Layer 1 - Physical layer
The physical layer deals with the transfer of bits on physical components, such, as a coaxial cable, a twisted pair cable, or an optical fiber cable. The characteristics of the physical medium, such as attenuation174 crosstalk, impedance 175, etc., relate to this layer. To remember Layer 1 in as few words as possible, think of information transmission speeds and media types. One of the major characteristics of the communication channel is bandwidth176.
Bandwidth is the measure of how much data can flow from one computer to another in a given amount of time. The unit of measurement is bits per second (bps) and is equal to 1 bit per one second.
Throughput is the actual measured bandwidth at a specific period. The throughput is often less then the maximum possible bandwidth of the medium that is being used.
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