King Saud University College of Applied studies and Community Service 1301CT By: Nour Alhariqi 1nalhareqi st semester

 Data communications  Communications system  Communications system resources nalhareqi

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 Data communication.  Communication system.  Components of a data communications system.  Effectiveness of a data communications system.  Data forms.  Data transmission mode. 4nalhareqi

 Data communications are the exchange of data between two or more devices via some form of transmission medium such as a wire cable.  The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.  When we communicate, we are sharing information. 5nalhareqi

 For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs). 6nalhareqi

 A data communications system has five components: 7nalhareqi

1. Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2. Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. 3. Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 8nalhareqi

4. Transmission medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5. Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating. 9nalhareqi

 The effectiveness of a data communications system depends on four fundamental characteristics: Delivery AccuracyTimelinessJitter 10nalhareqi

 Delivery:  The system must deliver data to the correct destination.  Data must be received by the intended device or user and only by that device or user.  Accuracy:  The system must deliver the data accurately.  Data that have been altered in transmission and left uncorrected are unusable. 11nalhareqi

 Timeliness:  The system must deliver data in a timely manner.  Data delivered late are useless.  In the case of video and audio, timely delivery means : ▪ delivering data as they are produced, ▪ in the same order that they are produced, ▪ and without significant delay. ▪ This kind of delivery is called real-time transmission. 12nalhareqi

 Jitter:  Jitter refers to the variation in the packet arrival time.  It is the uneven delay in the delivery of audio or video packets.  For example, let us assume that video packets are sent every 3 ms. If some of the packets arrive with 3 ms delay and others with 4 ms delay, an uneven quality in the video is the result. 13nalhareqi

 Information today comes in different forms such as TextNumberAudioImagesVideo 14nalhareqi

 Communication between two devices can be: Simplex Half- duplex Full- duplex 15nalhareqi

 In simplex mode, the communication is unidirectional. Only one of the two devices on a link can transmit; the other can only receive.  In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.  In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously. 16nalhareqi

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 The three basic parts of the communication system: 18nalhareqi-2013

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A typical communication system can be modeled as : Source Sender Receiver 20nalhareqi-2013

 Source: Produces an input message; e.g. voice, picture, computer data etc.  If the input message is nonelectrical ( e.g. voice), it must be converted by an input transducer to an electrical signal (the Baseband signal / Message Signal) 21nalhareqi-2013

 A transducer, in simple terms is a device that converts one form of energy into another.  In the communication system, it convert the output of a source into an electrical signal that is suitable for transmission; e.g., a microphone and a video camera.  a human voice is sound wave which is a non- electrical form of energy, an input transducer will convert it into an electrical signal. 22nalhareqi-2013

 The Transmitter converts the electrical signal (the Baseband signal/Message Signal) into a form that is suitable for transmission through the transmission medium or channel by a process called modulation. 23nalhareqi-2013

 Channel can be wired or wireless.  While the signal is travelling through the channel(the medium) it is always attenuated (and the level of attenuation increases with distance).  Also, the signal shape may be changed during the transmission i.e. become ‘distorted’. 24nalhareqi-2013

 The signal is not only distorted by a channel, but it is also contaminated along the path by undesirable signals lumped under the broad term noise, which are random and unpredictable signals from causes external ( such interference from signals transmitted on nearby channels) and internal ( such noise resulted from thermal motion of electrons in conductors). 25nalhareqi-2013

 The function of the receiver is to recover the message signal contained in the signal received from the channel (received signal).  The received signal is a corrupted version of the transmitted signal.  So, the receiver reconstruct a recognizable form of the original message signal.  It reprocess the received signal by undoing the signal modifications ( demodulation) made at the transmitter and the channel. 26nalhareqi-2013

 The receiver output is fed to the output transducer, which convert the electrical signals that are received into a form that is suitable for the final destination; e.g., sound waves, images, etc. 27nalhareqi-2013

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 The rate and quality of data transmission depend on what?  Channel bandwidth.  Signal power.  Communication system resources. nalhareqi

 The fundamental parameters that control the rate and quality of data transmission in the communication system are:  Channel bandwidth.  Signal power. 32nalhareqi-2013

 The channel can transmit a range of frequencies with reasonable fidelity.  The bandwidth of a channel (B) is the width of the frequency band used to transmit the data.  It is the difference between the highest and lowest frequencies which the channel can carry. 33nalhareqi-2013

 If a channel can carry a signal which its frequency range from 0 to 5000 Hz (5 khz), the channel bandwidth B is 5 khz.  If a channel can carry frequencies between 200Hz and 4kHz, its bandwidth (the difference between those two frequencies) is 3.8kHz.  If a channel can carry frequencies between 10MHz and 100MHz, what is the channel bandwidth? 34nalhareqi-2013

 The rate of data transmission is directly proportional to B. 35nalhareqi-2013

 The signal power is related to the quality of transmission.  Increasing the signal power ( S ), reduces the effect of channel noise, and the information is received more accurately.  We measure noise relative to a signal in terms of the signal-to-noise ratio (SNR). 36nalhareqi-2013

 The SNR is the ratio of the average signal power to the average noise power.  A larger SNR also allows transmission over a longer distance.  In any event, a certain minimum SNR is necessary for communication. 37nalhareqi-2013

 So, in a communication system there are tow primary resources :  Channel bandwidth.  Transmission power (the average power of the transmitted signal ).  A general system design objective is to use these resources as efficiently as possible. 38nalhareqi-2013

 In most communication channels, one resource may be considered more important than the other.  We may therefore classify communication channel as power limited or band limited.  Telephone channel  band limited.  Satellite channel  power limited. 39nalhareqi-2013