What is bit-level transmission?

Bit-level transmission is the process by which data is transmitted one bit at a time (0 or 1) as a physical signal over a communication channel.

Put simply: bit-level transmission is the sequential sending of zeros and ones from one device to another.

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#What "bit" means in bit-level transmission

A bit is the smallest unit of information:

• 0 or 1

Example of a bit stream:

10110010

The physical layer does not know whether this is:

• text
• an image
• video
• an IP packet

To it, this is simply a set of bits.

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#How bit-level transmission happens

1. The device takes a stream of bits
2. Each bit is converted into a signal:

• an electrical pulse
• a light pulse
• a radio signal

3. The signal is transmitted over the medium (cable, fiber, air)
4. The receiver converts the signal back into bits

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#What bit-level transmission looks like in different media

#Copper cable

• 1 is a high voltage level
• 0 is a low voltage level

#Fiber optic

• 1 means light is present
• 0 means no light

#Wireless communication

• 0 and 1 are encoded as changes in the radio wave (frequency, phase, amplitude)

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#Important point for interviews

Bit-level transmission ≠ packet transmission

• bit-level transmission is the physical layer
• frames are the data link layer
• packets are the network layer

The physical layer:

• transmits bits
• does not know the structure of the data
• does not check for errors
• does not understand addresses

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#Simple analogy

Morse code:

• a short signal is 0
• a long signal is 1

What is transmitted is the signal; the meaning appears later.

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#Briefly, for the interview

Bit-level transmission is the transmission of data as a sequence of bits (0 and 1), converted into physical signals, without any understanding of their structure or meaning.