Open ROADM gets deployed as work starts on Release 6.0
AT&T has deployed Open ROADM technology in its network and says all future reconfigurable optical add-drop multiplexer (ROADM) deployments will be based on the standard.
“At this point, it is in a single metro and we are working on a second large metro area,” says John Paggi, assistant vice president member of technical staff, network infrastructure and services at AT&T.
Open ROADM listed as a requirement in RFPs (Request For Proposals) from many other service providers
As shown are the various elements included in the disaggregated Open ROADM MSA. Also shown is the hierarchical SDN controller architecture with the federated controllers overseeing the optical layer and the multi-layer controller overseeing the path creation across the layer, from IP to optical. Source: Open ROADM MSA
Meanwhile, the Open ROADM multi-source agreement (MSA) continues to progress, with members working on Release 6.0 of the standard.
Motivation
AT&T is a founding member of the Open ROADM MSA along with system vendors Ciena, Fujitsu and Nokia. The organisation has since grown to 23 members, 13 of which operate networks. Besides AT&T, the communications service providers include Deutsche Telekom, Orange, KDDI, SK Telecom and Telecom Italia.
The initiative was created to promote a disaggregated ROADM standard that enables interoperability between vendors’ ROADMs.
The specification work includes the development of open interfaces to control the ROADMs using software-defined networking (SDN) technology. The scope of the disaggregated design has also been expanded beyond ROADMs to include optical transceivers, OTN switching to handle sub-wavelength traffic, and optical amplifiers.
AT&T viewed the MSA as a way to change the traditional model of assigning two ROADM system vendors for each of its metro regions.
“We had two suppliers to keep each other honest,” says Paggi. “But once we had committed a region to a supplier, we were more or less beholden to that supplier for additional ROADM and transponder purchases.”
AT&T wanted ‘true hyper-competition’ among ROADM and transponder suppliers and the Open ROADM MSA was the result.
The operator saw the MSA as a way to reduce costs and speed up innovation by using an open networking model. Opening up and standardising the design would also allow innovative start-up vendors to participate. With the traditional supply model, an operator would favour larger firms knowing it would be dependent on the suppliers for 5-10 years.
“Because you can mix and match different suppliers, Open ROADM allows us to introduce disrupters to our environment,” says Paggi.
Evolution
The first Open ROADM revision used 100-gigabit wavelengths and a 50GHz fixed grid. A flexible grid and in-line amplification that extended the reach of 100-gigabit wavelengths to 1,000km were then added with Revision 2.
“In Revision 3 we made Open ROADM applicable to more use cases,” says Martin Birk, director member of technical staff, network infrastructure and services, AT&T. “We started introducing things like OTUCn and FlexO in preparation for 400 gigabits.” The OTN ‘Beyond 100 gigabit’ OTUCn format comprises ‘n’ multiples of 100-gigabit OTUC frames, while FlexO refers to the Flexible OTN format.
Adopting OTN technologies is part of enabling Open ROADM to support 200-, 300- and 400-gigabit wavelengths.
Revision 4 then added ODUFlex, 400-gigabit clients, and support for low-noise amplifiers to further extend reach, while the latest fifth revision adds streaming telemetry for network monitoring using work from the OpenConfig industry group.
“A lot of features that widen considerably the application of Open ROADM,” says Birk.
Revision 6.0
The frequency of each Open ROADM release was initially once a year but now the scope of each revision has been curtailed to enable two releases a year. Members are polled as to what new features are required at the start of each standardisation process.
Now, the MSA members are working on revision 6.0 that covers ‘all directions’ of the standard.
“We are improving the control plane interoperability with more features,” says Birk. “Right now you have a single network view; in future, you could have an idealised network plan and a network view with actual failures, and you could provision services across these network views.”
And with the advent of 600-gigabit, 800-gigabit and even 1.2-terabit coherent wavelengths, OpenROADM members may add support for faster speeds than 400 gigabits.
“Just as our suppliers continue to evolve their roadmaps, so does the Open ROADM MSA to stay relevant,” says Birk.
AT&T’s Open ROADM deployments support 100-gigabit wavelengths while the 400-gigabit technology is still in development.
“The ROADMs will not change; the only thing that will change is the software,” says Birk. “And in a disaggregated design, you can leave the ROADMs on version 2.0 and upgrade the transponders to 400 gigabits and version 5.0.”
This, says Birk, is why it is much easier to introduce new technology with an open design compared to monolithic platforms where an upgrade involves all the element management systems, ROADMs and transponders.
Status
The Open ROADM MSA says it is up to individual network operator members to declare the status of their Open ROADM network deployments. Accordingly, the status of overall Open ROADM deployments is unclear.
What AT&T will say is that it is being approached by vendors that want to demonstrate their Open ROADM technology to the operator.
“When we ask them why they have done this without any agreement that AT&T would purchase their solutions, they respond that they are seeing Open ROADM listed as a requirement in RFPs (Request For Proposals) from many other service providers,” says Paggi. “They have taken it upon themselves to develop Open ROADM-compliant products.”
At the OFC show earlier this year, an Open ROADM MSA showcased an SDN controller turning up a wavelength to send virtual machines between two data centres. The SDN controller then terminated the optical connection on completion of the transfer.
Operators AT&T and Orange were part of the demonstration as was the University of Texas, Dallas. “They [the University of Texas] are a supercomputing centre and they can create some nice applications on top of Open ROADM,” says Birk.
The system vendors involved in the OFC demonstration included Ciena, Fujitsu, ECI Telecom, Infinera and Juniper Networks.
PMC advances OTN with 400 Gigabit processor
Optical modules for the line-side are moving beyond 100 Gigabits to 200 Gigabit and now 400 Gigabit transmission rates. Such designs are possible thanks to compact photonics designs and coherent DSP-ASICs implemented using advanced CMOS processes.
An example switching application showing different configurations of the DIGi-G4 OTN processor on the line cards. Source: PMC
For engineers, the advent of higher-speed line-side interfaces sets new challenges when designing the line cards for optical networking equipment. In particular, the framer silicon that interfaces to the coherent DSP-ASIC, on the far side of the optics, must cope with a doubling and quadrupling of traffic.
Such line cards for metro network platforms is where PMC-Sierra is targeting its latest 400 Gigabit DIGI-G4 Optical Transport Network (OTN) processor.
The OTN standard, defined by the telecom standards body of the International Telecommunication Union (ITU-T), performs several roles in the network. It is a layer-one technology that packages packet and circuit-switched traffic. OTN wraps traffic in a variety of container sizes for transport, from 1 Gigabit (OTU1) to 100 Gigabit (OTU4). And now 100 Gigabit can be viewed as a sub-frame, multiples of which can be combined to create even larger frames, dubbed OTUCn, where n is a multiple of 100 Gig.
Using OTN, container traffic can be broken up, switched and recombined within new containers before being transmitted optically. OTN also provides forward error correction and network management features.
PMC’s DIGI-G4 OTN processor is aimed at next-generation packet-optical transport systems (P-OTS) adopting 400 Gig line cards, and for platforms for the burgeoning data centre interconnect market.
“The amounts of traffic internet content providers need between their data centres is astonishing; they are talking hundreds of terabits of traffic,” says Hamish Dobson, director of strategic marketing at PMC. Hyper-scale data centre operators, unlike telcos, do not require OTN switching but they are keen on OTN as the DWDM management layer, he says: “I’m not aware of any of the hyper-scale players who are deploying their own networks who are not using OTN as the un-channelised digital wrapper on their systems.”
The DIGI-G4 does more than simply quadruple OTN traffic throughput compared to PMC’s existing DIGI 120G OTN processor. The chip also adds encryption hardware to secure links while supporting the emerging Transport Software-Defined Networking (Transport SDN).
DIGI-G4
The DIGI-G4 increases by fourfold the traffic throughput while halving the power-per-port compared to PMC's DIGI 120G. System designers must control the total power consumption of the line card, given the greater interface density, and when metro equipment platforms’ power profile is already at 500W-per-slot, says Dobson. PMC has halved the power consumption-per-port by implementing the latest OTN processor in a 28 nm CMOS process and by using more power-efficient serialisers/ deserialisers (serdes).
Internet content providers with their use of distributed data centres is one reason for the device’s introduction of the Advanced Encryption Standard (AES-256). Another is the emergence of cloud services and the need to secure individual customer’s traffic.
“We have added a channelised hardware [encryption] engine,” says Dobson. “The encryption engine is capable of being applied to any OTN channel in the device.”
Other features of the Digi-G4 include input/ output (I/O) capable of 28 Gigabit-per-second (Gbps). This enables the DIGI-G4 to connect directly to CFP2 and CFP4 pluggable optics without the need for gearbox devices on the line card, reducing power and overall cost.
The OTN chip is a hybrid design capable of processing 400 Gigabit of packet traffic or 400 Gig of circuit (time-division multiplexed) traffic, or any combination of the two, with a granularity of one gigabit channels. “It can switch a full 400 Gig's worth of one Gigabit ODU0 channels,” says Dobson.
The Digi-G4 also support a pre-standard implementation of the OTUC2 and OTUC4 transport units that are two and four multiples of 100 Gigabit, respectively. The OTUCn standard is not expected to be ratified before 2017.
We will see the capabilities of these new packet-optical systems coming together with SDN to enable interesting things to be done in the metro
Hamish Dobson
Transport SDN
SDN will have a significant effect on the transport network, says Dobson. In particular Transport SDN where SDN is applied to the transport layers of the wide area network (WAN). As such, OTN plays an important role in multi-layer optimisation. Packet-optical transport systems, which support packet and optical within the same platform, are ideal for getting much more efficiency out of the optical spectrum, he says.
Using Transport SDN to co-ordinate packet, OTN and the optical layer, routing decisions can be made aware of available capacity in the optical domain. In turn, network protection decisions can also be based on optical capacity availability. “The DIGI-G4, being a hybrid processor to enable these multi-layer platforms, is an important element to bring this all together,” says Dobson.
OTN also aids the virtualisation of optical resources whereby individual enterprises can be given a simpler, subset view of the network. “We need more than just wavelength granularity in the network,” says Dobson. Since 100 Gigabit and, in future, 200 and 400 Gig lightwaves, are such large pipes, these are inevitably filled with multiple traffic flows. “Channelised OTN and OTN switching are how carriers are going to break down these massive amounts of optical capacity and partition them for various uses,” says Dobson.
A third element whereby OTN aids Transport SDN is the move to on-demand provisioning by adapting capacity at the OTN layer. Dobson cites the ITU-T G.7044/Y.1347 (G.HAO) standard, which the DIGI-G4 supports, whereby frame size can be adjusted using ODUflex without impacting existing network traffic.
“We will see the capabilities of these new packet-optical systems coming together with SDN to enable interesting things to be done in the metro,” says Dobson.
Samples of the DIGI-G4 are already with customers.
Further reading
White Paper: Benefits of OTN in Transport SDN, click here and then 'documentation'
