Data Communication Network

331: STUDY DATA COMMUNICATIONS AND NETWORKS

331: STUDY DATA COMMUNICATIONS AND NETWORKS

1. Discuss computer networks (5 hrs) 2. Discuss data communications (15 hrs)

331.2: Discuss Data Communications PERFORMANCE STANDARD

◦ Given a network system, identify and illustrate the different data communications components clearly

Objectives:◦ Define elements of a communication system◦ Define data communications◦ Discuss various types of transmission media and

their characteristics◦ Discuss encoding of information for transmission◦ Discuss types of signal & their characteristics◦ Relate data capacity of a channel and bandwidth◦ Classify media based on bandwidth◦ Discuss channel organization

SKILL AREA 331.2.3

Relate data capacity of a channel and

bandwidth

Simplified Data Communications Model

Modulation and Multiplexing are electronic techniques for transmitting information efficiently from one place to another.

Modulation makes the information signal more compatible with the medium.

Multiplexing allows more than one signal to be transmitted concurrently over a single medium.

Modulation and Multiplexing

Channel: The amount of bandwidth that a signal occupies in the radio frequency spectrum.

Channel Capacity: The maximum possible rate information rate that data can be transmitted over a given communication path or channel under given condition.

Data Rate Limit

A very important consideration in data communications is how fast we can send data, in bits per second, over a channel.

The Data rate depends on three factors:◦ The bandwidth available.◦ The level of the signals we use.◦ The quality of the channel (the level of noise).

Data Rate Limit

Two theoretical formulas were developed to calculate the data rate:

◦ Nyquist bit rate for a noiseless channel BitRate = 2 * bandwidth * log2 L

◦ Shannon Capacity for a noisy channel Capacity = bandwidth * log2 (1 + SNR)

Data Rate Limit

Bandwidth: The narrow frequency range over which the signal amplitude in a circuit is highest.

The term of Bandwidth can be used in two different measuring value: bandwidth in hertz and bandwidth in bits per second.

Data Rate Limit

Bandwidth in Hertz: It is the range of frequencies contained in a composite signal or the range of frequencies a can pass. For example: We can say the bandwidth of a subscriber telephone line is 4kHz.

Bandwidth in Bits per Seconds: It refer to the speed of bit transmission in a channel, a link or even a network can transmit. For example: One can say the bandwidth of a Fast Ethernet network is a maximum of 100 Mbps. This means that the network can send 100 Mbps.

Bandwidth

There is an explicit relationship between the bandwidth in hertz and bandwidth in bits per seconds.

Basically, an increase in bandwidth in hertz means an increase in bandwidth in bits per second.

The relationship depends whether we have baseband transmission or broadband transmission.

Relationship between bandwidth in Hertz and bandwidth in bps

Transmission of digital or analog signal without modulation using a low-pass channel. Low pass channel is a channel with bandwidth starts from zero.

Baseband transmission

Transmission of signals using modulation of a higher frequency signal.

It means changing the digital signal to analog for transmission and modulation allows us to use a bandpass channel – a channel with a bandwidth that does not start with zero.

Broadband Transmission

Broadband Transmission

Modulation of a digital signal for a transmission on a bandpass channel

The number of digital values the channel can convey in one second.

A digital communications channel has limitations that determine how often the signal can change states over a period.

These limitations establish the maximum rate at which data can flow through the channel.

Digital Channel Capacity

A variety of baseband signaling techniques are used to convey information or data.

Digital systems may have more than two discrete changes as shown in the Figure.

A binary system has only two discrete energy levels

A digital system can have many discrete energy levels.

Digital Channel Capacity

Digital system electrical signals

Digital signal distortion and attenuation with distance

Bandwidth versus length characteristics as shown in the previous Figure can be used to determine the length of channel they want to use for specific applications.

high-volume application requires a high bandwidth such as a direct connection between two mainframe computers, a vendor can limit the length of the communications channel to a short distance.

A low-volume application such as the connection between a personal computer and a low speed printer, the vendor can specify a longer channel

Digital signal

Medium bandwidth versus length

Provide devices that regenerate a digital signal.

Repeaters receive the signal and rebuild it to its original strength and shape.

The repeater catches the signal before it degrades to the point that it is unusable.

Digital signal cannot be amplified to increase their distance range in a channel.

Digital Signal Regeneration

If you amplify a digital signal, you also amplify the noise that contaminated the signal.

The amplified noise can become a substantial part of the signal.

A repeater removes the noise from a signal while it is regenerating the signal.

Digital Signal Regeneration

Digital Signal Regeneration

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