When the U.S. RBOCs and Japan's NTT issued request for pricing (RFP) for passive optical networking (PON) equipment, the promise of delivering last-mile optical connections to residential customers started to become a reality. And, as 2004 kicked off, the market got promising as carriers began to make promises and take action. Verizon said recently it is investing $800 million in PON deployments this year. NTT has already selected infrastructure providers and is in the process of selecting customer premise equipment providers for its planned PON deployment. And, BellSouth said at Supercomm that it will spend $6 billion over the next few years for PON deployments
For the most part, the initial deployments of PON networks have focused on two technologies. The first is broadband PON (BPON), an ATM-based system that garnered quite a bit of attention in the U.S. The other is Ethernet PON (EPON), an IP-centric system that is based on specifications being developed in the IEEE 802.3ah committee.
But, as EPON and BPON just start to gain hold in the sector, another technology, called gigabit PON (GPON), is starting to rear its head in the sector at the evolutionary path for designers embarking down the BPON path. And with specs ironing out and BPON still not in mass deployment, some are wondering whether GPON, which pushes downlink performance into the 2.5-Gbit range, may be the right option for PON deployments going forward.
Why all the hubbub?
Clearly, the rollout of PON systems in the access market is seen as a clear entry strategy for existing incumbent telecom carriers to provide triple-play servicesvoice, video, and data to the home. While triple-play is a nice word, in reality, many of the telcos are viewing PONs as a means to offer video services and, in turn, start stealing away business from their arch rivals in the cable communication sector. They also see PONs as a means for moving to a converged network, a move that could finally solve network management headaches
One of the reasons that PONs are so attractive is due to the data rates they provide. While a DSL or cable connections can offer tens of megabits in the downlink path, current PONs can offer anywhere from 155-Mbit/s to 1.25-Gbit/s throughputs in the downlink path. For example, BPON systems can deliver 155- and 622-Mbit/s downlink streams while EPON systems are designed to deliver 1.25-Gbit connections.
To date, the discrepancy between the performance of EPON and BPON has been one of the big debates in the access space. Particularly, many have wondered whether the 622-Mbit downlink performance provided by a BPON system provides enough horse power to support the deliver of HDTV services to end customers.
To address this concern, the ITU-T committee set out to define a set of specification that will provide an evolutionary path for the BPON community into the gigabit performance range. From those efforts, the committee has defined the G.984 specifications, which define GPON operation.
Across the board, industry members agree that GPON provides two key advantages to the design community. The first is the implementation of a new framing mechanism that is catching accolades around the industry. The framing mechanism, called the generic framing method (GEM), allows designers to natively carry both Ethernet and TDM traffic on a GPON link.
"ATM can be natively handled on a GPON link," said Didi Ivancovsky, vice president at PON chipset developer BroadLight. But, going forward, many carriers are as interested in carrying TDM and Ethernet traffic. "With GEM, designers can encapsulate native TDM and Ethernet traffic on a GPON frame."
The second and most talked about benefit is increased uplink and downlink. Currently, BPON systems support downlink performance of 155- or 622-Mbit/s and uplink performance of 155 Mbit/s. An optional BPON mode, which is being looked at by some developers is also available that moves downlink throughput into the 1.25-Gbit/s range.
GPON moves performance in both the uplink and downlink into the gigabit range. Specifically, the G.984 specification defines GPON downlink speeds of either 1.25 or 2.5 Gbit/ and uplink speeds of either 155 Mbit, 622 Mbit, 1.25 Gbit, or 2.5 Gbit, both big leaps over existing BPON systems.
Increased bandwidth: Do we need it?
One logical question that designers must wrestle with in regards to GPON is whether or not there is a strong need to push bandwidth to 2.5 Gbit/s. The answer to that question lies in the delivery of video services. While some industry members feel that current BPON systems can support video services, many feel that BPON will not have the horsepower to support the emerging demand for switched-digital video and high-definition TV (HDTV) being asked by carriers.
Current BPON systems rely on a low split rate to deliver services to customers6:1 is a number many throw around. Going forward, however, carriers will look to push that split rate into the 32:1 or 64:1 range. And, as BroadLight's Ivancovsky pointed out, at these higher split ratios, BPON rates will decrease, making it tougher to support HDTV.
Tellabs Vice President of Product Strategy Antpi Kankkunen agrees that BPON will have trouble with HDTV. "The driver for going to GPON will be the deployment of HDTV services," Kankkunen said.
Because of 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," he added.
To overlay or not: That's the question?
The issue of video, however, runs deeper than simply a bandwidth question in the GPON world. Currently, the BPON specifications define a separate lambda that designers can tap to provide an RF overlay for handling broadcast video traffic. The ITU has also included support for an extra lambda in the GPON specification in order to continue the support for an RF overlay or video. But, because of the increased data rates, GPON also provides the ability to support IP TV services, raising the question about whether supporting an RF overlay makes sense for carrying video in the GPON world.
"There is no value in the RF overlay in GPON deployments," said Michael Howard, principal analyst at research firm Infonetics Research. GPON boxes implementing this overlay will be "too expensive," Howard 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? When the GPON market arrives, carriers are going to go to converged networks," Howard added.
Howard isn't alone in his opinion. Other members have said that ultimately IP over TV makes sense. But, members of the sector also said that cost issues will be one driver for keeping the RF overlay in tact as GPON technology starts hitting the market.
While IP set-top boxes are starting to emerge, most of the STBs in the market today still reply on a coaxial connection. Thus, by going all IP, carriers will have to make a significant investment in new STB designs, which ECI Telecom's Aviv Ronai said can add 30 to 50 percent increases in capital expenditures.
"New STBs are a major investment," said Ronai, who serves as assistant vice president of marketing in ECI's broadband division. "Carriers are trying to avoid that capex cost now."
"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."
While there are varying opinions about the importance of an overlay, in reality most feel that the decision whether to implement an overlay will vary from carrier to carrier. "Carries have yet to decide how video is done," Rashid said in conjunction with his overlay comments.
PON and broadband equipment provider AFC feels the same way. "We're all looking at all of the possibilities," said Timothy Flood, senior director of product line management at AFC.
Rolling it out
To date, only two companies -- Optical Solutions and Flexlight Networks -- have developed GPON systems for carrier deployment. Outside of that, however, all other BPON manufacturers have yet to rollout GPON equipment, raising questions about whether GPON is ready to replace BPON in real-life deployments.
Things could start changing quickly on the equipment front. Alcatel, AFC, Lucent, Ciena, ECI, and a host of manufacturers are currently looking at ways to upgrade their central-office PON solutions to support GPON operation.
"GPON is just a card swapout," said Gary Bolton, vice president of product marketing in Ciena's Broadband Access Group. "It's an OLT (optical line terminal) blade."
Lucent is planning 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 Technologies Access Networks division. "We're looking heavily toward a GPON implementation."
Chipset vendors are also stepping to help OEMs make GPON come to life. According to Ivancovsky, BroadLight expects to have a GPON chipset available by the end of the first quarter of 2005. Existing BPON chipset players Freescale Semiconductor and Centillium are also working on GPON offerings. Centillium has said that they expect to have a GPON solution in the second half of 2005. Freescale remained mum on a specific timeframe for its chipsets, but did say that chips could hit the market as early as next year 2005.
"We are working on G-PON as a natural outgrowth of PON market demand," said Niket Jindal, business development and marketing manager at Freescale Semiconductor.
The big mystery that remains, however, is when will carriers start implementing GPON. Clearly, existing BPON players, like Verizon, will continue down this path until GPON systems are readily available. Some carriers, such as Bell Canada, have already made the commitment to GPON.
But, there are still a number of carriers that have not yet committed to their PON approach, especially in markets like Europe. If equipment is available and they can wait, most industry members feel that GPON will be a better optional than BPON for these undecided carriers.
"I suspect some carriers will wait for GPON," Infonetics' Howard said.