Spring 2018 Optical Connections Magazine


Lumentum’s Truflex TWIN 1 x 20 WSS ROADM

2020 organisation. In the case of OLS,

to grow smoothly to high port count networks,” he suggests. According to Infinera, there has been a somewhat piecemeal market adoption of the new ROADM capabilities. “Acceptance of CD architecture is, I think, much further along than the embrace of CDC,” says Gill. “The reason for that is that CDC, in the way that some vendors introduce it, does actually increase costs not significantly.” According to Gill, to deliver the Contentionless characteristic, most vendors’ solutions use fibre-switched muxes. These have active optical components designed to allow a fibre with some wavelengths on it to be plugged into one port, and have those wavelengths appear at any other port on the device without having to worry about what’s going on with other wavelengths in other ports. He likens it to an Ethernet switch with full VLAN separation between all the ports in a system. “It’s kind of a separation that’s pretty easy to do in the electronic domain for Ethernet switches, but it’s somewhat expensive to do in the optical domain with these fibre-switched muxes,” he maintains. “That’s been a sticking point.” But Gill is upbeat about the Flex-grid future: “I think the ‘F’ part of it is not just going to be an optional improvement or optimisation – which is kind of how it started out – but in the very near future it Flex-grid becomes necessary because transponder technology is moving to higher baud rates (signalling rates) that don’t work in the 50 GHz fixed grid systems. Nor has the adoption of the varieties of new generation ROADMs been uniform across dierent geographic markets. The USA and Europe have been in the vanguard of initiatives, while China has been late to the party, although deployments in that market are now picking up. will be a mandatory requirement.” The reasoning here is that going implementations could be majorly influenced by the concept of Open Optical Networking in general, and of Open Line Systems (OLS) in particular. One simplified vision for an Open Optical Network might be that it is one in which various components are realised in disaggregated, standardised non- proprietary forms that can be assembled in an optimised mixed-and-matched fashion. This could encompass open source software, including Software- Defined Network management, open APIs and open hardware. Organisations and initiatives backing open optical hardware include the Open ROADM Multi-Source Agreement, the Telecom Infra Project, the Open Networking Foundation and the Optical Network OPENMINDED Future ROADM design and

the focus is on disaggregating WDM transport system elements, such as ROADMs, optical amplifiers, transponders and terminals,

such that new network builders and operators could put together interoperable, best-in-class functional transport network blocks sourced from dierent vendors. Some aspects of interoperability may be more beneficial than others. For example Infinera, which is a participant in the Open ROADM MSA and the TIP, believes that, due to the rapid pace of innovation by particular vendors in this sector, it isn’t yet useful or practical to talk of hooking up transponders from dierent vendors. Infinera sees the largest near-term benefit in decoupling the transponders and the OLS, so transponders from one vendor operate seamlessly over another vendor’s OLS. In this context, the potential attractions of openness include the lessening of vendor lock-in, lower CapEx and OpEx, increased operational flexibility, and higher levels of service and product innovation. But not everyone is backing the notion of Open Optical Networks. In findings released in January from IHS Markit’s latest Optical Network Strategies Service Provider Survey (analyst Heidi Adams Senior Research Director, Transport Networks), service providers appear to diverge on optical disaggregation. Highlights of this survey included: ● In a December 2017 IHS Markit survey of service providers using optical in the use of disaggregated optical equipment in their networks, up from 33% in 2016. ● Among the service providers planning to introduce disaggregated optical systems, 44% plan to implement these systems by the end of 2018, rising to 69% by the end of 2019. ● However, 27% of respondents indicated that they would not be pursuing disaggregation, up from 17% in 2016. OLS? Bringing about the necessary changes in test methodologies and operational procedures might be discouraging some network operators. Others might consider the idea of full blown SDN daunting. There may be issues with the required integration overhead, and with the potential lack of transmission and switching equipment, 47%t of respondents indicated interest What might be discouraging the adoption of Open Optical Networks and

interoperability and reliability. As remarked by Gill, introducing multiple vendors and changing the way networks are built always requires investment on the part of the operators. “Some don’t see the potential savings or the leverage they have over vendors as being worth it,” ventures Gill. These, he concludes, will probably wait and see how the open proposition pans out, and if it does well, join in later.

Software-Defined Network control and management capabilities are central to the concept of Open Optical Networks and to the operation of new generation ROADMs. “SDN and CDC-F go hand-in- hand. SDN solutions are part of the equation when you talk about where ROADMs are going,” says Infinera’s Gill. “If you tried to apply SDN to an older fixed optical add-drop multiplexer you wouldn’t do anything.” So what does SDN deliver to today’s ROADMs? Quite a lot it seems. “With SDN you can control the ROADM in terms of SOFTLY DOES IT

end-to-end connectivity management and virtualised

protection and restoration management, and it can also be used for bandwidth management,” adds Uwe Fischer, Coriant Executive Vice President, R&D and PLM, and CTO.


| ISSUE 12 | Q1 2018


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