Explain the term simplex, half-duplex and full-duplex used in communication dialog mode

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Explain the term simplex, half-duplex and full-duplex used in communication dialog mode.



In simplex operation, a network cable or communications channel can only send information in one direction; it's a “one-way street”. A good example would be your keyboard to your CPU. The CPU never needs to send characters to the keyboard but the keyboard always sends characters to the CPU. In many cases, Computers almost always send characters to printers, but printers usually never send characters to computers (there are exceptions, some printers do talk back). Simplex requires only one lane (in the case of serial).



Technologies that employ half-duplex operation are capable of sending information in both directions between two nodes, but only one direction or the other can be utilized at a time. This is a fairly common mode of operation when there is only a single network medium (cable, radio frequency and so forth) between devices. The only advantage that Half-Duplex would have is the single lane or single track is cheaper then the double lane or double track.

For example, in conventional Ethernet networks, any device can transmit, but only one may do so at a time. 



In full-duplex operation, a connection between two devices is capable of sending data in both directions simultaneously. Full-duplex channels can be constructed either as a pair of simplex links (as described above) or using one channel designed to permit bidirectional simultaneous transmissions. A full-duplex link can only connect two devices, so many such links are required if multiple devices are to be connected together.

Explain the term analog and digital signal.

An analog signal is a continuous signal that contains time-varying quantities. Unlike a digital signal, which has a discrete value at each sampling point, an analog signal has constant fluctuations. The public dial-up service supports analogue signals. Analogue signals are what we encounter every day of our life. Speech is an analogue signal, and varies in amplitude (volume), frequency (pitch), and phase.

The three main characteristics of analogue signals are,

  • Amplitude

This is the strength of the signal. It can be expressed a number of different ways (as volts, decibels). The higher the amplitude, the stronger (louder) the signal. 

signal amplitude

This is the rate of change the signal undergoes every second, expressed in Hertz (Hz), or cycles per second.


This is the rate at which the signal changes its relationship to time, expressed as degrees. One complete cycle of a wave begins at a certain point, and continues till the same point is reached again. Phase shift occurs when the cycle does not complete, and a new cycle begins before the previous one has fully completed.


Digital Signals

A digital signal refers to an electrical signal that is converted into a pattern of bits. Unlike an analog signal, which is a continuous signal that contains time-varying quantities, a digital signal has a discrete value at each sampling point. Digital signals are the language of modern day computers. Digital signals comprise only two states. These are expressed as ON or OFF, 1 or 0 respectively. Examples of devices having TWO states in the home are,

  • Light Switches: Either ON or OFF

  • Doors: Either OPEN or CLOSED

digital signals

Explain the term Bandwidth, Data Terminal Equipment (DTE), and Data circuit-terminating equipment (DCE).
Bandwidth describes the maximum data transfer rate of a network or Internet connection. It measures how much data can be sent over a specific connection in a given amount of time. For example, a gigabit Ethernet connection has a bandwidth of 1,000 Mbps, (125 megabytes per second). An Internet connection viacable modem may provide 25 Mbps of bandwidth.

While bandwidth is used to describe network speeds, it does not measure how fast bits of data move from one location to another. Since data packets travel over electronic or fiber-optic cables, the speed of each bit transferred is negligible. Instead, bandwidth measures how much data can flow through a specific connection at one time.

When visualizing bandwidth, it may help to think of a network connection as a tube and each bit of data as a grain of sand. If you pour a large amount of sand into a skinny tube, it will take a long time for the sand to flow through it. If you pour the same amount of sand through a wide tube, the sand will finish flowing through the tube much faster. Similarly, a download will finish much faster when you have a high-bandwidth connection rather than a low-bandwidth connection.

Bandwidth also refers to a range of frequencies used to transmit a signal. This type of bandwidth is measured in hertz and is often referenced in signal processing applications.
What is your understanding about the term CODEC and MODEM using suitable example?
COder/DECoder) A hardware circuit that performs analog-to-digital conversion (ADC) and/or digital-to-analog (DAC) conversion. When a digital device receives analog signals from a microphone, VHS tape or other analog source, the ADC converts them to digital audio samples and video frames. Generally, the results are further compressed to save bandwidth
(COmpressor/DECompressor) Software and/or hardware that compresses digital audio and video data in order to reduce file size. Compressed files can be transmitted faster and stored in less space. For example, a song on a CD can be reduced to 10% of its original file size using MP3 compression (see MP3). The size of a movie/video file is dramatically reduced using various compression techniques
Short for modulator-demodulator. A modem is a device orprogram that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form ofanalog waves. A modem converts between these two forms.
Examples of modems include a standard fax/phone modem, a cable modem or a DSL modem or even a satellite modem. All modems perform what is called modulation to encode your data into the line signal and demodulation to decode it from the line signal. The term MODEM is short for Modulator/Demodulator.



Explain the term multiplexer and concentrator with at least one similarity and dissimilarity.
multiplexer - A communications device that multiplexes (combines) several signals for transmission over a single medium. A demultiplexer completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexer and demultiplexer are combined into a single device capable of processing both outgoing and incoming signals. A multiplexer is sometimes called a mux.
concentrator - A type of multiplexor that combines multiple channels onto a single transmission medium in such a way that all the individual channels can be simultaneously active. For example, ISPs use concentrators to combine their dial-up modem connections onto faster T-1 lines that connect to the Internet.

Concentrators are also used in local-area networks (LANs) to combine transmissions from a cluster of nodes. In this case, the concentrator is often called a hub or MAU.

A concentrator is a device which carries multiplexed data packets similar to multiplexer with only difference that it offers storage capability while multiplexer does not
The main difference is in the way input & output relationship is defined. A Mux is hardware device the input & output are directly related to data rate. In concentrator the low speed input channel can share a small no of high speed channel at its output via software control
Explain serial and parallel transmission with suitable diagram
Digital data transmission can occur in two basic modes: serial or parallel. Data within a computer system is transmitted via parallel mode on buses with the width of the parallel bus matched to the word size of the computer system. Data between computer systems is usually transmitted in bit serial mode. Consequently, it is necessary to make a parallel-to-serial conversion at a computer interface when sending data from a computer system into a network and a serial-to-parallel conversion at a computer interface when receiving information from a network. The type of transmission mode used may also depend upon distance and required data rate.
Parallel Transmission

In parallel transmission, multiple bits (usually 8 bits or a byte/character) are sent simultaneously on different channels (wires, frequency channels) within the same cable, or radio path, and synchronized to a clock. Parallel devices have a wider data bus than serial devices and can therefore transfer data in words of one or more bytes at a time. As a result, there is a speedup in parallel transmission bit rate over serial transmission bit rate. However, this speedup is a tradeoff versus cost since multiple wires cost more than a single wire, and as a parallel cable gets longer, the synchronization timing between multiple channels becomes more sensitive to distance. The timing for parallel transmission is provided by a constant clocking signal sent over a separate wire within the parallel cable; thus parallel transmission is considered synchronous.

Serial Transmission

In serial transmission, bits are sent sequentially on the same channel (wire) which reduces costs for wire but also slows the speed of transmission. Also, for serial transmission, some overhead time is needed since bits must be assembled and sent as a unit and then disassembled at the receiver.

Serial transmission can be either synchronous or asynchronous. In synchronous transmission, groups of bits are combined into frames and frames are sent continuously with or without data to be transmitted. In asynchronous transmission, groups of bits are sent as independent units with start/stop flags and no data link synchronization, to allow for arbitrary size gaps between frames. However, start/stop bits maintain physical bit level synchronization once detected.

Explain the term synchronous and asynchronous transmission
The term synchronous is used to describe a continuous and consistent timed transfer of data blocks.

Synchronous data transmission is a data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals.

Synchronous transmission modes are used when large amounts of data must be transferred very quickly from one location to the other

asynchronous transmission works in spurts and must insert a start bit before each data character and a stop bit at its termination to inform the receiver where it begins and ends.

The term asynchronous is used to describe the process where transmitted data is encoded with start and stop bits, specifying the beginning and end of each character.

Explain the term ‘Hub’ and outline at least two major characteristics of it.
This is a hardware device that is used to connect multiple computers together on a network. It is a central connection for all the computers in a network, which is usually Ethernet-based. Information sent to the hub can flow to any other computer on the network. If you need to connect more than two computers together, a hub will allow you to do so.

  • A HUB is a device for connecting multiple ethernet devices together & making them act as single

  • It does not manage any network traffic

  • It is just a BROADCAST device

Explain the term ‘Switch’ and outline at least two major characteristics of it.
A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.

Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.

  • reduces the number of collision domains 

  • connects LAN segments 

  • increases the number of collision domains 

  • filters data before forwarding it to its destination on the network

What is Network Address Translation (NAT) and what is its role in a network?
NAT allows an Internet Protocol (IP) network to maintain public IP addresses separately from private IP addresses. NAT is a popular technology for Internet connection sharing. It is also sometimes used in server load balancing applications on corporate networks.

In it's most common configuration, NAT maps all of the private IP addresses on a home network to the single IP address supplied by an Internet Service Provider (ISP). This allows computers on the home LAN to share a single Internet connection. Additionally, it enhances home network security by limiting the access of external computers into the home IP network space.


  • NAT is a very important aspect of firewall security. It conserves the number of public addresses used within an organization, and it allows for stricter control of access to resources on both sides of the firewall.

  • NAT can be used to allow selective access to the outside of the network, too. Workstations or other computers requiring special access outside the network can be assigned specific external IPs using NAT, allowing them to communicate with computers and applications that require a unique public IP address. Again, the firewall acts as the intermediary, and can control the session in both directions, restricting port access and protocols.

Write two advantages and two disadvantages of ISDN network services.
Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).

There are two types of ISDN:

  • Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one D-channel for transmitting control information.

  • Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe).

ISDN Disadvantages

  • The disadvantage of ISDN lines is that it is very costly than the other typical telephone system.

  • ISDN requires specialized digital devices just like Telephone Company.

ISDN Advantages

ISDN takes only 2 seconds to launch a connection while other modems take 30 to 60 second for establishment.
The basic advantage of ISDN is to facilitate the user with multiple digital channels. These channels can operate concurrently through the same one copper wire pair.
Explain the term ‘Frame relay’, its characteristics, and application with suitable diagram.
Frame relay is a data link network protocol designed to transfer data on Wide Area Networks (WANs). Frame relay works over fiber optic or ISDN lines. The protocol offers low latency and to reduce overhead, does perform any error correction, which is instead handled by other components of the network.

Frame relay has traditionally provided a cost-effective way for telecommunications companies to transmit data over long distances.

Explain your understanding about VoIP and Video over IP?
 VoIP is a technology that allows telephone calls to be made over computer networks like the Internet. VoIP converts analog voice signals into digital data packets and supports real-time, two-way transmission of conversations using Internet Protocol (IP).

VoIP calls can be made on the Internet using a VoIP service provider and standard computer audio systems. Alternatively, some service providers support VoIP through ordinary telephones that use special adapters to connect to a home computer network. 

VoIP offers a substantial cost savings over traditional long distance telephone calls. The main disadvantage of VoIP is a greater potential for dropped calls and degraded voice quality when the underlying network links are under heavy load.

Wired & wireless communication diagram


Wi-Fi wireless fidelity is the technology that allows you to connect to the internet at fast speed without using wires. It allows user to create their own LAN & conduct wireless data transmission between different network elements. Wi-Fi operates at 2.4 Ghz & 5.8 Ghz & each access point can cover about 100 m radius.

WI-Fi Applications:

  • Lab administration

  • People with disabilities

  • Point of care testing

  • Controlling patient data



  • Mobile scanners

  • Direct inventory mgmt.


  • Product Management

  • Field based data collection


  • Mobility

  • Ease of installation

  • Cost

  • Flexibility

  • Speed

  • Roaming

  • Use unlicensed part of radio spectrum


  • Limited range

  • Degradation in performance

  • Interference

Stands for worldwide interoperability for microwave access. The 2 driving forces of modern internet are broadband & wireless. The wimax standard combines the two delivering high speed broadband internet access over wireless connection. Wimax is next generation of wifi or wirless technology that will connect internet at faster speed & much longer ranges than current wirelss tehnology



  • Scalability

  • Quality of service

  • Range

  • Coverage

Benefits of Wi-max

  • Speed: Faster than broadband service

  • Wireless: easier to extend suburban & rural areas

  • Broad coverage: Much wider coverage than Wi-Fi


  • Lack of quality

  • Epxensive network

  • Bad weather

  • Power consuming

Benefits to customers:

VSAT Characteristics & technology

  1. It possesses the ability of digital treatment and transmission for multiple signals including voice, data and television conference. When transmitting voice, data and television conference, data compression technology has been widely adopted.

  2. Flexible multi-access mode. The transmission line from primary station to remote small station is called outbound or outroute while the transmission link from small station to primary station is called inbound or inroute.

  3. Network management system is more and more perfect.

  4. Abundant network topological structure. Network topological structure of VSAT has three kinds which are star-shaped, meshed and composite. Star-shaped structure mainly applied in data communication must have primary station. Meshed structure mainly applied in voice communication doesn’t have primary station. And composite structure with more complex network management and channel control is available for large website comprehensively transferring multiple sets of information. The selection of network topological structure is mainly based on business demand.

  5. Compared with other communication ways, VAST system possess the characteristic that communication link cost is not relevant to the distance, thus it is particularly applied to remote areas.

  6. VSAT system expansion is easier. Use scope and transmission ability of VSAT can be expanded as long as the number of small station is increased and the bandwidth of uplink carrier and downlink carrier is adjusted according to the demand.


What is virtualization? What are its different execution environments? How does it operate over

storage, network, OS servers and application layers? What is cloud computing? Give at least five comparative note of cloud computing with traditional computing?
Network virtualization is a method of combining the available resources in a network by splitting up the available bandwidth into channels, each of which is independent from the others, and each of which can be assigned (or reassigned) to a particular server or device in real time. Each channel is independently secured. Every subscriber has shared access to all the resources on the network from a single computer.

Network management can be a tedious and time-consuming business for a human administrator. Network virtualization is intended to improve productivity, efficiency, and job satisfaction of the administrator by performing many of these tasks automatically, thereby disguising the true complexity of the network. Files, images, programs, and folders can be centrally managed from a single physical site. Storage media such as hard drives and tape drives can be easily added or reassigned. Storage space can be shared or reallocated among the servers.

Network virtualization is intended to optimize network speed, reliability, flexibility, scalability, and security. Network virtualization is said to be especially effective in networks that experience sudden, large, and unforeseen surges in usage.



Packet switching & circuit switching

  • Packet




Category of protocols



Names of protocols

What it does



ethernet, SLIP, PPP, Token Ring, ARCnet

Allows messages to be packaged and sent between physical locations.

Package management(network)



Manages movement of messages and reports errors. It uses message protocols and software to manage this process. (includes routing)

Inter layer communication



Communicates between layers to allow one layer to get information to support another layer. This includes broadcasting

Service control(transport)



Controls the management of service between computers. Based on values in TCP and UDP messages a server knows what service is being requested.

Application and user support



DNS provides address to name translation for locations and network cards. RPC allows remote computer to perform functions on other computers.

Network Management



Enhances network management and increases functionality



FTP, TFTP, SMTP, Telnet, NFS, ping, Rlogin

Provides direct services to the user.

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