VIAVI, a test equipment OEM, held a webinar recently to discuss the state of Ethernet speeds, and the impact of 400G on Pulse Amplitude Modulation 4-level (PAM4), forward error correction; module management; and power and cooling. The webinar, which was presented by Paul Brooks, VIAVI Product Manager, High-Speed Optical Transport, emphasized that turning on 400G Ethernet Hardware requires a new approach in terms of testing.
400G requires powerful module management, according to Brooks. This allows the power of the optical modules to be harnessed and integrated closer with the network elements. “This complexity also means taking more care of the firmware and the data link to the module,” Brooks said.
Although newer than 100G, 400G is well established and is deployed in hyperscale data centers, as well as at telcos and enterprises. 400G is considered the next generation of cloud infrastructure, according to Brooks, offering a fourfold increase in maximum data transfer speed over 100G.
The speed increase to 400 Gbps demanded the change to PAM4, which is a multilevel signal modulation format, for signaling. This doubled the number of bits that can be transmitted in a period of time. “This increase in data speed can cause more issues of errors on the link,” Brooks said. “That means we have to start using a thing called forward error correction code.”
With 400G, the technology has gone from four lanes, electrically, (four for transmit/four for receive) up to eight transmit and eight receive. “We had to double the number of physical lanes going into the module. So we went to a new form factor with double density and that went from four electrical lanes to eight lanes,” Brooks said.
100G pluggable optics require below 3 Watts of power in most cases, but 400G modules require 10 Watts of power and above, some even higher than that. “400G puts a great demand on the design of the power supply circuitry to the module in a network element, and, of course, the overall cooling both at the module level and the system level,” Brooks said.
By J. Sharpe Smith, Inside Towers Technology Editor
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