VDSL - Swimming upstream
Business and residential subscribers are constantly demanding more bandwidth.
Historically the majority of this demand has been in the downstream direction, with users accessing content from the Internet. Now, though, users are generating copious amounts of content of their own explains Piyush Sevalia
Accompanying the trend in content creation are changes in network utilization and new applications that are now demanding greater bandwidth upstream-forcing carriers to swim against competitive currents in this same direction. Video serves as a good example. To compete with cable and satellite providers, many carriers are now offering Internet protocol television (IPTV), video on demand (VoD) and digital video recording (DVR), as well as additional value-added services that require greater upstream bandwidth. Plus, new bandwidth-hungry applications are certain to increase demand in the foreseeable future.
The leading technology for delivering higher bi-directional bandwidth is Very-high-bit-rate Digital Subscriber Line (VDSL), which has been standardised by the ITU-T as the VDSL2 standard. VDSL2 was designed to take full advantage of a carrier's broadband infrastructure with its increasing fibre optic capacity to the node, curb or building/basement. VDSL2 can deliver 100 Mbps symmetrical broadband bandwidth, which puts carrier services on par with LAN switching to the desktop.
Carriers around the world are experiencing tremendous success with their initial VDSL service offerings. As a result, most of these carriers are planning to add new or enhanced services to generate additional revenue streams, potentially as an upgrade to existing (and increasingly inadequate) legacy services.
Users, carriers and equipment vendors alike have a long history of underestimating the need for speed in order to keep costs under control. But the inevitable "forklift" upgrades are ultimately disruptive and costly.
Consider what has occurred in the local loop over the past couple of decades. Data communications in the public switched telephone network (PSTN) began with 300 BAUD modems, but was ultimately replaced with one that supported 1200 bps, then 2400, then 9600. A major breakthrough came with the advent of the 14.4 Kbps modem and then the really "fast" 28K modem. After a tweak to 33.6 Kbps, the modem reached its maximum potential with 56K technology. But even here, too, the initial asymmetrical V.90 standard was quickly replaced with a symmetrical version: V.92.
Despite these advances, users wanted more. Integrated services digital network (ISDN) offered great hope for the industry, but advent of digital subscriber line (DSL) technology began to erode ISDN market share. Some forms of DSL even began to supplant traditional T/E-carrier services, especially T1 and E1. Asymmetric DSL (ADSL) became the most popular rendition for consumers. But even ADSL has seen its fair share of changes - from ADSL to ADSL2 to ADSL2+ - all of which required a reinvestment in infrastructure.
Current access bandwidth compromises involve the upstream direction. The various versions of ADSL all deliver asymmetrical bandwidth and this lack of adequate upstream throughput is now becoming obvious in the marketplace.
Business subscribers were the first to recognise ADSL's limitations. The reason businesses need bandwidth symmetry is fairly straightforward: content. Organisations consume and generate a significant amount of content, requiring adequate bandwidth in both directions. Where fibre optic cabling is available to the premises, businesses often turn to DS-3 or Fractional DS-3 services. And where only copper is available, carriers have found it necessary to multiplex T/E1 or DSL services to meet the bandwidth demand.
Residential subscribers now feel the same pain. Although a vast amount of consumer-oriented content continues to reside outside the home on the Internet, the balance is changing as consumers generate their own content. Residential applications, detailed below, will require greater bandwidth in the upstream direction:
Home Networks: The home network is starting to resemble that of a small business, with multiple client PCs and a shared server. Multiple household members, all accessing the Internet requires higher bandwidth in both directions to ensure that the Internet experience remains acceptable.
Telecommuting: There has been dramatic increase in the number of people telecommuting full- or part-time. Creating an "office-like" work environment at home requires adequate symmetrical bandwidth for uploading content such as presentations and spreadsheets.
Peer-to-Peer (P2P) Applications: As traffic patterns go, P2P is driving consumer bandwidth usage worldwide, and is also causing bottlenecks. Asymmetric bandwidth is simply insufficient for many of these needs as the PC is both client and server. A University of Washington study concluded that P2P bandwidth dominates Internet bandwidth and contributes to its "peaky" traffic patterns. According to the study, the 24 per cent of Internet users who use P2P consume over 90 per cent of the bandwidth. The upstream bandwidth also is much higher than downstream bandwidth because users typically share audio and video files, which are much larger in size than data files.
Videoconferencing: As people have become accustomed to digital quality, most videoconferencing offerings have not been ready for consumer use because of poor image and sound quality. Adequate bi-directional bandwidth is the only remaining hurdle for carries to achieve high definition television (HDTV) quality videoconferencing.
Multimedia Messaging (MMS): MMS and other forms of instant messaging are standard applications today, but in the future they must become more robust to support video. Inexpensive built-in or add-on cameras allow users to send video-mail and video messages, or conduct a video chat session quite easily if they have sufficient bandwidth.
Video Monitoring/Surveillance: Affordable webcams enable users to "check up" on things from remote locations. In order to have decent video quality, the upstream data rate must be capable of being dynamically partitioned and sufficient to support the application.
Content Creation and Publishing: Blogs and video blogs are gaining in popularity, as consumers become Internet publishers. The trend toward "rich media" and full multimedia productions is resulting in an ever-increasing demand for upstream bandwidth.
Interactive Gaming: Home PCs owe much of their popularity to games and "edutainment" applications. As gamers seek new competition from around the world, they need additional bandwidth to ensure an uninterrupted gaming experience.
Remote Desktop Control: Many applications benefit from the ability to remotely control one PC from another. The complexity of PCs also now makes it beneficial for the Help Desk to have such access. Without bi-directional broadband bandwidth, this capability can be painfully slow and inefficient.
These new and emerging bandwidth-intensive applications, along with competitive pressures from cable and satellite providers, are forcing carriers to rethink their strategies. Newer technologies, especially hybrid fiber coax (HFC) and broadband wireless, threaten to undermine the inherent strategic advantage of a carrier's copper/fibre infrastructure. What carriers need is a robust bi-directional broadband solution that can be provisioned profitably for business and residential subscribers alike, and stand the test of time.
Most carriers are driving fibre deeper into their networks because new or enhanced, revenue generating services requires copious amounts of bandwidth. Fibre offers virtually unlimited bandwidth potential, and, as a result, is a rock-solid investment that will endure the test of time. But laying fibre to every single subscriber is difficult to justify financially-even in the face of increasing competition. Complicating factors of a fibre deployment include trenching driveways, drilling holes in walls, and setting up two-hour windows for appointments and then keeping them - all of which are an inconvenience to the consumer and increase time to revenue.
One DSL technology was designed to enable carriers to take full advantage of a fibre build-out: VDSL2.
VDSL2 technology delivers fibre-like bi-directional bandwidth over ordinary unshielded twisted pair wiring. Of all the DSL technologies available, VDSL2 is simply the fastest, delivering up to 100 Mbps in both the downstream and upstream directions.
This data rate (100 Mbps) is significant. Switched 100 Mbps is the predominant choice today for desktop connectivity in the LAN. The power of delivering the same 100 Mbps service in the access network represents a major breakthrough. For this reason, it will be a long time until VDSL2's potential bandwidth capabilities are exhausted.
VDSL2 can deliver ADSL2+-like connectivity to all subscribers and affords its highest level of performance to those subscribers closest to the carrier's central office (CO) or remote terminal (RT). With this robust rate/reach profile, carriers have greater flexibility to offer full broadband interactive services to offices and homes closer the CO/RT and basic Internet connectivity to consumers at longer distances. VDSL2 solutions are available in full-featured DSL access multiplexers (DSLAMs) or as remote gateways/concentrators that can be deployed either in the CO or RT. The customer premises equipment (CPE) is typically a single-port gateway or "modem" incorporating a DSL transceiver.
Carriers around the world are successfully deploying VDSL. These carriers include:
AT&T is just one service provider that is capitalising on existing copper infrastructure. For its U-Verse deployment, AT&T is building out fibre to the node (FTTN) and using VDSL2 to turbo-charge the existing copper loops entering homes. AT&T estimates that this architecture costs only about $360 per user to deploy - almost five times less than the cost of Verizon's all-fibre build.
Verizon and NTT, too, are using VDSL2 in a hybrid approach to deliver broadband services to multiple dwelling units (MDUs), such as apartment complexes or condominiums. In this scenario, they are using VDSL2 as the last mile technology because deploying fibre in restricted riser space is incredibly challenging.
NTT in Japan: NTT began deploying VDSL-DMT in 2002 with an initial asymmetric offering of 50 Mbps downstream and 11 Mbps upstream. Within a year or two, NTT rolled out two enhanced platforms: 50/30 Mbps and 70/30 Mbps upstream/downstream. In 2004, NTT added a 100/50 Mbps service. NTT subsequently deployed platforms that are capable of offering both 100/50 Mbps and 100/100 Mbps services.
AT&T in the US: AT&T is aggressively rolling out its U-Verse service based on VDSL technology in the last mile. U-Verse is part of the carrier's a $4 billion initiative to expand fibre optics deeper into residential neighbourhoods to deliver IPTV, voice and data broadband services.
Verizon in the US: Verizon is using VDSL2 to deliver high-performance, copper-based broadband services to multiple dwelling units (MDUs), such as apartment complexes or condominiums.
Belgacom in Europe: The Broadway project extends fibre infrastructure to street cabinets to over 14,000 nodes throughout Belgium. VDSL2 is a key technology in the Broadway project and enables Belgacom to offer revenue-enhancing triple play services, which include multiple simultaneous channels of high definition Internet protocol television (IPTV). Belgacom expects that its upgraded network will pass 60 per cent of Belgian households by spring 2008, enabling Belgacom to extend its market leadership by being the first carrier in Europe to announce high definition television (HDTV) service over VDSL2.
The lack of adequate upstream bandwidth has begun to place limitations on the types of services carriers can offer their subscribers. Fortunately, carriers still enjoy an inherent advantage over the competition: a basic infrastructure capable of cost-effectively delivering bi-directional broadband.
With VDSL2 technology, carriers have a more versatile and universal way to offer a wide assortment of new or enhanced-and quite lucrative-services.
A variety of VDSL2 DSLAMs, concentrators and gateways have been deployed in pilots or rolled out in full production networks. The day will eventually come when even 100 Mbps upstream and downstream is insufficient for many applications. But until then, carriers have a long and lucrative opportunity with VDSL and VDSL2.
Piyush Sevalia is Vice President of Marketing, Access Products Group, Ikanos Communications
Share this article with others
Post to del.icio.us
Printed from http://www.eurocomms.com/features/112208/VDSL_-_Swimming_upstream.html
Comment on this article
Skip to comments
We encourage users to analyse, comment on and even challenge European Communications's articles, including the one above - 'VDSL - Swimming upstream'
User reviews and comments that include profanity or personal attacks or other inappropriate comments or material will be removed from the site.
Additionally, entries that are unsigned or contain "signatures" by someone other than the actual author will be removed. We will take steps to block users who violate any of our posting standards, terms of use or privacy policies or any other policies governing this site.