What are the five important components of data communication? List two advantages of layering principle in computer networks. With the example explain half duplex communication. Mention any two functions of session layer. Name four topologies of computer networks. Suggest two points to improve the performance of network.
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What is mean by data communication? Data communication is the exchange of data in the form of 1s and 0s between two devices via some form of transmission medium such as a wire cable. What are the three criteria necessary for an effective and efficient network? The most important criteria are performance, reliability and security. Security issues include protecting data from unauthorized access and viruses.
What are the three fundamental characteristics determine the effectiveness of the data communication system? The effectiveness of the data communication system depends on three fundamental characteristics: Delivery: The system must deliver data to the correct destination. Accuracy: The system must deliver data accurately. Timeliness: The system must deliver data in a timely manner. What are the advantages of distributed processing?
Why are protocols needed? In networks, communication occurs between the entities in different systems. Two entities cannot just send bit streams to each other and expect to be understood.
For communication, the entities must agree on a protocol. A protocol is a set of rules that govern data communication 6. Why are standards needed? Co-ordination across the nodes of a network is necessary for an efficient communication. If there are no standards, difficulties arise. A standard provides a model or basis for development to which everyone has agreed. What is the difference between a passive and an active hub? An active hub contains a repeater that regenerates the received bit patterns before sending them out.
A passive hub provides a simple physical connection between the attached devices. Distinguish between peer-to-peer relationship and a primary-secondary relationship.
P e e r -t o-peer relationship: All the devices share the link equally. P r i m ary-secondary relationship: One device controls traffic and the others must transmit through it. Raghavendra Reddy Malapati Page 2 9. Group the OSI layers by function. The seven layers of the OSI model belonging to three subgroups. Physical, data link and network layers are the network support layers; they deal with the physical aspects of moving data from one device to another.
Session, presentation and application layers are the user support layers; they allow interoperability among unrelated software systems.
The transport layer ensures end-to-end reliable data transmission. What are header and trailers and how do they get added and removed? Each layer in the sending machine adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it.
This information is added in the form of headers or trailers. Headers are added to the message at the layers 6,5,4,3, and 2. A trailer is added at layer2.
At the receiving machine, the headers or trailers attached to the data unit at the corresponding sending layers are removed, and actions appropriate to that layer are taken. The transport layer creates a communication between the source and destination. What are the three events involved in a connection? Creating a connection involves three steps: connection establishment, data transfer and connection release.
In the NRZ-L sequence, positive and negative voltages have specific meanings: positive for 0 and negative for 1.
Instead, the receiver looks for changes from one level to another as its basis for recognition of 1s. What are the functions of a DTE? What are the functions of a DCE? Data terminal equipment is a device that is an information source or an information sink. It is connected to a network through a DCE. Data circuit-terminating equipment is a device used as an interface between a DTE and a network. What does the electrical specification of EIA describe?
The data must be transmitted using NRZ-L encoding. Discuss the mode for propagating light along optical channels There are two modes for propagating light along optical channels, multimode and single mode. M u ltimode: Multiple beams from a light source move through the core in different paths. Single mode: Fiber with extremely small diameter that limits beams to a few angles, resulting in an almost horizontal beam. What is refraction? The phenomenon related to the bending of light when it passes from one medium to another.
Raghavendra Reddy Malapati Page 3 What are the disadvantages of optical fiber as a transmission medium? What are the criteria used to evaluate transmission medium? Explain cross talk and what is needed to reduce it? Effect of one wire on another is called as cross talk. One wire will be the sending antenna and the other wire will be the receiving antenna. We can use the shielded twisted pair cable or coaxial cable for transmission, which contains metal foil to reduce cross talk.
What are the responsibilities of data link layer? Specific responsibilities of data link layer include the following.
Mention the types of errorsE There are 2 types of errors a Single-bit error. Define the following terms. What is redundancy? It is the error detecting mechanism, which means a shorter group of bits or extra bits may be appended at the destination of each unit.
List out the available detection methods. There are 4 types of redundancy checks are used in data communication. Write short notes on VRC. The most common and least expensive mechanism for error detection is the vertical redundancy check VRC often called a parity check. Write short notes on LRC. In longitudinal redundancy check LRC , a block of bits is divided into rows and a redundant row of bits is added to the whole block.
Write short notes on CRC. The third and most powerful of the redundancy checking techniques is the cyclic redundancy checks CRC CRC is based on binary division. Here a sequence of redundant bits, called the CRC remainder is appended to the end of data unit.
Write short notes on CRC generator. A CRC generator uses a modulo-2 division. Write short notes on CRC checker. A CRC checker functions exactly like a generator. After receiving the data appended with the CRC it does the same modulo-2 division. Otherwise, the received stream of bits is discarded and the dates are resent.
What are the steps followed in checksum generator? The sender follows these steps a The units are divided into k sections each of n bits. List out the steps followed is checksum checker side. The receiver must follow these steps a The unit is divided into k section each of n bits.
Write short notes on error correction. It is the mechanism to correct the errors and it can be handled in 2 ways.
What is the purpose of hamming code? A hamming code can be designed to correct burst errors of certain lengths. So the simple strategy used by the hamming code to correct single bit errors must be redesigned to be applicable for multiple bit correction. Define flow control. Flow control refers to a set of procedures used to restrict the amount of data. The sender can send before waiting for acknowledgment.
What is a buffer? Each receiving device has a block of memory called a buffer, reserved for storing incoming data until they are processed. Mention the categories of flow control. There are 2 methods have been developed to control flow of data across communication links. Mention the function of go-back N-ARQ.
EC2352 Computer networks May/june 2016 Reg 2008