Gazettabyte spoke with BT, Level 3 Communications and Verizon about their 100 Gigabit optical transmission plans and the challenges they see regarding the technology.
Briefing: 100 Gigabit
Part 1: Operators
Operators will use 100 Gigabit-per-second (Gbps) coherent technology for their next-generation core networks. For metro, operators favour coherent and have differing views regarding the alternative, 100Gbps direct-detection schemes. All the operators agree that the 100Gbps interfaces - line-side and client-side - must become cheaper before 100Gbps technology is more widely deployed.
"It is clear that you absolutely need 100 Gig in large parts of the network"
Steve Gringeri, Verizon
100 Gigabit status
Verizon is already deploying 100Gbps wavelengths in its European and US networks, and will complete its US nationwide 100Gbps backbone in the next two years.
"We are at the stage of building a new-generation network because our current network is quite full," says Steve Gringeri, a principal member of the technical staff at Verizon Business.
The operator first deployed 100Gbps coherent technology in late 2009, linking Paris and Frankfurt. Verizon's focus is on 100Gbps, having deployed a limited amount of 40Gbps technology. "We can also support 40 Gig coherent where it makes sense, based on traffic demands," says Gringeri.
Level 3 Communications and BT, meanwhile, have yet to deploy 100Gbps technology.
"We have not [made any public statements regarding 100 Gig]," says Monisha Merchant, Level 3’s senior director of product management. "We have had trials but nothing formal for our own development." Level 3 started deploying 40Gbps technology in March 2009.
BT expects to deploy new high-speed line rates before the year end. "The first place we are actively pursuing the deployment of initially 40G, but rapidly moving on to 100G, is in the core,” says Steve Hornung, director, transport, timing and synch at BT.
Operators are looking to deploy 100Gbps to meet growing traffic demands.
"If I look at cloud applications, video distribution applications and what we are doing for wireless (Long Term Evolution) - the sum of all the traffic - that is what is putting the strain on the network," says Gringeri.
Verizon is also transitioning its legacy networks onto its core IP-MPLS backbone, requiring the operator to grow its base infrastructure significantly. "When we look at demands there, it is clear that you absolutely need 100 Gig in large parts of the network," says Gringeri.
Level 3 points out its network between any two cities has been running at much greater capacity than 100 Gbps so that demand has been there for years, the issue is the economics of the technology. "Right now, going to 100Gbps is significantly a higher cost than just deploying 10x 10Gbps," says Level 3's Merchant.
BT's core network comprises 106 nodes: 20 in a fully-meshed inner core, surrounded by an outer 86-node core. The core carries the bulk of BT's IP, business and voice traffic.
"We are taking specific steps and have business cases developed to deploy 40G and 100G technology: alternative line cards into the same rack," says Hornung.
Coherent and direct detection
Coherent has become the default optical transmission technology for operators' next-generation core networks.
BT says it is a 'no-brainer' that 400Gbps and 1 Terabit-per-second light paths will eventually be deployed in the network to accommodate growing traffic. "Rather than keep all your options open, we need to make the assumption that technology will essentially be coherent going forward because it will be the bandwidth that drives it," says Hornung.
Beyond BT's 106-node core is a backhaul network that links 1,000 points-of-presence (PoPs). It is this part of the network that BT will consider 40Gbps and perhaps 100Gbps direct-detection technology. "If it [such technology] became commercially available, we would look at the price, the demand and use it, or not, as makes sense," says Hornung. "I would not exclude at this stage looking at any technology that becomes available." Such direct-detection 100Gbps solutions are already being promoted by ADVA Optical Networking and MultiPhy.
However, Verizon believes coherent will also be needed for the metro. "If I look at my metro systems, you have even lower quality amplifiers, and generally worse signal-to-noise," says Gringeri. “Based on the performance required, I have no idea how you are going to implement a solution that isn't coherent."
Even for shorter reach metro systems - 200 or 300km- Verizon believes coherent will be the implementation, including expanding existing deployments that carry 10Gbps light paths and that use dispersion-compensated fibre.
Level 3 says it is not wedded to a technology but rather a cost point. As a result it will assess a technology if it believes it will address the operator's needs and has a cost performance advantage.
100 Gig deployment stages
The cost of 100Gbps technology remains a key challenge impeding wider deployment. This is not surprising since 100Gbps technology is still immature and systems shipping are first-generation designs.
Operators are willing to pay a premium to deploy 100Gbps light paths at network pinch-points as it is cheaper that lighting a new fibre.
Metro deployments of new technology such as 100Gbps occur generally occur once the long-haul network has been upgraded. The technology is by then more mature and better suited to the cost-conscious metro.
Applications that will drive metro 100Gbps include linking data centre and enterprises. But Level 3 expects it will be another five years before enterprises move from requesting 10 Gigabit services to 100 Gigabit ones to meet their telecom needs.
Verizon highlights two 100Gbps priorities: the high-end performance dense WDM systems and client-side 'grey' (non-WDM) optics used to connect equipment across distances as short as 100m with ribbon cable to over 2km or 10km over single-mode fibre.
"I would not exclude at this stage looking at any technology that becomes available"
Steve Hornung, BT
"Grey optics are very costly, especially if I’m going to stitch the network and have routers and other client devices and potential long-haul and metro networks, all of these interconnect optics come into play," says Gringeri.
Verizon is a strong proponent of a new 100Gbps serial interface over 2km or 10km. At present there are the 100 Gigabit interface and the 10x10 MSA. However Gringeri says it will be 2-3 years before such a serial interface becomes available. "Getting the price-performance on the grey optics is my number one priority after the DWDM long haul optics," says Gringeri.
Once 100Gbps client-side interfaces do come down in price, operators' PoPs will be used to link other locations in the metro to carry the higher-capacity services, he says.
The final stage of the rollout of 100Gbps will be single point-to-point connections. This is where grey 100Gbps comes in, says Gringeri, based on 40 or 80km optical interfaces.
Source: Gazettabyte
Tackling costs
Operators are confident regarding the vendors’ cost-reduction roadmaps. "We are talking to our clients about second, third, even fourth generation of coherent," says Gringeri. "There are ways of making extremely significant price reductions."
Gringeri points to further photonic integration and reducing the sampling rate of the coherent receiver ASIC's analogue-to-digital converters. "With the DSP [ASIC], you can look to lower the sampling rate," says Gringeri. "A lot of the systems do 2x sampling and you don't need 2x sampling."
The filtering used for dispersion compensation can also be simpler for shorter-reach spans. "The filter can be shorter - you don't need as many [digital filter] taps," says Gringeri. "There are a lot of optimisations and no one has made them yet."
There are also the move to pluggable CFP modules for the line-side coherent optics and the CFP2 for client-side 100Gbps interfaces. At present the only line-side 100Gbps pluggable is based on direct detection.
"The CFP is a big package," says Gringeri. "That is not the grey optics package we want in the future, we need to go to a much smaller package long term."
For the line-side there is also the issue of the digital signal processor's (DSP) power consumption. "I think you can fit the optics in but I'm very concerned about the power consumption of the DSP - these DSPs are 50 to 80W in many current designs," says Gringeri.
One obvious solution is to move the DSP out of the module and onto the line card. "Even if they can extend the power number of the CFP, it needs to be 15 to 20W," says Gringeri. "There is an awful lot of work to get where you are today to 15 to 20W."
* Monisha Merchant left Level 3 before the article was published.
Further Reading:
100 Gigabit: The coming metro opportunity - a position paper, click here
Click here for Part 2: Next-gen 100 Gig Optics