—was designed originally to support basic cable broadcast TV services. In this architecture, all analogue channels are broadcast to every customer over coaxial cable, and the channel to be viewed is selected in the TV set. Digital upgrades to the hybrid fiber coax (HFC) plant in recent years have allowed MSOs to introduce digital broadcast channels, high-definition TV (HDTV), broadband Internet and, most recently, video on demand (VoD) and voice over Internet Protocol (VoIP) for complete triple play solutions.

Except when serving customers with fiber-to-the-premises (FTTP) access, this broadcast model of video distribution is unsuitable for traditional carriers looking to leverage the ubiquitous last-mile copper plant for video services. Digital subscriber line (DSL) technologies have been deployed for video services and are migrating to support increasingly higher speeds with Very High-Speed DSL (VDSL) as fiber is extended closer to the end user. DSL access requires a Switched Digital Video (SDV) approach for Internet Protocol TV (IPTV), which is carried over the same medium as broadband Internet and voice services for the triple play solution.

Key to all of the triple play offerings is the need to backhaul large amounts of bandwidth cost-effectively and reliably across the metro network to service and content termination points. The emerging “Optical+Ethernet” network framework provides a powerful yet flexible underlying foundation for supporting the range of network options. As simple and stable as legacy transport infrastructure, Optical+Ethernet solutions enable carrier-class, standards-based delivery and management of next-generation video services. The optical transport layer leverages Wavelength Division Multiplexing (WDM) and Reconfigurable Optical Add/Drop Multiplexer (ROADM) technology with control plane for scalability and transparency; the integrated aggregation layer is based on Ethernet for flexibility, intelligence and efficiency. These are the technological building blocks upon which carrier and MSO networks around the globe are being built.

Last-mile Ramifications

With DSL access, the last-mile bandwidth is less than the total broadcast bandwidth of offered channels. To provide broadcast-equivalent service to the end user, SDV or IPTV is needed, where only the TV signals being watched are delivered over the DSL link at any one time. As different channels are requested at the TV’s set-top box, a DSL access multiplexer (DSLAM) works behind the scenes to switch channels, which are then multicast (rather than broadcast) to all requesting viewers subtending from that DSLAM. Further upstream signaling must take place in the network to ensure the DSLAM has access to all channels, and it, in turn, will be part of a multicast group receiving particular channels.

This contrasts with FTTP deployments, where the fiber bandwidth is larger than the broadcast bandwidth. The carrier has the means—and luxury—to implement the traditional broadcast model pioneered by the MSOs, with video content being delivered over a separate wavelength of light across the optical fiber.

We should expect, however, a migration toward IPTV for all of the last-mile approaches deployed by MSOs and telcos. There are improvements in bandwidth efficiency to be achieved (particularly important as the amount of content increases), as well as the means to personalize content and advertising to the end user depending on viewing usage.

With the existing last-mile approaches and the expected migration, what then should be expected from the backhaul and transport network?

Growth of Ethernet

Carriers and MSOs alike find themselves at the confluence of a variety of important business and technological trends:

The diverse demand for services—Business customers seek a range of mission-critical services such as high-speed virtual private networks (VPNs), business continuity, disaster recovery, business-to-business and business-to-consumer e-commerce. Consumer customers seek services such as high-speed Internet, video distribution, VoD, video conferencing and online gaming. To profitably accommodate ongoing growth in demand across business and consumer customer segments, service providers must enable the range of services without driving up costs through network overlays.

The video bandwidth crunch—Video services consume a large amount of bandwidth in the network: typically 3Mbit/s per standard definition (SD) channel and 18Mbit/s for each HD channel with MPEG2 encoding today. (MPEG4 may be used to gain up to two-times improvement in bandwidth efficiency for new network deployments.) For on-demand, unicast services, the total network bandwidth demand increases linearly with the number of concurrent users. Unlike broadband Internet, only limited benefits can be achieved from statistical multiplexing due to the continuous video data stream.

The drive to collapse networking layers—The Synchronous Optical Network (SONET) layer has historically shouldered transport, but the parallel operation of multiple overlay networks and topologies drives high capital and operational expenses (CAPEX and OPEX) for service providers. To achieve cost reductions they require—and at the same time simplify topologies and build scalability—service providers believe they must migrate from SONET to converge IP, Ethernet and Multiprotocol Label Switching (MPLS) on WDM-enabled optical networks.

The emergence of Ethernet-transport standards—Standardization underway in the Internet Engineering Task Force (IETF), The Institute of Electrical and Electronics Engineers (IEEE) and International Telecommunication Union-Telecommunication (ITU-T) is enabling circuit-like Ethernet transport with improved operations, administration and maintenance (OAM), manageability and service differentiation.

These trends are leading carriers and MSOs alike to adopt the emerging Optical+Ethernet network framework for backhaul and transport across the network. Combining optical and Ethernet technologies provides a seamless, commonly managed, highly scalable and cost-effective capability for video distribution.

MSO Video-distribution Topology

Figure 1 shows a representative MSO network architecture for video distribution and triple play services characterized typically by a flat core transport layer supporting multiple hub sites with HFC termination.

Figure 1: HFC Broadcast Model for Video Distribution

Broadcast video traffic is duplicated downstream to each hub node. On demand, broadband Internet and voice services are served by unicast connections from hub sites to the head end. Highly asymmetric traffic patterns (downstream/upstream) lead to consumption of bandwidth in each direction around rings for maximum efficiency. Cable-modem termination systems and edge quadrature amplitude modulation (QAM) termination equipment interface the HFC plant. Thousands of homes may be connected to one hub site.

A key requirement is to efficiently aggregate Ethernet traffic from a large number of sites to the head end—the location for on-demand content storage and local content injection. In an Optical+Ethernet implementation for MSO video distribution, WDM provides the inherent transport scalability and intelligent Ethernet transport that the MSO requires—as well as the ROADM functionality for dynamic setup, reconfiguration and balancing of wavelength connections, via software control.

Serving Customers via FTTP

We have also seen the broadcast model used in rolling out video services to customers via FTTP. Without the bandwidth limitations of copper-based access media, carriers gain the luxury of broadcasting all video channels directly to their subscribers over FTTP using a separate wavelength overlay. This approach is different in physical media type but similar in terms of connectivity.

Moving forward, however, even this newly deployed FTTP model is headed toward a more efficient distribution paradigm. An IPTV, multicast approach would enable a single wavelength to be used for all IP traffic—be it broadband Internet, VoIP or video—rather than two separate wavelengths for data and video. Cost savings will, thus, occur in the FTTP equipment at the customer premise and the serving office. Further, usage intelligence provided by the IPTV approach will provide new advertising and content-targeting opportunities.

Adopting a More Efficient Model

Figure 2 shows a classic carrier network solution based on fiber to the node (FTTN) with DSL last-mile distribution for next-generation services. Typically, the network consists of an aggregation layer and core transport layer for scalability. In the access/aggregation layer, subscribers are linked to IP DSLAMs via copper pairs, and traffic is then aggregated with Coarse/Dense WDM (CWDM/DWDM) links to core nodes. In the core transport layer, traffic is further aggregated and transported to the metro hub location where broadband services routers (BSR) provide service management, local content injection and interface to the IP/MPLS network for video content and Internet connectivity. Among DSLAMs, routers and transport equipment, Ethernet is becoming the ubiquitous interface.

Figure 2: IPTV Multicast Model for Video Distribution

This model for video distribution relies on multicast connections, rather than broadcast. Channels are sent downstream from the BSR location to DSLAMs, and then on to the subscriber based on the subscriber request. Channels are, thus, multicast to all viewers requesting the same content. Multiple DSLAMs are connected to WDM transport equipment, so this equipment must also be capable of supporting multicast connections with the means to add/delete connections based on demand. As the amount of programming increases, the possibility of all content being needed at each DSLAM location decreases; in this way, the multicast model can be seen as increasingly efficient.

Optical+Ethernet provides benefits of convergence and scalability. In support of the usage-aware IPTV environment, however, Optical+Ethernet solutions also provide support for multicast functionality.

The Flexibility of Optical+Ethernet

The multicast method of video distribution—mandatory if serving customers via copper-based DSL—is also of interest to providers serving customers via coaxial cable or fiber access. Optical+Ethernet provides the ideal framework for support of broadcast or multicast video distribution approaches and seamlessly enables migration.

Optical+Ethernet provides the right attributes for the triple play solution. WDM scales easily for increased capacity to meet the needs of the video bandwidth crunch. Flexible optical configurations provide cost-per-bit optimization in a range of deployment scenarios, including ROADMs with control plane for metro core networks. Rapid protection against failures and low latency are especially important benefits for VoIP applications. Efficient Ethernet aggregation and intelligence support a range of connection types and efficient bandwidth usage. With Optical+Ethernet solutions, intermediate SONET layers are eliminated, capital expense reduced and management of the network simplified.

Finally, Optical+Ethernet solutions deployed for consumer triple play services provide a common infrastructure for business services such as VPN, VoIP, high-speed Internet access with integrated demarcation capabilities for assurance of service-level agreements (SLAs) and OAM functionality for maximum service availability.

Conclusion

Despite important differences in the way their video-distribution networks manage content, traditional telco carriers and cable MSOs are trying to achieve the same customer experience—high-quality video, seamless channel surfing, etc. They are also trying to achieve the same business benefits with these video-distribution networks, namely profitable rollout of next-generation services to mass-market audiences.

The emerging Optical+Ethernet framework—capable of supporting the alternate models of video distribution—ultimately creates a future-safe network with obviated investment risks for supporting the range of next-generation consumer and business offerings. Optical+Ethernet transforms the carrier or MSO network into a long-term competitive advantage.

Paul R. Morkel is director, business management, carrier WDM, with ADVA Optical Networking (www.advaoptical.com).