THE COMPLETE TECHNICAL PAPER PROCEEDINGS FROM: AN EVALUATION OF ALTERNATIVE TECHNOLOGIES FOR INCREASING NETWORK INFORMATION CAPACITY Ron Shani, Xtend Networks David Large, Consultant Abstract interchangeably with “information capacity” and “RF bandwidth” will be used when the HDTV, VOD, ITV and other applications historical meaning is intended). The are placing ever-greater pressure on increasing bandwidth demands fall into three operators to transport more information – broad categories: that which is widely distributed as well as communications with individual customers. 1) Common downstream (“broadcast”) Choosing how to create adequate capacity is bandwidth; that is, bandwidth occupied by difficult; driven by financial and regulatory signals that are transmitted throughout the constraints, capital costs and ongoing network (irrespective of whether or not operating considerations. individual customers are enabled to receive them). An example of common signals would This paper will evaluate some of the be a high-definition stream from HBO that technical options against those factors. would be continuously transmitted system- Evaluated technologies will include wide, but for which only certain subscribers bandwidth expansion to 1 GHz, more efficient would be authorized. modulation, more efficient video encoding, elimination of analog video carriage, splitting 2) Interactive downstream (“unicast”) of existing nodes, switched digital video and a bandwidth; that is, bandwidth occupied by proposed use of frequencies above 1 GHz that signals that are transmitted to individual offers the greatest bi-directional bandwidth customers. VOD, Internet communications expansion and the greatest benefit/cost ratio. and telephone are all examples of such signals. INTRODUCTION 3) Upstream bandwidth; that is, bandwidth occupied by signals that are transmitted from Bandwidth Pressures individual customers towards the headend. With the exception of a small amount of The history of cable television is one of bandwidth occupied by network element ever-increasing need for information capacity, management systems (NEMS), all upstream initially driven by the expansion of over-air signals fall in the same category as interactive broadcasting, then premium and ad-supported downstream bandwidth. satellite networks, followed by pay-per-view and high-speed data services. Today, The Case for Dramatic Bandwidth Increase operators are launching bandwidth-intensive high-definition television (HDTV) channels, Historically, manufacturers have offered various flavors of video on demand (VOD), cable operators increases in upper higher Internet access data rates, and downstream RF bandwidth limits in steps of telephone services. Each of these increases 50 MHz or so from an upper frequency limit the need for an increase in system information of 220 MHz to 860 MHz, with the upstream capacity (for purposes of this paper, unless bandwidth remaining fixed, except for one otherwise specified, “bandwidth” will by used step from 30 to 42 MHz. By contrast, in the data world, speeds have increased 4) Direct broadcast satellite operators will be exponentially over several orders of taking advantage of new spectrum, closer magnitude. As more content carried over satellite spacing, higher power and spot beam cable systems is digital in nature, more technology to realize greatly increased communications are directed to and from throughput – as much as 18,000 MB, or individuals, and competitors greatly increase enough to carry 2800 high-definition both video and non-video capacity, the programs at 6.5 Mb/s/program using question is whether operators will need to advanced codecs.iv significantly increase bandwidth, especially upstream bandwidth, to take advantage of 5) In general, television is moving from pre- opportunities and meet competition. scheduled broadcast of standard-resolution programs to on-demand presentation of high- A few points to consider: definition, with a 4X increase in bits per stream and the need to send programming to 1) On the competitive data front, SBC and (and receive communications from) individual Verizon, among other telcos, have launched a subscribers. Competitively, one satellite major fiber-to-the-curb/home push. Typical operator expects to offer its customers 150 of the technology to be deployed is Wave7’s national and 500 local HDTV channels by equipment which provides 500 Mb/s 2007 symmetrical data, shared among 16 passings, in addition to 860 MHz of RF downstream 6) Finally, upstream data communications bandwidth.i Verizon is offering data rates to rates from subscribers are increasing rapidly. 30 Mb/s downstream/5 Mb/s upstream in its VoIP is a symmetrical service; file sharing fibered markets, with the capability to offer can be symmetrical or even asymmetrical in rates of hundreds of megabits per second.ii the upstream direction; and near-future Some overbuild competitors in the US have services such as video telephony will require already offered 100 Mb/s service options to multiples of the bandwidth required for voice. customers and speeds of between 10 and 100 Comcast recently announced plans to offer Mb/s are commonly available in Asia. video instant messaging. RCN now offers a Finally, the capability of copper plant video surveillance service that allows continues to improve and now supports high- customers to stream video from up to four definition digital video. cameras through their broadband connection.v 2) Cable operators are already being pushed In summary, there is significant evidence to significantly increase rates – Comcast that cable operators will need major increases announced a standard rate of 4 Mb/s and an in bi-directional information capacity in the available 6-Mb/s downstream/768-kb/s near future, and that the upstream in upstream rate; Cox increased its standard rate particular, with a current capacity of only to 4 Mb/siii and RCN has upgraded its rates to about 100 Mb/s/node, is a major bottleneck 10 Mb/s. that will need to be addressed. 3) On the telephone side, the number of VoIP Operators can realize this increased residential and small business lines is information capacity through an increase in predicted to hit almost 11 million by 2008, RF bandwidth, through more efficient use of with a significant amount of that traffic existing bandwidth, or through more efficient carried over cable systems. sharing of existing bandwidth. Additionally, increased interactive bandwidth can be realized by sharing of the bandwidth devoted to interactive services among fewer fixing basic problems, while other systems customers. The various upgrade technologies may require little incidental preparation. that will be considered differ in their effects on broadcast verses interactive and Methodology downstream verses upstream information capacity, as will be seen. For ease of comparison, each technology was evaluated as a candidate for upgrading a Candidate Technologies hypothetical 100,000 home cable system which currently has 500-home nodes and an There are many approaches to generating average density of 100 homes per plant mile. more information capacity in a cable system. It is assumed to be 80% aerial plant. The This paper will evaluate the following connected household penetration is assumed possibilities: to be 70%, with 35% of connected homes equipped for digital video reception. The 1) An increase in downstream upper RF system is assumed to currently carry 80 bandwidth limit from 550, 750 or 870 MHz to channels of analog video, 136 total standard- 1 GHz. resolution broadcast digital video streams, 12 2) An increase in digital modulation density high-definition broadcast digital video from 256 QAM to 1024 QAM. streams, VOD, high-speed data, and VoIP. 3) Utilization of more effective digital video Unless otherwise stated, the system is compression technologies, such as MPEG-4. assumed to have been upgraded to 750 MHz 4) Subdivision of existing optical nodes. within the previous ten years. Other 5) Elimination of analog video carriage, with assumptions regarding the system will be the formerly-analog signals transmitted only discussed when relevant to each individual in digital form. candidate technology. 6) Use of switched digital video to avoid sending low-usage channels to subscriber Technologies were evaluated with respect groups except when requested. to their effect on both downstream and 7) Use of RF bandwidth above 1 GHz to upstream capacities and with respect to both expand both downstream and upstream commonly delivered (broadcast) and capacity. interactive services. In each case, the technologies were also evaluated qualitatively This is obviously not a comprehensive list, with respect to future enhancement options. and the choices are not mutually exclusive. Finally, conformance of each alternative to For example, an operator may choose to current regulatory requirements is noted. simultaneously increase modulation density and also use advanced digital compression INCREASE TO 1 GHz BANDWIDTH algorithms. For keep the matrix manageable, however, we evaluated each option separately. An increase in the upper downstream frequency limit to 1 GHz follows the When it comes to discussing quantitative traditional pattern of cable RF bandwidth results, we used what we felt were reasonable expansion. While it offers additional assumptions for an average cable system. For downstream capacity, it does not address the every possible upgrade scenario, however, the upstream bottleneck and does not offer a results will