CESNET Validated Deployment of 400G QSFP-DD Transceivers for High-Speed Transmission Over a Record Distance of 846 Kilometers

Prague, 3 December 2024--The CESNET association has successfully verified the functionality of tunable coherent Cisco QSFP-DD Bright 400G ZR+ transceivers for high-speed data transmission. Tests demonstrated the possibility of connecting two switches at a speed of 400Gbps over a distance of up to 846 kilometers, without using a transponder and with zero error rates. This represents an operational cost savings and enables better response to growing data volumes while allowing for flexible interconnection between data centers.

CESNET3: A New Generation of DWDM Network with 400Gbps Capacity for Flexible Data Center Interconnection

Two years ago, we successfully completed the modernization of the DWDM network with support for flexgrid, omnidirectional, colorless, and contentionless. The new generation CESNET3 network spans over the Czech Republic with four rings and enables the transmission of new types of coherent signals at speeds of 400Gbps. Multiple independent paths ensure high service availability and flexible data center interconnections. Until now, we had used transponders for 400Gbps transmissions, but for the first time, we have verified the functionality of tunable coherent Cisco QSFP-DD Bright 400G ZR+ transceivers, which were not available at the time the network was designed. These transceivers are also equipped with an EDFA amplifier with a transmission power of +1 dBm, making them suitable for integration into the DWDM network alongside existing signals.

Two-Week CESNET3 Test Confirmed the Reliability of 400G Transmission Over 846 km

The testing took place over two weeks on the operational Cisco NCS 2000 DWDM system, using Cisco ASR 9903 routers equipped with QSFP-DD Bright 400G ZR+ transceivers. These transceivers support multiple modulation types, enabling data rates of 100, 200, 300, and 400Gbps. On the test route, we successfully achieved the highest possible speed of 400Gbps with 16QAM modulation, zero PostFEC error rates, and a Q-margin of 0.40 dB. The test route between Prague and Brno spanned a total of 846 kilometers, did not use RAMAN amplifiers, and was deliberately constructed to achieve the longest possible distance, ensuring data center connections even in cases where primary routes are unavailable. For this reason, the route passed through Ústí nad Labem, Liberec, Hradec Králové, Olomouc, and Zlín. The signal traversed a total of 14 DWDM locations in the CESNET3 network, including eight with multi-directional ROADM systems and six with EDFA optical amplifiers. The results confirm the overall high quality of the CESNET3 transmission network.

Statements from Project Leaders

"The verification relates to the modernization of compute and storage capacities, where we anticipate increasing demands for high-volume data transfers and the use of flexible data center interconnections. Equipping the network's active elements (switches and routers) with QSFP-DD Bright 400G ZR+ transceivers also brings lower power consumption, space savings, fewer devices, and consequently lower overall operational costs," said Ing. Jan Růžička, Deputy for E-Infrastructure.

"The CESNET academic network is unique both in Europe and globally. I am delighted that the very first test of our new transceiver in an NREN environment was conducted in collaboration with CESNET colleagues. This allows CESNET to offer higher data transfer speeds to connected universities without the need for complex upgrades to the nationwide network. At the same time, the number of devices in the network does not need to increase, which saves energy and related costs," added Peter Morvay, Systems Architect at Cisco Systems.