GARR optical network used to be composed of two separate optical network domains on its national infrastructure. With the aim to integrate these two domains and deliver high performance services all over its infrastructure, we implemented the so called alien wavelength technique, thus improving the overall efficiency of the Italian research and education network in a cost-effective way. This paper describes the activity, results, and our experience in the integration of alien wavelengths in a production environment, with a special emphasis on deployment and operational issues.
In order to match the ever evolving needs and requirements of the Italian research and education community, we recently started an evolution process to update GARR network infrastructure and innovate the services provided. Indeed, in a global scenario characterised by an exponential growth of Internet traffic and a continuous strive for innovative solutions we started a re-definition of both our conventional network design and our common practices in device engineering [1,2].
GARR is the Italian NREN (National Research and Education Network) connecting over 1000 sites all over Italy. Its user community is composed of universities, research institutes, research hospitals, cultural institutes, libraries, museums, and schools.
GARR optical network is based on two geographically separated infrastructures. These infrastructures are based on technologies from different vendors and were deployed about four years apart. The first infrastructure deployed, is operating since 2011 in Northern and Central Italy while the second one, implemented in 2015, is operational in the South. The two infrastructures are very diverse from the technological point of view. The coexistence of such infrastructures led GARR to design an integration solution to transmit signals from the most recent technology over the older one. From the technological point of view, the infrastructure in Northern and Central Italy employs a Huawei OptiX OSN platform. Its nodes include ROADM (Reconfigurable Optical Add and Drop Multiplexer) modules, add/drop boards able to support up to 80 channels in the C-band with a 50GHz grid and OTN (Optical Transport Network) switching matrices. The amplification is performed with EDFA (Erbium-Doped Fibre Amplifier) or Raman amplifiers, and DCMs (Dispersion Compensating Modules) are inserted on the fibre lines in order to correct the chromatic dispersion. This optical network is optimised for Intensity Modulation with Direct Detection (IM-DD) and the channels are mainly 10Gbps with few 40Gbps. Here, client services are from 1GEth up to 10GEth. In Southern Italy, instead, the infrastructure is DCM-free and the transmission of signals is performed with coherent technology. The network is equipped with Infinera DTN-X, a platform able to transmit 500Gbps super-channels. Each of them is built on 10 optical carriers spaced at 200GHz in C-band with a 25GHz grid. Optical channels are grouped in pairs that can be enabled and managed with QPSK (Quadrature Phase Shift Keying) or BPSK (Binary Phase Shift Keying) modulation, thus allowing a flexible use of the available spectrum, and an optimal balance between reach and capacity. Client services on this part of the network range from 10GEth to 100GEth.
Considered this technologically heterogeneous infrastructure, within GARR we studied a viable solution to match the highbandwidth capacity requirements of our user community with the existing network. As optical communications are becoming more and more spectrum efficient thanks to coherent transmissions and digital signal processing, in GARR we thought to exploit the coherent transmission infrastructure of the Southern network and to extend it to the North by means of the so-called alien wavelength (AW) technique [3,4]. Thanks to AWs, it was indeed possible to harmonise and develop GARR infrastructure by extending the 100GEth capacity already present in the Southern part of the network to the whole national infrastructure in an agile and cost-effective method. The AW technique is a hybrid solution based on the transmission and reception of optical signals, called alien wavelengths, generated on an infrastructure, which is different from the transport one. Therefore, the transponder light is sourced from a platform and is transported in the host optical domain regardless of the Dense Wavelength Division Multiplexing (DWDM) equipment vendor. So, the AW concept disaggregates the transponder elements from the optical DWDM system. In the specific case of GARR optical infrastructure, this method made possible the integration of the two separated optical networks in one single domain, able to homogeneously deliver the needed network services.
The integration between the two infrastructures (the one providing the transponders and the one providing the photonic layer) was the key issue that required careful design and operational tuning. For this reason, we conducted a dedicated field trial to test a solution to be then implemented in the production network, following the scheme shown in Fig. 2. Fig. 2. Alien wavelength integration setup 1 Bit Error Rate before Forward Error Correction This designed solution can be summarised in these three main building blocks:
• Alien wavelength domain: The network elements generating and operating AW signals are normally installed at the service end-points. They are mainly composed of transponders mounted for example on white-boxes, DCI (Data Centre Interconnect) or OTN switches.
• Native (host)
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