CIT 307 Online Data Communications
description
Transcript of CIT 307 Online Data Communications
CIT 307 OnlineData Communications
Digital TransmissionDigital Transmission
Module 5Module 5Kevin Siminski, InstructorKevin Siminski, Instructor
Linecoding
Characteristics Line Coding Schemes Other Schemes
Line Coding
Signal level versus data level
DC Component
Lack of synchronization
Why is timing important?
In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps?
Why timing (continued)?
At 1 Kbps:– 1000 bits sent 1001 bits received1 extra bps
At 1 Mbps: – 1,000,000 bits sent 1,001,000 bits received1000 extra
bps
Line Coding
Unipolar Encoding
Unipolar encoding uses only one voltage level.
Unipolar Encoding
Polar Encoding
Polar encoding uses two voltage levels Polar encoding uses two voltage levels (positive and negative).(positive and negative).
Polar Encoding
Polar encoding
In NRZ-L the level of the signal is dependent In NRZ-L the level of the signal is dependent upon the state of the bit.upon the state of the bit.
In NRZ-L the level of the signal is In NRZ-L the level of the signal is dependent upon the state of the bit.dependent upon the state of the bit.
NRZ-L & NRZ-I encoding
RZ encoding
Synchronization
A good encoded digital signal must contain A good encoded digital signal must contain a provision for synchronization. a provision for synchronization.
Timing/synchronization is one of the most Timing/synchronization is one of the most important elements in Layer 1important elements in Layer 1
Bi-polar Encoding
In bipolar encoding, we use three levels: In bipolar encoding, we use three levels: positive, zero, and negative. This is the positive, zero, and negative. This is the
most common encoding mechanism used most common encoding mechanism used in North America transmission systemsin North America transmission systems
Bi-polar AMI encoding
Data transmission
Parallel Transmission
Serial Transmission
Asynchronous Transmission
Asynchronous here means “asynchronous Asynchronous here means “asynchronous at the byte level,” but the bits are still at the byte level,” but the bits are still synchronized; their durations are the synchronized; their durations are the
same.same.
Asynchronous Transmission
Synchronous Transmission
In synchronous transmission, In synchronous transmission, we send bits one after another without we send bits one after another without
start/stop bits or gaps. start/stop bits or gaps. It is the responsibility of the receiver to It is the responsibility of the receiver to
group the bits.group the bits.
Synchronous Transmission
Important point to consider
Timing/Synchronization is the single most important element in a data communications network.
Encoding transforms 0’s & 1’s into electronic pulses.
The North American standard used today is Bi-Polar encoding