MAC
frame check sequence field
Physical layer which is the first layer in OSI reference model is responsible for signal encoding and decoding.
Digital signals are virtually always transmitted using a continuous (analog) waveform. Even a signal that is called "digital" is actually analog in practice. When a digital signal is transmitted over short range (inside an integrated circuit, on a computer motherboard, etc.) we talk about it being digital, but inspection of the actual waveform with an oscilloscope will reveal that it is not just two different voltage levels. But it is "mostly digital" and can be treated as such by circuit elements that are expecting digital signals. That is, we call it a "digital signal" but it isn't perfectly digital (two different values). It is actually theoretically impossible to transmit a pure digital signal. Doing so would require an infinite energy pulse to create the step functions. In practice, the limiter to making a signal that is almost perfectly digital tends to be the "load" and the transmission channel, which both have resistance, capacitance and inductance that make even a very abrupt signal smooth out a little. When digital signals are transmitted over relatively long distances, they are sometimes deliberately "encoded" onto an analog carrier. There are various methods for doing this, such as frequency modulation, amplitude modulation, phase modulation, or combinations. There can even be multiple layers of encoding to implement features such as error detection and error correction. So if you were to inspect the signal that is transmitted, you would see an obvious analog signal, but the information that is hidden in it is an encoded digital signal that will be re-formed at the receiver.
Why digital communications and what its advantages over analog communication ,first you have to know what is the difference between analog signal and digital signal. Analog signal analog signal is continuous time signal i.e. it has a value at any moment of time and it has infinite number of valus , such as dinusoidal signal ,you can substitute X with any value and you will have an value in Y in the follwing sin relation Y=sin(X). 1-Noise and destortion immunity:-when analog signal is transmitted in free space for long distances it will be distorted and no an ideal recovery done in receiver to recover the exact signal which transmitted ,but in digital communication digital signal consist of 2 levels only zero or one (not like the analog one , it has infinite numbers of values or levels at each period of time),so digital signal can be recovered easily and excactly like transmitted one. Hint : Device that used to pattially recover the analog signal after a certain distance is called repeater ,from its name it receives transmitted analog signal and filter it and amplify it and transmitt it),but in digital transmission it is different ,the device used for recovering digital signal which transmitted from acertain distance is called regenerative repeaters ,it receives transmitted digital signal and recover it to regenrate a new exact signal like received one then retransmitt it for further distance. 2-More privacy and security due to encryption. 3-Error detection techniques can be used and correction as well. 4-Easy for processing and applying multiplexing techniques. 5-Low cost. 6-Transmission rate can be changed easily. 7-Digital hardware implementation is flexible and permits the use of micrprocessors, digital switching elements and layer scale. Thanks for reading H.M.S
fiber optic cables, coaxial cables, and twisted pair cables.
MAC
People do not have the physical organs to detect microwaves.
the digital signal is converted to analog signal after using by transmitted antenna
When several signal transmitted simultaneously. this is called multiplexing of signals.many signal are combined into one and then they transmitted.
Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. That is the definition of Layer 1.
Information refers to data that has been processed and organized to convey meaning or knowledge, while a signal is a physical representation of information that is transmitted through a medium such as sound waves or electrical pulses. In other words, information is the content being communicated, while a signal is the form in which that information is transmitted.
Analog signals are transmitted as electrical waves.
Reflection of a transmitted signal is the basic premise of radar and sonar.
Yes, this is a true statement. A TV channel is most often characterized by the frequency of its transmitted signal.
Radio Waves
the signal goes out of sink due to refraction
by analog to digital,digital to analog signal