331: STUDY DATA COMMUNICATIONS AND NETWORKS

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

 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

Relate data capacity of a channel and bandwidth

 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.

 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.

 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).

 Two theoretical formulas were developed to calculate the data rate: ◦ Nyquist bit rate for a noiseless channel  BitRate = 2 * bandwidth * log 2 L ◦ Shannon Capacity for a noisy channel  Capacity = bandwidth * log 2 (1 + SNR)

 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.

 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.

 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.

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

 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.

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.

 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.

 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

 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.

 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.

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