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MHz is the frequency or rate at which a wave will cycle per second. 1 Megahertz would be equal to 10^6 Hertz or 1 million cycles per second.

Mbps refers to the how many bits of data is transmitted trough a media (such as fiber optic cable) per second.

MHz and Mbps are not equal, the confusion occurs because MHz works with analogue signals while a data transfer occurs digitally.

Transferring data rate (Mbps) to a cable is dependent upon encoding techniques. “Manchester” encoding is used for Standard Ethernet (10 Mbps), which is a two-level encoding technique that requires a minimum of 10 MHz. Cat3 copper cable offers 16 MHz and is why it was acceptable for Standard Ethernet.

This article examines the options for the modulation formats for serial optical transmission of 100 Gb/s and beyond.

The first part covers classical binary electronic time division multiplexed 100 Gbit/s NRZ systems, operating a highest speed, and mature product solutions of system vendors running at lower symbol rates which are using quaternary phase shift keying and polarization division multiplexing, coherent technologies and digital signal processing in the receiver.

The second part covers the next generation of transmission systems carrying data at channel bitrates higher than 100 Gbit/s, e.g. 400 Gbit/s up to 1 Tbit/s or even beyond, which may apply higher constellation M-QAM modulation of a single carrier or multiple electrical carriers and optical superchannels which also form one WDM channel.

Auto-negotiation is the feature that allows a port on a switch, router, server, or other device to communicate with the device on the other end of the link to determine the optimal duplex mode and speed for the connection.

The driver then dynamically configures the interface to the values determined for the link.

1. Speed:

Speed is the rate of the interface, usually listed in megabits per second (Mbps). Common Ethernet speeds include 10 Mbps, 100 Mbps, and 1,000 Mbps. 1,000 Mbps Ethernet is also referred to as Gigabit Ethernet.

Attenuation is the reduction in optical signal (amplitude and intensity) as it propagates along a fiber.

Attenuation is due to absorption, scattering and other loss mechanisms (such as impurities, bending, and coupling). Attenuation is usually expressed in dB or as a rate of loss per unit distance (dB/km).

The following picture shows the three wavelength windows being used in fiber optic communications.