Signal Transmission:
Signaling is the way data is transmitted across the medium. It uses electrical energy to communicate.
Two types of signaling:
Encoding data in a digital signal is called encoding schemes.
- Current-state encoding
- State-transition encoding
- In current-state encoding strategies, data is encoded by the presence or absence of a signal characteristics or state.
- The signal is monitored periodically by network
- State-transition encoding method use transitions in the signal to represent data.
- Presence of transition represents a 1 and the absence of transition indicate a 0.
State-transition encoding schemes:
- Bipolar-Alternative Mark Inversion (AMI)
- Non-Return-to-Zero (NRZ)Manchester
- Differential Manchester
- Biphase Space (FM-0)
- Comparing Signaling Methods
Advantages of digital signaling:
- Fewer errors from noise and interference
- Uses less expensive equipment
- Suffer from attenuation
- Less attenuation than digital signal
- Can be multiplexed to increase bandwidth
Disadvantages of analog signaling:
- More prone to errors from noise and interference
Bit Synchronization:
The coordination of signal measurement timing is called bit synchronization.
Two major method of bit synchronization:
- Asynchronous bit synchronization
- Synchronous bit synchronization
Asynchronous bit synchronization:
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| Asynchronous bit synchronization |
Asynchronous communication requires that messages begin with a start bit so that the receiving device can synchronize its internal clock with the timing of the message.
It is normally short and the end of the message is signaled by a stop bit.
Synchronous bit synchronization:
Synchronous communication requires that some kind of clocking mechanism be put into place to keep the clocks of the sender and receiver synchronized.
Methods used for synchronous timing coordination:
- Guaranteed state change
- Separate clock signal
- Oversampling
Baseband and broadband Transmission
Baseband: use the entire media bandwidth for a single channel. Commonly used for digital signaling. Most LANs use baseband signaling.
Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a single transmission medium.
Broadband: Provide the entire media bandwidth into multiple channels. Since each channel can carry a different analog signal, broadband networks support multiple simultaneous conversations over a single transmission medium.
