Types of Networks
Network category is determined by its size, ownership, the distance it cover and its physical architecture. The types of networks are local-area networks and wide- area networks. The category into which a network falls is determined by its size. A LAN normally covers an area less than 2 miles, a WAN can be worldwide. Networks of a size in between are normally referred to as metropolitan area networks and span tens of miles.
Different layers of OSI model
The OSI model is a layered framework for the design of network systems that allows communication between all types of computer systems. It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network.
The different layers in OSI model are represented in the following figure.
Diffrent Layers of TCP/IP
TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.
The first four layers provide physical standards, network interfaces, internetworking, and transport functions that correspond to the first four layers of the OSI model. The three topmost layers in the OSI model, however, are represented in TCP/IP by a single layer called the application layer which is showing in the following figure.
Add a commentPeer-to-Peer Process:
Within a single machine, each layer calls upon the services of the layer just below it. Layer 3, for example, uses the services provided by layer 2 and provides services for layer 4. Between machines, layer x on one machine communicates with layer x on another machine. This communication is governed by an agreed-upon series of rules and conventions called protocols. The processes on each machine that communicate at a given layer are called peer-to-peer processes. Communication between machines is therefore a peer-to-peer process using the protocols appropriate to a given layer.
Add a commentFundamentals of Data and Signals
The major function of the physical layer is to move data in the form of electromagnetic signals across a transmission medium. Whether the data may be numerical statistics from another computer, sending animated pictures from a design workstation, or causing a bell to ring at a distant control center, you are working with the transmission of data across network connections.
Data can be analog or digital. The term analog data refers to information that is continuous, Digital data refers to information that has discrete states. For example, an analog clock that has hour, minute, and second hands gives information in a continuous form, the movements of the hands are continuous. On the other hand, a digital clock that reports the hours and the minutes will change suddenly from 8:05 to 8:06.
Add a commentDigital Signals
Information can also be represented by a digital signal. For example, a 1 can be encoded as a positive voltage and a 0 as zero voltage. A digital signal can have more than two levels. In this case, we can as zero voltage. A digital signal can have more than two levels. In this case, we can send more than 1 bit for each level. The following figure shows two signals, one with two levels and the other with four. In general, if a signal has L levels, each level needs log2L bits.
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Bit Rate:
The bit rate is the number of bits sent in Is, expressed in bits per second (bps).
The Bit Rate for the above diagram is 8bps and 16bps.
Bit Length:
The bit length is the distance one bit occupies on the transmission medium.
Bit length =propagation speed x bit duration
Based on Fourier analysis, a digital signal is a composite analog signal. The bandwidth is infinite.
A digital signal, in the time domain, comprises connected vertical and horizontal line segments. A vertical line in the time domain means a frequency of infinity (sudden change in time); a horizontal line in the time domain means a frequency of zero (no change in time). Going from a frequency of zero to a frequency of infinity (and vice versa) implies all frequencies in between are part of the domain.
Fourier analysis can be used to decompose a digital signal. If the digital signal is periodic, which is rare in data communications, the decomposed signal has a frequency domain representation with an infinite bandwidth and discrete frequencies. If the digital signal is non-periodic, the decomposed signal still has an infinite bandwidth, but the frequencies are continuous.
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Back to DCN Questions and Answers
Composite Signals In Data Communication
A single-frequency sine wave (simple sine wave) is not useful in data communications; we need to change one or more of its characteristics to make it useful. When we change one or more characteristics of a single, single--frequency signal, it becomes a composite signal made of many frequencies.
A composite signal can be periodic or non-periodic. A periodic composite signal can be decomposed into a series of simple sine waves with discrete frequencies, frequencies that have integer values (1, 2, 3, and so on). A non-periodic composite signal can be decomposed into a combination of an infinite number of simple sine waves with continuous frequencies, frequencies that have real values.
Add a commentDifferent Methods for Digital Signal Transmission
A digital signal periodic or non-periodic, is a composite analog signal with frequencies between zero and infinity. We can transmit a digital signal by using one of two different approaches: baseband transmission or broadband transmission (using modulation).
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