Digital Transmission and Broadband Access Technologies
Basic Concepts of Physical Layer
The physical layer is lowest level of computer network communication. It's responsible for how network devices are connected and how data is sent from one point to anor. This layer doesn't deal with specifics of transmission medium but rar focuses on features of interface with transmission medium.，这事儿我得说道说道。
Tasks of Physical Layer
Define characteristics of interface with transmission medium, such as:
Mechanical characteristics: Specify shape, size, pin number, and arrangement of interface connectors, as well as fixing and locking devices.
Electrical characteristics: Specify voltage range on interface cable.
Functional characteristics: Specify sequence of occurrence of various possible events for different functions.
Procedural characteristics: Specify sequence of operations for different functions.
Basics of Data Communication
说到底。 Data communication is process of sending and receiving data between two or more computers. It involves several components, such as:
Data Communication Systems Model
Types of Channels: Analog, Digital, and Hybrid
Channel Capacity: The maximum amount of data that can be transmitted over a channel in a given time.
Guided and Unguided Transmission Media
我怀疑... Guided media use physical wires or cables to carry signals, while unguided media use electromagnetic waves to transmit signals. Examples of guided media include:
Twisted Pair: Consists of two insulated copper wires twisted toger.
Coaxial Cable: Consists of a central conductor, an insulating layer, a metallic shield, and an outer insulating layer.
Optical Fiber: Made of glass or plastic and uses light to carry signals.
Examples of unguided media include:
Wireless Transmission: Uses radio waves to transmit signals.
Radio Transmission: Uses radio waves to transmit signals through air.
Multiplexing Techniques
交学费了。 Multiplexing is process of combining multiple signals into a single signal for transmission over a shared medium. There are several types of multiplexing techniques:
Frequency Division Multiplexing : Divides frequency spectrum into multiple channels.
Time Division Multiplexing : Divides transmission time into multiple slots for each signal.
Statistical Time Division Multiplexing : Dynamic allocation of time slots to signals.
Wavelength Division Multiplexing : Combines multiple optical signals by using different wavelengths of light.
Coded Division Multiple Access : Assigns a unique code to each signal to allow multiple signals to be transmitted simultaneously over same frequency band.
Digital Transmission and Broadband Access Technologies
Digital transmission involves sending digital signals over a communication channel. It is more reliable and less susceptible to noise compared to analog transmission. Examples of digital transmission technologies include:
ADSL: Asymmetric Digital Subscriber Line
HFC: Hybrid Fiber Coaxial
FTTx: Fiber to x, where x can be curb, home, premise, or building.
Conclusion
差不多得了... This article has provided a basic understanding of physical layer and its role in communication signal transmission. By grasping concepts of physical layer, data communication, transmission media, and multiplexing techniques, we can better understand how data is transmitted over a network.
Remember, physical layer is foundation of all network communication, and understanding its principles is crucial for anyone involved in networking or computer science.，我懂了。
