Download question answer unit 1 and more Lecture notes Data Communication Systems and Computer Networks in PDF only on Docsity!
Subject : Data Communication (5KS01)
Important Questions with Answers
Unit 1
Que 1]
Ans :
What is network? Explain the important criteria that are necessary to make the network effective and efficient. (S-2017 for 7 M, W -2016 for 7 M, W-2015 for 7 M, S-2014 for 7 M)
Network is a set of devices (often referred to as nodes) connected by media link node can be a computer, printer, or any other device capable of sending and/or receiv- ing data generated by other nodes on the network. The links connecting the devices are often called communication channels. Network Criteria A network can be effective and efficient, if a network meets the following different criteria. The important criteria are performance, reliability and security as shown in following figure.
Figure: Network Criteria
i) Performance
Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another device. Response time is the elapsed time between an inquiry and a response. The performance of a network depends on following factors.
a) Number of users : Large no. of concurrent response time in a network, as they are not designed to handle heavy traffic loads. The design of a given network is based on an evaluation of the average number of that will be communicating at any one time. In peak load periods, yet, the actual number of users can exceed the average and thereby decrease performance.
b) Type of transmission medium
The medium defines the speed at which data can travel through a connection. Networks are moving faster and faster through transmission media such as fiber-optic cabling. A medium that can carry data at 100 megabits per second is 10 times more powerful than can carry data at only 10 megabits per second.
c) Hardware
The types of hardware included in a network affect both the speed and capacity of transmission. A higher-speed computer with greater storage capacity provides better performance.
d) Software
The software used to process data at the sender, receiver, and intermediate nodes also affects the network performance. Moving a message from node to node through a network requires processing to the raw data into transmittable signals, to route these signals to the proper destination, to ensure error-free delivery, and to recast-the signals into a form the receiver can use. The software that provides these services affects both the speed and the reliability of a Well-designed software can speed the process and make transmission more effective and efficient.
Ans:
A signal has a bit rate has 2000 bps. What is the duration of each bit? If the digital signal has a bit interval of 40 microseconds, what is the bit rate? (W -2016 for 6 M, W -2012 for 7 M) Bit interval and Bit rate Most digital signals are aperiodic and, thus, period or frequency is not appropriate. Two terms, bit interval (instead of period) and bit rate (instead of frequency) are used to describe digital signal.
- The bit interval is the time required to send one single bit.
- The bit rate is number of bit intervals per second. This means that the bit rate is the number of bits sent in one second and expressed in bits per second (bps) as shown in figure.
Figure : Bit interval and Bit rate
A signal has a bit rate has 2000 bps. What is the duration of each bit? Solution: The bit interval is the inverse of the bit rate. Bit interval = 1/(bit rate) = 1/2000 = 0.00050 second = 500 × 10 -6^ Seconds
= 500 μs If the digital signal has a bit interval of 40 microseconds, what is the bit rate? Solution: The bit rate is the inverse of the bit interval Bit rate = 1/(bit interval) = 1/(40 × 10 -6^ ) = 25,000 bits per seconds
= 25 × 10 3 bits per seconds = 25 Kbps
Que 3]
Ans:
Distinguish between peer to peer relationship and primary secondary along with example. (S-2017 for 6 M, W-2014 for 7 M, S-2103 for 7 M) Topology The term topology refers to the way a network is laid out, either physically or logically. Two or more devices connect to a link; two or more links form a topology of a network is the geometric representation of the relationship of all the of a network is the geometric representation of the relationship of all the linking devices (usually called nodes) to each other. There are five basic topologies possible: mesh, star, tree, bus, and ring shown in figure.
Figure: Fully connected mesh topology (for five devices)
Advantages
- The use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems that can occur when links must be shared by multiple devices.
- A mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system.
- There is the advantage of privacy or security. When every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages.
- Point-to-point links make fault identification and fault isolation easy. Disadvantages
- The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required because every device must be connected to every other device, installation and reconnection are difficult.
- The sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate.
- The hardware required to connect each link (I/O ports and cable) can be prohibitively expensive.
2) Star
In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub. The devices are not directly linked to one another. Unlike a mesh topology, a star topology does not allow direct traffic between devices. The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device.
Figure: Star topology
Advantages
- A star topology is less expensive than a mesh topology. In a star, each device needs only one link and one I/O port to connect it to any number of others.
- It easy to install and reconfigure. Far less cabling needs to be housed, and additions, moves, and deletions involve only one connection: between that device and the hub.
Figure: Tree topology
Advantages
- It is less expensive than mesh topology.
- Easy to install and reconfigure.
- Easy for fault identification and fault isolation.
- It is robust.
- It allows more devices to be attached to a single central hub and can therefore increase the distance a signal can travel between devices.
- It allows the network to isolate and priorities communication from different computers.
Disadvantages
- A tree requires less cable each node must be linked to a central hub. For these reason more cabling is required in a tree than in some other topologies.
4) Bus
A bus topology is a multipoint in which one long cable acts as a backbone to link all the devices in the network. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. As a signal travels along the backbone, some of its energy is transformed into heat. Therefore, it becomes weaker and weaker as it travels farther and farther. For this reason there is a limit on the number of taps a bus can support and on the distance between those taps.
Figure: Bus topology
Advantages
- It is simple for installation.
Figure: Ring topology
Advantages
- A ring is relatively easy to install and reconfigure. Each device is linked to only its immediate neighbors (either physically or logically). To add or delete a device requires changing only two connections.
- (^) Fault isolation is simplified. Generally in a ring, a signal is circulating at all times. If one device does not receive a signal within a specified period, it can issue an alarm. The alarm alerts the network operator to the problem and its location. Disadvantages
- Numbers of devices connected are restricted due to traffic considerations.
- Unidirectional traffic.
- A break in the ring (such as a disabled station) can disable the entire network. This weakness can be solved by using a dual ring or a switch capable of closing off the break.
6) Hybrid A network combines several topologies as subnetworks linked together in a larger topology. For example, one department has decided to use a bus topology while another department has a ring. The two can be connected to each other via a central controller in a star topology as shown in figure.
Figure: Hybrid topology
Que 4]
Ans:
State and explain various types of transmission modes with example. (W -2014 for 7 M, W -2013 for 7 M, W -2012 for 7 M) The term transmission mode is used to define the direction of signal flow between two link devices.
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 as shown in figure. The half duplex mode is link a one lane road with two directional traffic. While cars are travelling one direction, cars going the other way must wait. In a half duplex transmission, the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time.
Figure: Half – duplex Walkie – talkies and CB (citizen’s band) radios are both half duplex systems.
3) Full – duplex
In full duplex mode (also called duplex), both station can transmit and receive simultaneously as shown in figure. The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time. In full-duplex mode, signals going in either direction share the capacity of the link. This sharing can occur in two ways: either the link must contain two physically separate transmission paths, one for sending and the other for receiving, or the capacity of the channel is divided between signals traveling in opposite directions.
Figure: Full duplex One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time.
Que 5]
Ans:
If a periodic signal is decomposed into five sine wave with frequencies of 100, 300, 500, 700 and 900 Hz, what is the bandwidth? Draw the spectrum assuming all components have maximum amplitude of 20 volts. (S -2015 for 7 M) Given data, f (^) h be the highest frequency = 900 KHz f (^) l be the lowest frequency = 100 KHz
To find B, Bandwidth =? Bandwidth (B) = f (^) h - f (^) l = 900 – 100 = 800 KHz
The spectrum has five bars, at 100, 300, 500, 700 and 900 Hz as shown in following figure.
