The 400G-BIDI Module from Arista is Capable of being Broken out into 4x 100G-BIDI or 4x 100G-SR1.2 Links. What is the Difference Between 100G-BIDI and 100G-SR1.2?

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Answered on 9:02 am

The difference between 100G-BIDI and 100G-SR1.2 is mainly in the number of optical lanes and the modulation solution. 100G-BIDI uses two optical lanes, one for each direction, over a duplex LC multi-mode fiber. 100G-SR1.2 uses four optical lanes, two for each direction, over the same fiber. 100G-BIDI uses NRZ (Non-Return-to-Zero) modulation, which means each bit is encoded as a single symbol. 100G-SR1.2 uses PAM4 (Pulse Amplitude Modulation) modulation, which means each symbol encodes two bits. PAM4 enables higher data rates with lower baud rates, but also introduces more noise and complexity. Both 100G-BIDI and 100G-SR1.2 are compliant to IEEE802.3bm 100GBASE-SR4 standard. The main advantage of 100G-BIDI is that it can reuse the existing 40G-BIDI infrastructure and reduce the fiber cabling cost. The main advantage of 100G-SR1.2 is that it can interoperate with 400G-SR4.2 and provide a future-proof solution for higher bandwidth demand.

Another difference between 100G-BIDI (100G-SRBD) and 100G-SR1.2 is the FEC (Forward Error Correction) used. 100G-BIDI (100G-SRBD) modules have been widely deployed for 100G operation over duplex MMF and use a FEC implementation that was developed prior to the IEEE standardization of KP-FEC for 50G PAM-4 based modules. Because of the differences in FEC implementation, 100G-SRBD and 100G-SR1.2 modules are not interoperable with each other.

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