Glenn Wellbrock’s engineering roots
After four decades shaping optical networking, Glenn Wellbrock has retired. He shares his career highlights, industry insights, and his plans to embrace a quieter life of farming and hands-on projects in rural Kansas.
Glenn Wellbrock’s (pictured) fascination with telecommunications began at an early age. “I didn’t understand how it worked, and I wanted to know,” he recalls.
Wellbrock’s uncle had a small, rural telephone company where he worked while studying, setting the stage for his first full-time job at telecom operator, MCI. Wellbrock entered a world of microwave and satellite systems; MCI was originally named Microwave Communications Incorporated. “They were all ex-military guys, and I’m the rookie coming out of school trying to do my best and learn,” says Wellbrock.
The challenge that dominated the first decade of this century.
The arrival of fibre optics in the late 1980s marked a pivotal shift. As colleagues hesitated to embrace the new “glass” technology, Wellbrock seized the opportunity. “I became the fibre guy,” he says. “My boss said, ‘Anything breaks over there, it’s your problem. You go fix it.’”
This hands-on role propelled him into the early days of optical networking, where he worked on asynchronous systems with bit rates ranging from hundreds of kilobits to over a megabit, before SONET/SDH standards took over.
By the 1990s, with a young family, Wellbrock moved to Texas, contributing to MCI’s development of OC-48 (2.5 gigabit-per-second or Gbps) systems, a precursor to the high-capacity networks that would define his career.
Hitting a speed wall
One of Wellbrock’s proudest achievements was overcoming the barrier to get to speeds faster than 10Gbps, a challenge that dominated the first decade of this century.
Polarisation mode dispersion (PMD) in an optical fibre was a significant hurdle, limiting the distance and reliability of high-speed links. By then, he was working at a start-up and did not doubt that using phase modulation was the answer.
Wellbrock recalls conversations he had with venture capitalists at the time: “I said: ‘Okay, I get we are a company of 40 guys and I don’t even know if they can build it, but somebody’s going to do it, and they’re going to own this place.’”
Wellbrock admits he didn’t know the answer would be coherent optics, but he knew intensity modulation direct detection had reached its limits.
For a short period, Wellbrock was part of Marconi before joining Verizon in 2006. In 2007, he was involved in a Verizon field trial between Miami and Tampa, 300 miles apart, which demonstrated a 100Gbps direct-detection system. “It was so manual,” he admits. “It took three of us working through the night to keep it working so we could show it to the executives in the morning.”
While the trial passed video, it was clear that direct detection wouldn’t scale. The solution lay in coherent detection, which Wellbrock’s team, working with Nortel (acquired by Ciena), finally brought to market by 2009.
“Coherent was like seeing a door,” he says. “PMD was killing you, but you open the door, and it’s a vast room. We had breathing room for almost two decades.”
Verizon’s lab in Texas had multiple strands of production fibre that looped back to the lab every 80km. “We could use real-world glass with all the impairments, but keep equipment in one location,” says Wellbrock.
This setup enabled rigorous testing and led to numerous post-deadline papers at OFC, cementing Verizon’s reputation for optical networking innovation.
Rise of the hyperscalers
Wellbrock’s career spanned a transformative era in telecom, from telco-driven innovation to the rise of hyperscalers like Google and Microsoft.
He acknowledges the hyperscalers’ influence as inevitable due to their scale. “If you buy a million devices, you’re going to get attention,” he says. “We’re buying 100 of the same thing.”
Hyperscalers’ massive orders for pluggable modules and tunable lasers—technologies telcos like Verizon helped pioneer—have driven costs down, benefiting the industry.
However, Wellbrock notes that telcos remain vital for universal connectivity. “Every person, every device is connected,” he says. “Telcos aren’t going anywhere.”
Reliability remains a core challenge, particularly as networks grow. Wellbrock emphasises dual homing—redundant network paths—as telecom’s time-tested solution. “You can’t have zero failures,” he says. “Everything’s got a failure rate associated with it.”
He sees hyperscalers grappling with similar issues, as evidenced by a Google keynote at the Executive Forum at OFC 2025, which sought solutions for network failures linking thousands of AI accelerators in a data centre.
Wellbrock’s approach to such challenges is rooted in collaboration. “You’ve got to work with the ecosystem,” he insists. “Nobody solves every problem alone.”
Hollow-core fibre
Looking forward, what excites Wellbrock is hollow-core fibre, which he believes could be as transformative as SONET, optical amplifiers, and coherent detection.
Unlike traditional fibre, hollow-core fibre uses air-filled waveguides, offering near-zero loss, low latency, and vast bandwidth potential. “If we could get hollow-core fibre with near-zero loss and as much bandwidth as you needed, it would give us another ride at 20 years’ worth of growth,” he says. “It’s like opening another door.”
While companies like Microsoft are experimenting with hollow-core fibre, Wellbrock cautions that widespread adoption is years away. “They’re probably putting in [a high fibre glass] 864 [strand]-count standard glass and a few hollow core [strands],” he notes.
For long-haul routes, the technology promises lower latency and freedom from nonlinear effects, but challenges remain in developing compatible transmitters, receivers, and amplifiers. “All we’ve got to do is build those,” he says, laughing, acknowledging the complexity.
Wellbrock also highlights fibre sensing as a practical innovation, enabling real-time detection of cable damage. “If we can detect an excavator getting closer, we can stop it before it breaks a fibre link,” he explains. This technology, developed in collaboration with partners like NEC and Ciena, integrates optical time-domain reflectometry (OTDR) into transmission systems, thereby enhancing network reliability.
Learnings
Wellbrock’s approach to innovation centres on clearly defining problems to engage the broader ecosystem. “Defining the problem is two-thirds of solving it,” he says, crediting a Verizon colleague, Tiejun J. Xia, for the insight. “If you articulate it well, lots of smart people can help you fix it.”
This philosophy drove his success at OFC, where he used the conference to share challenges, such as fibre sensing, and rally vendor support. “You’ve got to explain the value of solving it,” he adds. “Then you’ll get 10 companies and 1,000 engineers working on it.”
He advises against preconceived solutions or excluding potential partners. “Never say never,” he says. “Be open to ideas and work with anybody willing to address the problem.”
This collaborative mindset, paired with a willingness to explore multiple solutions, defined his work with Xia, a PhD associate fellow at Verizon. “Our favourite Friday afternoon was picking the next thing to explore,” he recalls. “We’d write down 10 possible things and pull on the string that had legs.”
Fibre to Farming
As Wellbrock steps into retirement, he is teaming up with his brother.
The two own 400 acres in Kansas, where wheat farming, hunting, and fishing will define their days. “I won’t miss 100 emails a day or meetings all day long,” he admits. “But I’ll miss the interaction and building stuff.”
Farming offers a chance to work with one’s hands, doing welding and creating things from metal. “I love to build things,” he says. “It’s fun to go, ‘Why hasn’t somebody built this before?’
Farming projects can be completed in a day or over a weekend. “Networks take a long time to build,” he notes. “I’m looking forward to starting a project and finishing it quickly.”
He plans to cultivate half their land to fund their hobbies, using “old equipment” that requires hands-on maintenance—a nod to his engineering roots.
OFC farewell
Wellbrock retired just before the OFC show in March 2025. His attendance was less about work and more about transition, where he spent the conference introducing his successor to vendors and industry peers, ensuring a smooth handoff.
“I didn’t work as hard as I normally do at OFC,” he says. “It’s about meeting with vendors, doing a proper handoff, and saying goodbye to folks, especially international ones.” He also took part in this year’s OFC Rump Session.
Wellbrock admits to some sadness. Yet, he remains optimistic about his future, with plans to possibly return to OFC as a visitor. “Maybe I’ll come just to visit with people,” he muses.
Timeline
- 1984: MCI
- 1987: Started working on fibre
- 2000: Joined start-ups and, for a short period, was part of Marconi
- 2004: Joined Worldcom, which had bought MCI
- 2006: Joined Verizon
- 2025: Retired from Verizon
A tribute
Prof. Andrew Lord, Senior Manager, optical and quantum research, BT
I have had the privilege of knowing Glenn since the 1990s, when BT had a temporary alliance with MCI. We shared a vendor trip to Japan, where I first learnt of his appetite for breakfasting at McDonald’s!
Glenn has been a pivotal figure in our industry since then. A highlight would be the series of ambitious Requests For Information (RFIs) issued by Verizon, which would send vendor account managers scurrying to their R&D departments for cover.
Another highlight would be the annual world-breaking Post-Deadline Paper results at OFC: those thrilling sessions won’t be the same without a Wellbrock paper and neither will the OFC rump sessions, which have benefited from his often brutal pragmatism, always delivered with grace (which somehow made it even worse when defeating me in an argument!).
But it’s grace that defines the man who always has time for people and is always generous enough to share his views and experiences. Glenn will be sorely missed, but he deserves a fulfilling and happy retirement.
Verizon, Ciena and Juniper trial 400 Gigabit Ethernet
Verizon has sent a 400 Gigabit Ethernet signal over its network, carried using a 400-gigabit optical wavelength.
The trial’s goal was to demonstrate multi-vendor interoperability and in particular the interoperability of standardised 400 Gigabit Ethernet (GbE) client signals.
Glenn Wellbrock“[400GbE] Interoperability with the client side has been the long pole in the tent - and continues to be,” says Glenn Wellbrock, director, optical transport network - architecture, design and planning at Verizon. “This was trial equipment, not generally-available equipment.”
It is only the emergence of standardised modules - in this case, an IEEE 400GbE client-side interface specification - that allows multi-vendor interoperability, he says.
By trialing a 400-gigabit lightpath, Verizon also demonstrated the working of a dense wavelength-division multiplexing (DWDM) flexible grid, and a baud rate nearly double the 32-35Gbaud in wide use for 100-gigabit and 200-gigabit wavelengths.
“It shows we can take advantage of the entire system; we don’t have to stick to 50GHz channel spacing anymore,” says Wellbrock.
[400GbE] Interoperability with the client side has been the long pole in the tent - and continues to be
Trial set-up
The trial used Juniper Networks’ PTX5000 packet transport router and Ciena’s 6500 packet-optical platform, equipment already deployed in Verizon’s network.
The Verizon demonstration was not testing optical transmission reach. Indeed the equipment was located in two buildings in Richardson, within the Dallas area. Testing the reach of 400-gigabit wavelengths will come in future trials, says Wellbrock.
The PTX5000 core router has a traffic capacity of up to 24 terabits and supports 10-gigabit, 40-gigabit and 100-gigabit client-side interfaces as well as 100-gigabit coherent interfaces for IP-over-DWDM applications. The PTX5000 uses a mother card on which sits one or more daughter cards hosting the interfaces, what Juniper calls a flexible PIC concentrator (FPC) and physical interface cards (PICs), respectively.
Juniper created a PIC with a 400GbE CFP8 pluggable module implementing the IEEE’s 10km 400GBASE-LR8 standard.
“For us, it was simply creating a demo 400-gigabit pluggable line card to go into the line card Verizon has already deployed,” says Donyel Jones-Williams, director of product marketing management at Juniper Networks.
Donyel Jones-WilliamsThe CFP8 400GbE interface connected the router to Ciena’s 6500 packet-optical platform.
Ciena also used demonstration hardware developed for 400-gigabit trials. “We expect to develop other hardware for general deployment,” says Helen Xenos, senior director, portfolio marketing at Ciena. “We are looking at smaller form-factor pluggables to carry 400 Gigabit Ethernet.”
400-gigabit deployments and trials
Ciena started shipping its WaveLogic Ai coherent modem that implements 400-gigabit wavelengths in the third quarter of 2017. Since then, the company has announced several 400-gigabit deployments and trials.
Vodafone New Zealand deployed 400 gigabits in its national transport network last September, a world first, claims Ciena. German cable operator, Unitymedia, has also deployed Ciena’s WaveLogic Ai coherent modem to deliver a flexible grid and 400-gigabit wavelengths to support growing content delivered via its data centres. And JISC, which runs the UK’s national research and education network, has deployed the 6500 platform and is using 400-gigabit wavelengths.
Helen Xenos
Last September, AT&T conducted its own 400-gigabit trial with Ciena. With AT&T’s trial, the 400-gigabit signal was generated using a test bed. “An SDN controller was used to provision the circuit and the [400-gigabit] signal traversed an OpenROADM line system,” says Xenos.
Using the WaveLogic Ai coherent modem and its support for a 56Gbaud rate means that tunable capacity can now be doubled across applications, says Xenos. The wavelength capacity used for long-haul distances can now be 200 gigabits instead of 100 gigabits, while metro-regional networks spanning 1,000km can use 300-gigabit wavelengths. Meanwhile, 400-gigabit lightpaths suit distances of several hundred kilometres.
It is the large data centre operators that are driving the majority of 400 gigabit deployments, says Ciena. The reason the 400-gigabit announcements relate to telecom operators is because the data centre players have not gone public with their deployments, says Xenos.
Juniper Networks’ PTX5000 core router with 400GbE interfaces will primarily be used by the telecom operators. “We are in trials with other providers on 400 gigabits,” says Jones-Williams. “Nothing is public as yet.”
Verizon tips silicon photonics as a key systems enabler
Part 3: An operator view
Glenn Wellbrock is upbeat about silicon photonics’ prospects. Challenges remain, he says, but the industry is making progress. “Fundamentally, we believe silicon photonics is a real enabler,” he says. “It is the only way to get to the densities that we want.”
Glenn Wellbrock
Wellbrock adds that indium phosphide-based photonic integrated circuits (PICs) can also achieve such densities.
But there are many potential silicon photonics suppliers because of its relatively low barrier to entry, unlike indium phosphide. "To date, Infinera has been the only real [indium phosphide] PIC company and they build only for their own platform,” says Wellbrock.
That an operator must delve into emerging photonics technologies may at first glance seem surprising. But Verizon needs to understand the issues and performance of such technologies. “If we understand what the component-level capabilities are, we can help drive that with requirements,” says Wellbrock. “We also have a better appreciation for what the system guys can and cannot do.”
Verizon can’t be an expert in the subject, he says, but it can certainly be involved. “To the point where we understand the timelines, the cost points, the value-add and the risk factors,” he says. “There are risk factors that we also want to understand, independent of what the system suppliers might tell us.”
The cost saving is real, but it is also the space savings and power saving that are just as important
All the silicon photonics players must add a laser in one form or another to the silicon substrate since silicon itself cannot lase, but pretty much all the other optical functions can be done on the silicon substrate, says Wellbrock: “The cost saving is real, but it is also the space savings and power saving that are just as important.”
The big achievement of silicon photonics, which Wellbrock describes as a breakthrough, is the getting rid of the gold boxes around the discrete optical components. “How do I get to the point where I don’t have fibre connecting all these discrete components, where the traces are built into the silicon, the modulator is built in, even the detector is built right in.” The resulting design is then easier to package. “Eventually I get to the point where the packaging is glass over the top of that.”
So what has silicon photonics demonstrated that gives Verizon confidence about its prospects?
Wellbrock points to several achievements, the first being Infinera’s PICs. Yes, he says, Infinera’s designs are indium phosphide-based and not silicon photonics, but the company makes really dense, low-power and highly reliable components.
He also cites Cisco’s silicon photonics-based CPAK 100 Gig optical modules, and Acacia, which is applying silicon photonics and its in-house DSP-ASICs to get a lower power consumption than other, high-end line-side transmitters.
Verizon believes the technology will also be used in CFP4 and QSFP28 optical modules, and at the next level of integration that avoids pluggable modules on the equipment's faceplate altogether.
But challenges remain. Scale is one issue that concerns Verizon. What makes silicon chips cheap is the fact that they are made in high volumes. “It [silicon photonics] couldn’t survive on just the 100 gigabit modules that the telecom world are buying,” says Wellbrock.
If these issues are not resolved, then indium phosphide continues to win for a long time because that is where the volumes are today
When Verizon asks the silicon photonics players about how such scale will be achieved, the response it gets is data centre interconnect. “Inside the data centre, the optics is growing so rapidly," says Wellbrock. "We can leverage that in telecom."
The other issue is device packaging, for silicon photonics and for indium phosphide. It is ok making a silicon-photonics die cheaply but unless the packaging costs can be reduced, the overall cost saving is lost. ”How to make it reliable and mainstream so that everyone is using the same packaging to get cost down,” says Wellbrock.
All these issues - volumes, packaging, increasing the number of applications a single part can be applied to - need to be resolved and almost simultaneously. Otherwise, the technology will not realise its full potential and the start-ups will dwindle before the problems are fixed.
“If these issues are not resolved, then indium phosphide continues to win for a long time because that is where the volumes are today,” he says.
Verizon, however, is optimistic. “We are making enough progress here to where it should all pan out,” says Wellbrock.
Verizon readies its metro for next-generation P-OTS
Verizon is preparing its metro network to carry significant amounts of 100 Gigabit traffic and has detailed its next-generation packet-optical transport system (P-OTS) requirements. The operator says technological advances in 100 Gig transmission and new P-OTS platforms - some yet to be announced - will help bring large scale 100 Gig deployments in the metro in the next year or so.
Glenn Wellbrock
The operator says P-OTS will be used for its metro and regional networks for spans of 400-600km. "That is where we have very dense networks," says Glenn Wellbrock, director of optical transport network architecture and design at Verizon. "The amount of 100 Gig is going to be substantially higher than it was in long haul."
Verizon announced in April that it had selected Fujitsu and Coriant for a 100 Gig metro upgrade. The operator has already deployed Fujitsu's FlashWave 9500 and the Coriant 7100 (formerly Tellabs 7100) P-OTS platforms. "The announcement [in April] is to put 100 Gig channels in that embedded base," says Wellbrock.
The operator has 4,000 reconfigurable optical add/ drop multiplexers (ROADMs) across its metro networks worldwide and all support 100 Gig channels. But the networks are not tailored for high-speed transmission and hence the cost of 100 Gig remains high. For example, dispersion compensation fibre, and Erbium-doped fibre amplifiers (EDFA) rather than hybrid EDFA-Raman are used for the existing links. "It [the network] is not optimised for 100 Gig but will support it, and we are using [100 Gig] on an as-needed basis," says Wellbrock.
The metro platform will be similar to those used for Verizon's 100 Gig long-haul in that it will be coherent-based and use advanced, colourless, directionless, contentionless and flexible-grid ROADMs. "But all in a package that fits in the metro, with a much lower cost, better density and not such a long reach," says Wellbrock.
The amount of 100 Gig is going to be substantially higher than it was in long haul
One development that will reduce system cost is the advent of the CFP2-based line-side optical module; another is the emergence of third- or fourth-generation coherent DSP-ASICs. "We are getting to the point where we feel it is ready for the metro," says Wellbrock. "Can we get it to be cost-competitive? We feel that a lot of the platforms are coming along."
The latest P-OTS platforms feature enhanced packet capabilities, supporting carrier Ethernet, multi-protocol label switching - transport profile (MPLS-TP), and high-capacity packet and Optical Transport Network (OTN) switching. Recently announced P-OTS platforms suited to Verizon's metro request-for-proposal include Cisco Systems' Network Convergence System (NCS) 4000 and Coriant's mTera. Verizon says it expects other vendors to introduce platforms in the next year.
Verizon still has over 250,000 SONET elements in its network. Many are small and reside in the access network but SONET also exists in its metro and regional networks. The operator is keen to replace the legacy technology but with such a huge number of installed network elements, this will not happen overnight.
Verizon's strategy is to terminate the aggregated SONET traffic at its edge central offices so that it only has to deal with large Ethernet and OTN flows at the network node. "We plan to terminate the SONET, peel out the packets and send them in a packet-optimised fashion," says Wellbrock. In effect, SONET is to be stopped from an infrastructure point of view, he says, by converting the traffic for transport over OTN and Ethernet.
SDN and multi-layer optimisation
The P-OTS platform, with its integrated functionality spanning layer-0 to layer-2, will have a role in multi-layer optimisation. The goal of multi-layer optimisation is to transport services on the most suitable networking layer, typically the lowest, most economical layer possible. Software-defined networking (SDN) will be used to oversee such multi-layer optimisation.
However, P-OTS, unlike servers used in the data centre, are specialist rather than generic platforms. "Optical stuff is not generic hardware," says Wellbrock. Each P-OTS platform is vendor-proprietary. What can be done, he says, is to use 'domain controllers'. Each vendor's platform will have its own domain controller, above which will sit the SDN controller. Using this arrangement, the vendor's own portion of the network can be operated generically by an SDN controller, while benefitting from the particular attributes of each vendor's platform using the domain controller.
There is always frustration; we always want to move faster than things are coming about
Verizon's view is that there will be a hierarchy of domain and SDN controllers."We assume there are going to be multiple layers of abstraction for SDN," says Wellbrock. There will be no one, overriding controller with knowledge of all the networking layers: from layer-0 to layer-3. Even layer-0 - the optical layer - has become dynamic with the addition of colourless, directionless, contentionless and flexible-grid ROADM features, says Wellbrock.
Instead, as part of these abstraction layers, there will be one domain that will control all the transport, and another that is all-IP. Some software element above these controllers will then inform the optical and IP domains how best to implement service tasks such as interconnecting two data centres, for example. The transport controller will then inform each layer its particular task. "Now I want layer-0 to do that, and that is my Ciena box; I need layer-1 to do this and that happens to be a Cyan box; and we need MPLS transport to do this, and that could be Juniper," says Wellbrock, pointing out that in this example, three vendor-domains are involved, each with its own domain controller.
Is Verizon happy with the SDN progress being made by the P-OTS vendors?
"There is always frustration; we always want to move faster than things are coming about," says Wellbrock. "The issue, though, is that there is nothing I see that is a showstopper."
Verizon on 100G+ optical transmission developments
Source: Gazettabyte
Feature: 100 Gig and Beyond. Part 1:
Verizon's Glenn Wellbrock discusses 100 Gig deployments and higher speed optical channel developments for long haul and metro.
The number of 100 Gigabit wavelengths deployed in the network has continued to grow in 2013.
According to Ovum, 100 Gigabit has become the wavelength of choice for large wavelength-division multiplexing (WDM) systems, with spending on 100 Gigabit now exceeding 40 Gigabit spending. LightCounting forecasts that 40,000, 100 Gigabit line cards will be shipped this year, 25,000 in the second half of the year alone. Infonetics Research, meanwhile, points out that while 10 Gigabit will remain the highest-volume speed, the most dramatic growth is at 100 Gigabit. By 2016, the majority of spending in long-haul networks will be on 100 Gigabit, it says.
The market research firms' findings align with Verizon's own experience deploying 100 Gigabit. The US operator said in September that it had added 4,800, 100 Gigabit miles of its global IP network during the first half of 2013, to total 21,400 miles in the US network and 5,100 miles in Europe. Verizon expects to deploy another 8,700 miles of 100 Gigabit in the US and 1,400 miles more in Europe by year end.
"We expect to hit the targets; we are getting close," says Glenn Wellbrock, director of optical transport network architecture and design at Verizon.
Verizon says several factors are driving the need for greater network capacity, including its FiOS bundled home communication services, Long Term Evolution (LTE) wireless and video traffic. But what triggered Verizon to upgrade its core network to 100 Gig was converging its IP networks and the resulting growth in traffic. "We didn't do a lot of 40 Gig [deployments] in our core MPLS [Multiprotocol Label Switching] network," says Wellbrock.
The cost of 100 Gigabit was another factor: A 100 Gigabit long-haul channel is now cheaper than ten, 10 Gig channels. There are also operational benefits using 100 Gig such as having fewer wavelengths to manage. "So it is the lower cost-per-bit plus you get all the advantages of having the higher trunk rates," says Wellbrock.
Verizon expects to continue deploying 100 Gigabit. First, it has a large network and much of the deployment will occur in 2014. "Eventually, we hope to get a bit ahead of the curve and have some [capacity] headroom," says Wellbrock.
We could take advantage of 200 Gig or 400 Gig or 500 Gig today
Super-channel trials
Operators, working with optical vendors, are trialling super-channels and advanced modulation schemes such as 16-QAM (quadrature amplitude amplitude). Such trials involve links carrying data in multiples of 100 Gig: 200 Gig, 400 Gig, even a Terabit.
Super-channels are already carrying live traffic. Infinera's DTN-X system delivers 500 Gig super-channels using quadrature phase-shift keying (QPSK) modulation. Orange has a 400 Gigabit super-channel link between Lyon and Paris. The 400 Gig super-channel comprises two carriers, each carrying 200 Gig using 16-QAM, implemented using Alcatel-Lucent's 1830 photonic service switch platform and its photonic service engine (PSE) DSP-ASIC.
"We could take advantage of 200 Gig or 400 Gig or 500 Gig today," says Wellbrock. "As soon as it is cost effective, you can use it because you can put multiple 100 Gig channels on there and multiplex them."
The issue with 16-QAM, however, is its limited reach using existing fibre and line systems - 500-700km - compared to QPSK's 2,500+ km before regeneration. "It [16-QAM] will only work in a handful of applications - 25 percent, something of this nature," says Wellbrock. This is good for a New York to Boston, he says, but not New York to Chicago. "From our end it is pretty simple, it is lowest cost," says Wellbrock. "If we can reduce the cost, we will use it [16-QAM]. However, if the reach requirement cannot be met, the operator will not go to the expense of putting in signal regenerators to use 16-QAM do, he says.
Earlier this year Verizon conducted a trial with Ciena using 16-QAM. The goals were to test 16-QAM alongside live traffic and determine whether the same line card would work at 100 Gig using QPSK and 200 Gig using 16-QAM. "The good thing is you can use the same hardware; it is a firmware setting," says Wellbrock.
We feel that 2015 is when we can justify a new, greenfield network and that 100 Gig or versions of that - 200 Gig or 400 Gig - will be cheap enough to make sense
100 Gig in the metro
Verizon says there is already sufficient traffic pressure in its metro networks to justify 100 Gig deployments. Some of Verizon's bigger metro locations comprise up to 200 reconfigurable optical add/ drop multiplexer (ROADM) nodes. Each node is typically a central office connected to the network via a ROADM, varying from a two-degree to an eight-degree design.
"Not all the 200 nodes would need multiple 100 Gig channels but in the core of the network, there is a significant amount of capacity that needs to be moved around," says Wellbrock. "100 Gig will be used as soon as it is cost-effective."
Unlike long-haul, 100 Gigabit in the metro remains costlier than ten 10 Gig channels. That said, Verizon has deployed metro 100 Gig when absolutely necessary, for example connecting two router locations that need to be connected using 100 Gig. Here Verizon is willing to pay extra for such links.
"By 2015 we are really hoping that the [metro] crossover point will be reached, that 100 Gig will be more cost effective in the metro than ten times 10 [Gig]." Verizon will build a new generation of metro networks based on 100 Gig or 200 Gig or 400 Gig using coherent receivers rather than use existing networks based on conventional 10 Gig links to which 100 Gig is added.
"We feel that 2015 is when we can justify a new, greenfield network and that 100 Gig or versions of that - 200 Gig or 400 Gig - will be cheap enough to make sense."
Data Centres
The build-out of data centres is not a significant factor driving 100 Gig demand. The largest content service providers do use tens of 100 Gigabit wavelengths to link their mega data centres but they typically have their own networks that connect relatively few sites.
"If you have lots of data centres, the traffic itself is more distributed, as are the bandwidth requirements," says Wellbrock.
Verizon has over 220 data centres, most being hosting centres. The data demand between many of the sites is relatively small and is served with 10 Gigabit links. "We are seeing the same thing with most of our customers," says Wellbrock.
Technologies
System vendors continue to develop cheaper line cards to meet the cost-conscious metro requirements. Module developments include smaller 100 Gig 4x5-inch MSA transponders, 100 Gig CFP modules and component developments for line side interfaces that fit within CFP2 and CFP4 modules.
"They are all good," says Wellbrock when asked which of these 100 Gigabit metro technologies are important for the operator. "We would like to get there as soon as possible."
The CFP4 may be available by late 2015 but more likely in 2016, and will reduce significantly the cost of 100 Gig. "We are assuming they are going to be there and basing our timelines on that," he says.
Greater line card port density is another benefit once 100 Gig CFP2 and CFP4 line side modules become available. "Lower power and greater density which is allowing us to get more bandwidth on and off the card." sats Wellbrock.
Existing switch and routers are bandwidth-constrained: they have more traffic capability that the faceplate can provide. "The CFPs, the way they are today, you can only get four on a card, and a lot of the cards will support twice that much capacity," says Wellbrock.
With the smaller form factor CFP2 and CFP4, 1.2 and 1.6 Terabits card will become possible from 2015. Another possible development is a 400 Gigabit CFP which would achieve a similar overall capacity gains.
Coherent, not just greater capacity
Verizon is looking for greater system integration and continues to encourage industry commonality in optical component building blocks to drive down cost and promote scale.
Indeed Verizon believes that industry developments such as MSAs and standards are working well. Wellbrock prefers standardisation to custom designs like 100 Gigabit direct detection modules or company-specific optical module designs.
Wellbrock stresses the importance of coherent receiver technology not only in enabling higher capacity links but also a dynamic optical layer. The coherent receiver adds value when it comes to colourless, directionless, contentionless (CDC) and flexible grid ROADMs.
"If you are going to have a very cost-effective 100 Gigabit because the ecosystem is working towards similar solutions, then you can say: 'Why don't I add in this agile photonic layer?' and then I can really start to do some next-generation networking things." This is only possible, says Wellbrock, because of the tunabie filter offered by a coherent receiver, unlike direct detection technology with its fixed-filter design.
"Today, if you want to move from one channel to the next - wavelength 1 to wavelength 2 - you have to physically move the patch cord to another filter," says Wellbrock. "Now, the [coherent] receiver can simply tune the local oscillator to channel 2; the transmitter is full-band tunable, and now the receiver is full-band tunable as well." This tunability can be enabled remotely rather than requiring an on-site engineer.
Such wavelength agility promises greater network optimisation.
"How do we perhaps change some of our sparing policy? How do we change some of our restoration policies so that we can take advantage of that agile photonics later," says Wellbroack. "That is something that is only becoming available because of the coherent 100 Gigabit receivers."
Part 2, click here
Verizon plans coherent-optimised routes
"Next-gen lines will be coherent only"
Glenn Wellbrock, Verizon Business
Muxponders at 40Gbps
Given the expense of OC-768 very short reach transponders, Verizon is a keen proponent of 4x10Gbps muxponders. Instead of using the OC-768 client side interface, Verizon uses 4x10Gbps pluggables which are multiplexed into the 40Gbps line-side interface. The muxponder approach is even more attractive with compared to 40Gbps IP core router interfaces which are considerable more expensive than 4x10Gbps pluggables.
DQPSK will be deployed this year
Verizon has been selective in its use of differential phase-shift keying (DPSK) based 40Gbps transmission within its network. It must measure the polarisation mode dispersion (PMD) on a proposed 40Gbps route and its variable nature means that impairment issues can arise over time. For this reason Verizon favours differential quadrature phase-shift keying (DQPSK) modulation.
According to Wellbrock, DPSK has a typical PMD tolerance of 4 ps while DQPSK is closer to 8 ps. In contrast, 10Gbps DWDM systems have around 12 ps. “That [8 ps of DQPSK] is the right ballpark figure,” he says, pointing out that a measuring a route's PMD must still be done.
Verizon is testing the technology in its labs and Wellbrock says Verizon will deploy 40Gbps DQPSK technology this year.
Cost of 100Gbps
Verizon Business has already deployed Nortel’s 100Gbps dual- polarization quadrature phase-shift keying (DP-QSPK) coherent system in Europe, connecting Frankfurt and Paris. However, given 100Gbps is at the very early stages of development it will take time to meet the goal of costing 2x 40Gbps.
That said, Verizon expects at least one other system vendor to have a 100Gbps system available for deployment this year. And around mid-2011, at least three 300-pin module makers will likely have products. It will be the advent of 100Gbps modules and the additional 100Gbps systems they will enable that will reduce the price of 100Gbps. This has already happened with 40Gbps line side transponders; with 100Gbps the advent of 300-pin MSAs will happen far much quickly, says Wellbrock.
Next-gen routes coherent only
When Verizon starts deploying its next-generation fibre routes they will be optimised for 100Gbps coherent systems. This means that there will be no dispersion compensation fibre used on the links, depending on the 100Gbps receiver’s electronics to execute the dispersion compensation instead.
The routes will accommodate 40Gbps transmission but only if the systems use coherent detection. Moreover, much care will be needed in how these links are architected since they will need to comply with future higher-speed optical transmission schemes.
Verizon expects to start such routes in 2011 and “certainly” in 2012.