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