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Point-to-Point Point-to-point networks contains exactly two hosts such as computer, switches, routers, or servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice versa. If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly.

Bus Topology In case of Bus topology, all devices share single communication line or cable. Bus topology may have problem while multiple hosts sending data at the same time. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning. The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from the line.

Star Topology All hosts in Star topology are connected to a central device, known as hub device, using a point-to-point connection. That is, there exists a point to point connection between hosts and hub. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts takes place through only the hub. Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple. Ring Topology In ring topology, each host machine connects to exactly two other machines, creating a circular network structure.

When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable.

Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring. Mesh Topology In this type of topology, a host is connected to one or multiple hosts. This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection with few hosts only.

It provides the most reliable network structure among all network topologies. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all. Tree Topology Also known as Hierarchical Topology, this is the most common form of network topology in use presently. This topology imitates as extended Star topology and inherits properties of Bus topology.

Mainly in LANs, a network is bifurcated into three types of network devices. The lowermost is access-layer where computers are attached. The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer. The highest layer is known as core layer, and is central point of the network, i. Similar to the Bus topology, if the root goes down, then the entire network suffers even though it is not the single point of failure.

Every connection serves as point of failure, failing of which divides the network into unreachable segment. Daisy Chain This topology connects all the hosts in a linear fashion. Similar to Ring topology, all hosts are connected to two hosts only, except the end hosts. Means, if the end hosts in daisy chain are connected then it represents Ring topology. Each link in daisy chain topology represents single point of failure. Every link failure splits the network into two segments.

Every intermediate host works as relay for its immediate hosts. Hybrid Topology A network structure whose design contains more than one topology is said to be hybrid topology. Hybrid topology inherits merits and demerits of all the incorporating topologies. The combining topologies may contain attributes of Star, Ring, Bus, and Daisy-chain topologies.

Most WANs are connected by means of Dual-Ring topology and networks connected to them are mostly Star topology networks. Internet is the best example of largest Hybrid topology. To ease network engineering, the whole networking concept is divided into multiple layers. Each layer is involved in some particular task and is independent of all other layers.

But as a whole, almost all networking tasks depend on all of these layers. Layers share data between them and they depend on each other only to take input and send output. Layered Tasks In layered architecture of Network Model, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work. In layered communication system, one layer of a host deals with the task done by or to be done by its peer layer at the same level on the remote host.

The task is either initiated by layer at the lowest level or at the top most level. If the task is initiated by the topmost layer, it is passed on to the layer below it for further processing. The lower layer does the same thing, it processes the task and passes on to lower layer.

If the task is initiated by lowermost layer, then the reverse path is taken. Every layer clubs together all procedures, protocols, and methods which it requires to execute its piece of task.

All layers identify their counterparts by means of encapsulation header and tail. This model has seven layers: Application Layer: This layer is responsible for providing interface to the application user. This layer encompasses protocols which directly interact with the user. Presentation Layer: This layer defines how data in the native format of remote host should be presented in the native format of host.

Session Layer: This layer maintains sessions between remote hosts. Transport Layer: This layer is responsible for end-to-end delivery between hosts. Network Layer: This layer is responsible for address assignment and uniquely addressing hosts in a network. Data Link Layer: This layer is responsible for reading and writing data from and onto the line.

Link errors are detected at this layer. Physical Layer: This layer defines the hardware, cabling, wiring, power output, pulse rate etc. This defines Internet Model which contains four layered architecture. OSI Model is general communication model but Internet Model is what the internet uses for all its communication.

The internet is independent of its underlying network architecture so is its Model. This model has the following layers: Application Layer: This layer defines the protocol which enables user to interact with the network. Transport Layer: This layer defines how data should flow between hosts. This layer ensures data delivered between hosts is in-order and is responsible for end- to-end delivery.

This layer facilitates host addressing and recognition. This layer defines routing. Link Layer: This layer provides mechanism of sending and receiving actual data. Unlike its OSI Model counterpart, this layer is independent of underlying network architecture and hardware. Later when all networks merged together and formed internet, the data used to travel through public transit network.

Common people may send the data that can be highly sensitive such as their bank credentials, username and passwords, personal documents, online shopping details, or confidential documents.

All security threats are intentional i. Security threats can be divided into the following categories: Interruption Interruption is a security threat in which availability of resources is attacked. For example, a user is unable to access its web-server or the web-server is hijacked. Privacy-Breach In this threat, the privacy of a user is compromised. Someone, who is not the authorized person is accessing or intercepting data sent or received by the original authenticated user.

Integrity This type of threat includes any alteration or modification in the original context of communication. The attacker intercepts and receives the data sent by the sender and the attacker then either modifies or generates false data and sends to the receiver.

The receiver receives the data assuming that it is being sent by the original Sender. Authenticity This threat occurs when an attacker or a security violator poses as a genuine person and accesses the resources or communicates with other genuine users.

But steps can be taken to secure data while it travels in unsecured network or internet. The most widely used technique is Cryptography. After the data is encrypted, it is sent on the public domain to the receiver. Because the receiver knows and has the Secret Key, the encrypted data packets can easily be decrypted. In Secret Key encryption, it is required to have a separate key for each host on the network making it difficult to manage.

Public Key Encryption In this encryption system, every user has its own Secret Key and it is not in the shared domain. The secret key is never revealed on public domain. Along with secret key, every user has its own but public key. Public key is always made public and is used by Senders to encrypt the data.

When the user receives the encrypted data, he can easily decrypt it by using its own Secret Key. Message Digest In this method, actual data is not sent; instead a hash value is calculated and sent.

The other end user, computes its own hash value and compares with the one just received. If both hash values are matched, then it is accepted; otherwise rejected. Example of Message Digest is MD5 hashing. It is mostly used in authentication where user password is cross checked with the one saved on the server. Physical layer is the only layer of OSI network model which actually deals with the physical connectivity of two different stations. This layer defines the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc.

Physical layer provides its services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts them to electrical pulses, which represent binary data.

The binary data is then sent over the wired or wireless media. Signals When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk. Both analog and digital data can be represented in digital or analog signals. Digital Signals Digital signals are discrete in nature and represent sequence of voltage pulses.

Digital signals are used within the circuitry of a computer system. Analog Signals Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves. Transmission Impairment When signals travel through the medium, they tend to deteriorate. This may have many reasons as given: Attenuation For the receiver to interpret the data accurately, the signal must be sufficiently strong. When the signal passes through the medium, it tends to get weaker.

As it covers distance, it loses strength. Dispersion As signal travels through the media, it tends to spread and overlaps. The amount of dispersion depends upon the frequency used. Delay distortion Signals are sent over media with pre-defined speed and frequency. If the signal speed and frequency do not match, there are possibilities that signal reaches destination in Smartzworld.

In digital media, this is very critical that some bits reach earlier than the previously sent ones. Noise Random disturbance or fluctuation in analog or digital signal is said to be Noise in signal, which may distort the actual information being carried.

Noise can be characterized in one of the following class: Thermal Noise Heat agitates the electronic conductors of a medium which may introduce noise in the media.

Up to a certain level, thermal noise is unavoidable. Intermodulation When multiple frequencies share a medium, their interference can cause noise in the medium. Intermodulation noise occurs if two different frequencies are sharing a medium and one of them has excessive strength or the component itself is not functioning properly, then the resultant frequency may not be delivered as expected.

Crosstalk This sort of noise happens when a foreign signal enters into the media. This is because signal in one medium affects the signal of second medium. Impulse This noise is introduced because of irregular disturbances such as lightening, electricity, short-circuit, or faulty components.

Digital data is mostly affected by this sort of noise. Transmission Media The media over which the information between two computer systems is sent, called transmission media. Transmission media comes in two forms. In this media, the sender and receiver are directly connected and the information is send guided through it.

Unguided Media Wireless or open air space is said to be unguided media, because there is no connectivity between the sender and receiver. Information is spread over the air, and anyone including the actual recipient may collect the information.

Channel Capacity The speed of transmission of information is said to be the channel capacity. We count it as data rate in digital world. It depends on numerous factors such as: Smartzworld. Multiplexing Multiplexing is a technique to mix and send multiple data streams over a single medium.

This technique requires system hardware called multiplexer MUX for multiplexing the streams and sending them on a medium, and de-multiplexer DMUX which takes information from the medium and distributes to different destinations. Networks have interconnecting devices, which receives data from directly connected sources, stores data, analyze it and then forwards to the next interconnecting device closest to the destination. Switching can be categorized as: Smartzworld.

For a computer to use the data, it must be in discrete digital form. Similar to data, signals can also be in analog and digital form. To transmit data digitally, it needs to be first converted to digital form. Digital-to-Digital Conversion This section explains how to convert digital data into digital signals. It can be done in two ways, line coding and block coding. For all communications, line coding is necessary whereas block coding is optional. Line Coding The process for converting digital data into digital signal is said to be Line Coding.

Digital data is found in binary format. It is represented stored internally as series of 1s and 0s. Digital signal is denoted by discreet signal, which represents digital data. There are three types of line coding schemes available: Smartzworld. In this case, to represent binary 1, high voltage is transmitted and to represent 0, no voltage is transmitted.

It is also called Unipolar-Non-return-to-zero, because there is no rest condition i. Polar Encoding Polar encoding scheme uses multiple voltage levels to represent binary values. Generally, positive voltage represents 1 and negative value represents 0. It is also NRZ because there is no rest condition. Signals change during bits not between bits. Bit time is divided into two halves. It transits in the middle of the bit and changes phase when a different bit is encountered.

It also transits at the middle of the bit but changes phase only when 1 is encountered. Bipolar Encoding Bipolar encoding uses three voltage levels, positive, negative, and zero. Zero voltage represents binary 0 and bit 1 is represented by altering positive and negative voltages. Block Coding To ensure accuracy of the received data frame, redundant bits are used. For example, in even-parity, one parity bit is added to make the count of 1s in the frame even.

This way the original number of bits is increased. It is called Block Coding. Block coding involves three steps: 1. Division 2. Substitution 3. Analog-to-Digital Conversion Microphones create analog voice and camera creates analog videos, which are treated is analog data.

To transmit this analog data over digital signals, we need analog to digital conversion. Analog data is a continuous stream of data in the wave form whereas digital data is discrete.

PCM is one of the most commonly used method to convert analog data into digital form. Sampling The analog signal is sampled every T interval. Most important factor in sampling is the rate at which analog signal is sampled. According to Nyquist Theorem, the sampling rate must be at least two times of the highest frequency of the signal.

Quantization Sampling yields discrete form of continuous analog signal. Every discrete pattern shows the amplitude of the analog signal at that instance. The quantization is done Smartzworld. Quantization is approximation of the instantaneous analog value.

Encoding In encoding, each approximated value is then converted into binary format. Transmission Modes The transmission mode decides how data is transmitted between two computers. The binary data in the form of 1s and 0s can be sent in two different modes: Parallel and Serial. Parallel Transmission The binary bits are organized into groups of fixed length. Both sender and receiver are connected in parallel with the equal number of data lines.

Both computers distinguish between high order and low order data lines. The sender sends all the bits at once on all lines. Because the data lines are equal to the number of bits in a group Smartzworld. Advantage of Parallel transmission is high speed and disadvantage is the cost of wires, as it is equal to the number of bits sent in parallel. Serial Transmission In serial transmission, bits are sent one after another in a queue manner. Serial transmission requires only one communication channel.

Serial transmission can be either asynchronous or synchronous. Asynchronous Serial Transmission It is named so because there is no importance of timing. Data-bits have specific pattern and they help receiver recognize the start and end data bits. For example, a 0 is prefixed on every data byte and one or more 1s are added at the end. Two continuous data-frames bytes may have a gap between them.

Synchronous Serial Transmission Timing in synchronous transmission has importance as there is no mechanism followed to recognize start and end data bits. Data bits are sent in burst mode without maintaining gap between bytes 8- bits.

Single burst of data bits may contain a number of bytes. Therefore, timing becomes very important. It is up to the receiver to recognize and separate bits into bytes. The advantage of synchronous transmission is high speed, and it has no overhead of extra header and footer bits as in asynchronous transmission. There can be two cases according to data formatting. Bandpass: The filters are used to filter and pass frequencies of interest. A bandpass is a band of frequencies which can pass the filter.

Low-pass: Low-pass is a filter that passes low frequencies signals. When digital data is converted into a bandpass analog signal, it is called digital-to- analog conversion.

When low-pass analog signal is converted into bandpass analog signal, it is called analog-to-analog conversion. Digital-to-Analog Conversion When data from one computer is sent to another via some analog carrier, it is first converted into analog signals. Analog signals are modified to reflect digital data. An analog signal is characterized by its amplitude, frequency, and phase.

There are three kinds of digital-to-analog conversions: Amplitude Shift Keying In this conversion technique, the amplitude of analog carrier signal is modified to reflect binary data. When binary data represents digit 1, the amplitude is held; otherwise it is set to 0.

Both frequency and phase remain same as in the original carrier signal. Frequency Shift Keying Smartzworld. This technique uses two frequencies, f1 and f2. One of them, for example f1, is chosen to represent binary digit 1 and the other one is used to represent binary digit 0.

Both amplitude and phase of the carrier wave are kept intact. Phase Shift Keying In this conversion scheme, the phase of the original carrier signal is altered to reflect the binary data. When a new binary symbol is encountered, the phase of the signal is altered. Amplitude and frequency of the original carrier signal is kept intact. Quadrature Phase Shift Keying Smartzworld. This is done in two different phases.

The main stream of binary data is divided equally into two sub-streams. The serial data is converted in to parallel in both sub-streams and then each stream is converted to digital signal using NRZ technique.

Later, both the digital signals are merged together. Analog-to-Analog Conversion Analog signals are modified to represent analog data. This conversion is also known as Analog Modulation. Analog modulation is required when bandpass is used. Analog to analog conversion can be done in three ways: Amplitude Modulation In this modulation, the amplitude of the carrier signal is modified to reflect the analog data.

The amplitude of modulating signal analog data is multiplied by the amplitude of carrier frequency, which then reflects analog data.

The frequency and phase of carrier signal remain unchanged. Frequency Modulation In this modulation technique, the frequency of the carrier signal is modified to reflect the change in the voltage levels of the modulating signal analog data. Phase Modulation In the modulation technique, the phase of carrier signal is modulated in order to reflect the change in voltage amplitude of analog data signal.

Frequency of carrier is signal is changed made dense and sparse to reflect voltage change in the amplitude of modulating signal. Magnetic Media One of the most convenient way to transfer data from one computer to another, even before the birth of networking, was to save it on some storage media and transfer physical from one station to another.

For example, a bank has to handle and transfer huge data of its customer, which stores a backup of it at some geographically far-away place for security reasons and to keep it from uncertain calamities.

If the bank needs to store its huge backup data, then its transfer through internet is not feasible. The WAN links may not support such high speed.

Even if they do; the cost is too high to afford. In these cases, data backup is stored onto magnetic tapes or magnetic discs, and then shifted physically at remote places. Twisted Pair Cable A twisted pair cable is made of two plastic insulated copper wires twisted together to form a single media. Out of these two wires, only one carries actual signal and another is used for ground reference. The twists between wires are helpful in reducing noise electro-magnetic interference and crosstalk.

This makes it more indifferent to noise and crosstalk. UTP has seven categories, each suitable for specific use. In computer networks, Cat- 5, Cat-5e, and Cat-6 cables are mostly used. UTP cables are connected by RJ45 connectors. Coaxial Cable Coaxial cable has two wires of copper.

The core wire lies in the center and it is made of solid conductor. The core is enclosed in an insulating sheath. The second wire is wrapped around over the sheath and that too in turn encased by insulator sheath. This all is covered by plastic cover. Because of its structure, the coax cable is capable of carrying high frequency signals than that of twisted pair cable. The wrapped structure provides it a good shield against noise and cross talk.

Updated with the latest advances in the field, Jerry FitzGerald and Alan Dennis' 10th Edition of Business Data Communications and Networking continues to provide the fundamental concepts and cutting-edge coverage applications that students need to succeed in this fast-moving field.

Authors FitzGerald and Dennis have developed a foundation and balanced presentation from which new technologies and applications can be easily understood, evaluated, and compared. Business Data Communications and Networking, 14th Edition presents a classroom-tested approach to the subject, combining foundational concepts, practical exercises, and real-world case studies. The text provides a balanced, well-rounded presentation of data communications while highlighting its importance to nearly every aspect of modern business.

This fully-updated new edition helps students. As the world grows increasingly interconnected, data communications has become a critical aspect of business operations. Wireless and mobile technology allows us to seamlessly transition from work to play and back again, and the Internet of things has brought our appliances, vehicles, and homes into the network; as life increasingly.