[opendtv] Gigabit PON for HDTV
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 15 Aug 2004 17:53:37 -0400
This is an interesting article. When you buy broadband service, your PC thinks it is connected to the Internet via a standard IP-over-Ethernet interface. But the actual connection may actually be DOCSIS, ATM over ADSL, ATM over SONET, or any of a bunch of other schemes. The router you get from the service provider converts any of these to IP/Ethernet, for the convenience of your PCs. (And you may also get regular old telephone service as a frequency- divided channel, if you subscribe to an ADSL service.) Well, as I've suggested previously, transmitting DTV over the MPEG-2 TS scheme used by DTT, digital cable, and DBS, is not a bad way to go. It's a viable approach that is already a standard, and therefore easier to implement than something different. Just like the PC example, if the box you get from an optical service provider could convert whatever to MPEG-2 TS over 6 MHz channels, then the future built-in tuners would work just fine even for this new TV-from-the-telco service. This article goes one (controversial) step further. It suggests that in a future gigabit passive optical network (GPON), separate optical wavelengths could be dedicated to carry an exact replica of the TV distribution RF channels. Shades of the POTS service along with ADSL. I don't think it's essential to do it this way, but their heart is in the right place, as it were. Bert ------------------------- PON trio grabs at triple-play services By Robert Keenan , EE Times August 05, 2004 (11:27 AM EDT) URL: http://www.eet.com/article/showArticle.jhtml?articleId=3D26806106 The long-sought quest to bring home three services - voice, video and data - in one big, fat optical pipe may boil down to a game of PONs. But even as telecom providers get their feet wet in passive optical networking, the field's technology choices are multiplying, with carriers pondering the relative merits of broadband, Ethernet and, now, gigabit PONs. That interest is at a high pitch can be seen in the recent flurry of requisitions for passive-optical-networking equipment. Verizon, for example, recently said it was investing $800 million in PON deployments this year, while BellSouth announced in June, at the Supercomm trade show, that it would spend $6 billion over the next few years for PON implementations. For its part, NTT in Japan has already chosen infrastructure providers for its planned PON deployment and is in the process of selecting suppliers of customer premises equipment. In the access market, PONs - essentially last-mile fiber connections that are used to deliver consumer broadband services - are seen as a clear entry strategy for incumbent telecom carriers to take their triple-play services the last mile to the customer's home. ("Passive" simply describes the fact that optical transmission has no power requirements or active electronic parts once the signal is going through the network.) Of the trio of voice, video and data, many telcos put video first and view PONs as a means to start stealing business from their archrivals in the cable communications sector. With their hefty data rates that leave DSL in the dust, PONs are also seen as a way of moving toward a converged network - a move that could finally solve network-management headaches. For the most part, the initial PON deployments have focused on two technologies: broadband, or BPON, an ATM-based system that has garnered attention in the United States, and Ethernet, or EPON, an Internet Protocol-centric system that is based on specifications being developed in the IEEE 802.3ah committee. But even as EPON and BPON get their first footholds in the sector, another technology, gigabit PON, is making its presence felt. Indeed, some industry observers are predicting great things for GPON, which pushes downlink performance into the 2.5-Gbit/second range, from 622 Mbits/s in BPONs. GPON brings two key advantages to the design community. The first is the implementation of a new framing mechanism that is drawing accolades around the industry. The generic encapsulation method (GEM) lets designers carry both Ethernet and time-division multiplexed (TDM) traffic natively on a GPON link. "ATM can be natively handled on a GPON link," said Didi Ivancovsky, vice president at Israel-based PON chip set developer BroadLight. But going forward, many carriers are as interested in carrying both TDM and Ethernet traffic. GEM enables them to do so. The second, and most talked-about, benefit is fatter uplink and downlink pipes. Currently, BPON systems support downlink performance of 155 or 622 Mbits/s and uplink performance of 155 Mbits/s. An optional BPON mode some developers are looking at moves downlink throughput into the 1.25-Gbit/s range. GPON pushes performance in both directions into the gigabit range. Specifically, the G.984 specification defines GPON downlink speeds of either 1.25 or 2.5 Gbits/s and uplink speeds at 155 Mbits, 622 Mbits, 1.25 Gbits or 2.5 Gbits. Whichever way you slice it, both represent big leaps over existing BPON systems. Is it needed? One logical question designers must wrestle with is whether there is a strong need for 2.5-Gbit bandwidth. The answer to that question lies in the delivery of video services. While some industry players think current BPON systems can adequately support video, many believe it will not have the horsepower to handle the emerging demand for switched-digital video and high-definition television (HDTV) being asked for by carriers. Current BPON systems rely on a low "split rate" to deliver services to customers - 6:1 is a number many throw around. The split rate tells how many customer premises systems are connected to a central office. Traditionally, higher split ratios lead to more efficient broadband networks but also result in lower data rates delivered to a customer. In the case of PON systems, carriers are expected to to push their split rates into the 32:1 or 64:1 range. Since data rates will decrease at those higher split rates, it could be tough for BPON systems to support HDTV going forward, BroadLight's Ivancovsky said. Antpi Kankkunen, vice president of product strategy at Tellabs Inc. (Naperville, Ill.), agrees that BPON will have trouble with high definition. "The driver for going to GPON will be the deployment of HDTV services," Kankkunen said. Indeed, thanks to the rate increase, "GPON is a bit more appealing than BPON," said Sayeed Rashid, senior marketing manager at Alcatel. "It's a bit more suitable for high-bit-rate applications." The issue of video, however, runs deeper than just bandwidth. Currently, the BPON specifications define a separate lambda that designers can tap to provide an RF overlay for handling broadcast video traffic. The International Telecommunication Union has included support for an extra lambda in the GPON specification as well in order to continue the support for an RF overlay or video. But with the increased data rates, GPON also provides the ability to support Internet Protocol (IP) TV services, raising the question of whether it makes sense to support an RF overlay for carrying video in the GPON world. "You can do anything you can do with satellite and cable using the RF overlay," Alcatel's Rashid said. "GPON equipment vendors will have to support it." On the contrary, said Michael Howard, principal analyst at research firm Infonetics Research (San Jose, Calif.). "There is no value in the RF overlay in GPON deployments." Moreover, GPON boxes implementing this overlay will be "too expensive," he added. Howard also said that the RF overlay doesn't play well with the carrier push for fewer networks. "So why keep the legacy around at all?" In Howard's view, "When the GPON market arrives, carriers are going to go to converged networks." Although others have said that IP-over-TV makes sense ultimately, cost issues will be one driver for keeping the RF overlay intact as GPON technology starts hitting the market. While IP set-top boxes are emerging, most of the set-tops in the market today still reply on a copper coaxial connection. Thus, to go all-IP, carriers will have to make a significant investment in new set-top designs. And according to ECI Telecom's Aviv Ronai, that can add up to 30 to 50 percent increases in capital expenditures. "New STBs are a major investment," said Ronai, who serves as assistant vice president of marketing for ECI's broadband division. "Carriers are trying to avoid that capex cost now." Opinions vary on the importance of an overlay, so in reality the decision whether to implement an overlay will likely vary from carrier to carrier. "Carriers have yet to decide how video is done," Alcatel's Rashid said. "We're all looking at all of the possibilities," said Timothy Flood, senior director of product line management at AFC Inc., a Petaluma, Calif., PON and broadband equipment provider. Rolling it out To date, only two companies - Optical Solutions and Flexlight Networks - have developed GPON systems for carrier deployment. No other BPON manufacturers have yet rolled out gigabit PON equipment, raising questions about whether GPON is ready to replace BPON in real-life deployments. Things could start changing quickly on the equipment front, however. AFC, Alcatel, Ciena, ECI, Lucent and a host of other manufacturers are looking at ways to upgrade their central-office PON solutions to support GPON operation. "GPON is just a card swap-out," said Gary Bolton, vice president of product marketing in Ciena Corp.'s Broadband Access Group. "It's an OLT [optical-line terminal] blade." Lucent Technologies Inc. plans to add GPON to its Stinger DSL access concentrator platform. "We're going to take Stinger and put PON on it," said Will Engler, vice president and general manager of Lucent's Access Networks division. "We're looking heavily toward a GPON implementation." Chip set vendors are also stepping up to help OEMs make GPON come to life. Ivancovsky said BroadLight expects to have a GPON chip set available by the end of the first quarter of 2005. Existing BPON chip set players Freescale Semiconductor and Centillium are also working on GPON offerings. Centillium has said it expects to have a GPON solution in the second half of next year. Freescale remained mum on a specific time frame but did say that chip sets could hit the market as early as 2005. "We are working on GPON as a natural outgrowth of PON market demand," said Niket Jindal, business development and marketing manager at Freescale Semiconductor. On the carrier side, existing BPON players, like Verizon, will continue down this path until GPON systems are readily available. Other carriers, such as Bell Canada, have already made the commitment to GPON. But there are still a number of carriers that have not yet picked their PON, especially in markets such as Europe. If equipment is available and they can wait, most industry watchers believe that GPON will be a better option than BPON for these undecided carriers. "I suspect some carriers will wait for GPON," Infonetics' Howard said. 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