After reading this enough physical layer

1. The basic concept of the physical layer

• The physical layer transport address how data bit stream, rather than to a specific transmission medium on a computer connected to various transmission media.
• The main task of the physical layer: interfaces for determining characteristics of transmission media.
  Namely:
  Mechanical properties: the interface shape, size, number of wire
  electrical characteristics: a predetermined voltage range
  feature: Example 1 represents a predetermined -5V represents 0,5V
  process characteristics: establishing a predetermined respective connection members associated work steps. (Also known as procedural characteristics)

2. Basics of data communication

• Typical data communication model:
  
• Related terms:
  Data: transport entity message.
  Destination communication message is transmitted.
  Signal (signal): performance of an electrical or electromagnetic data.
  Analog signal: the value representing the message parameter is continuous.
  Digital signal: the value of the parameter representative of the message is discrete.
  Symbol (code):
  
• Channel: transmitting a media message indicates to the one direction, say how often a communication line usually contains a channel message transmitting and receiving an information channel.
• 
• 
• Several basic methods of modulating a baseband signal:
  
  
  
  Differential Manchester encoding: 0 transition has not to 1.
  Manchester encoding: Intermediate 1 from high to low, from low to high is 0.
• :( actual channel bandwidth is limited, noise, interference and distortion)
  Nyquist criterion: assuming ideal conditions in order to avoid intersymbol interference, the upper limit of the transmission rate of the symbols (2WBaud).
  
  
• SNR:

3. The following physical layer transmission medium

• Cable
• 8 shielded twisted pair lines outside the metal layer.
  
  
  
  Hubs full hair, does not determine the source and destination addresses and unsafe. Bisection bandwidth,

4. The channel multiplexing

Channel (transmission to the receiving end)

• Frequency Division Multiplexing
  
  call is frequency-division multiplexing (can continue to reuse).
• Time division multiplexing: all users occupy the same bandwidth at different times. Time division multiplexing, when the data should not put it to put data, others impossible, a waste of resources.
• Statistical time division multiplexing:
  not by time, to mark unity, solve the issue on appeal.
• Code Division Multiplexing (CDM)
  mobile communications using code division multiplexing is used. Using the same frequency.
  • The one bit time divided into m short intervals called chips.

The digital transmission system

6. The broadband access technology

the xDSL (communication existing analog telephone subscriber line using digital technology)

low phone, computer access frequency.



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