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== Optical

A critical building block of COSMOS is the optical transport network and its unique ability to emulate optical
front/mid/back-haul (x-haul) networks, which is currently not supported by other testbeds. It is used to enable high bandwidth and low latency networking and to support experimentation with emerging and future wireless technologies and applications. Using WDM with wavelength switching in colorless, reconfigurable optical add-drop multiplexers (ROADMs), COSMOS enables a wide range of x-haul networks with different topologies in a real metropolitan setting. The optical core network and connection to other
testbed components are shown in Fig. 1.

[[Image(Optical.jpg, width=800)]]
[[BR]] Figure 1: core optical switching architecture and the switching architecture

The core of the architecture is based on a Calient S320 320×320 space switch (SS) that is deployed in the Data Center at CU providing a remotely configurable fiber plant. Each fiber supports 96 fully transparent channels, which are flexgrid configurable to provision 10/100 Gbps wavelengths. 20 ROADM units are connected to the central SS via 20×4 add/drop fiber pairs. In addition, 20×16 add/drop pairs connect the ROADM units to top of rack (ToR) switches and servers in the CU CRF data center. The 20 fiber pairs per ROADM can be reconfigured to support various requirements from connected servers through top-layer user
applications orchestrated by an SDN controller. The central SS is directly connected via dark fiber (provided by ZenFi
and NYC) to the colocation site at 32 AoA that also houses the NYU data center.
 
=== Calient Space Switch
The space switch located in the CRF Datacenter is a [https://www.calient.net/products/s-series-photonic-switch/ Calient S320].

=== ROADM
The ROADMs located in the CRF Datacenter (Mudd 4th Floor, Columbia) are [https://www.lumentum.com/en/products/dci-roadm-graybox/ Lumentum ROADM Grayboxes].