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Computer Network Old Question Solution COMPUTER NETWORK OLD QUESTION SOLUTION 2069 CHAITRA 1. Explain the need of Networking Software in the form of Hierarchy. Mention in which level layer of OSI reference model following tasks are done. [6+2] (i) Timing and voltage of received signal (ii) Encryption and decryption of data (ii) Data framing (i) Point-to-point connection of socket. Ans.: Networking software is a foundation element for any network which helps network administrators deploy, manage, and monitor a network. Networking software is invisible to end-users- it is simply used to facilitate the access those users have to network resources, in a seamless way. It allows multiple devices, such as desktops, laptops, mobile phones, tablets, and other systems to connect to one another, as well as other networks. The internet is a prime example of a globally connected system of servers and computers that relies on networking software to ensure accessibility by end users. The first computer networks were designed with hardware as the main concern and the software as an afterthought. This strategy no longer works due to the advent of software revolution. To reduce the design complexity, most networks are organized as a series or hierarchy of layers or levels. The numbers of layers, the name of each layer, the contents of each layer and the function of each layer differ from network to network. Layer n on one machine communicates with the layer n on another machine on the network using some rules known as the layer n protocol. A protocol is an agreement between the communicating parties on how the communication is to proceed. The entities comprising the corresponding layers on two communicating machines over the network are called peers. In reality, no data is transferred from layer n on any two machines. Instead, each data and control information is passed to the layer below. Additional information including protocol control information may be appended by each layer to data as it travels from higher to lower layers in the form of layer headers. Below layer 1 is the physical medium through which actual communication occurs over communication channels. Network Software is needed to ease the transaction of data through the different hierarchy of protocols between these different layers efficiently. The level layer in which the given tasks are performed are mentioned below: 1. Timing and voltage of received signal: Physical Layer 2. Encryption and Decryption of data: Presentation Layer 3. Data framing: Data Link Layer 4. Point-to-point connection of socket: Transport Layer 2. Define switching and multiplexing. Differentiate between circuit switching and packet switching. [4+4] Ans.: Switching is the process that implies that we can dynamically configure a network which is less than fully connected in order to join any two nodes for communication. It is the most valuable asset of computer networking. Every time in computer network, a user access the internet or another computer network outside the user’s immediate location, the message requests are sent through a maze of transmission media and connection devices. Simply, switching is the mechanism for exchange of information between different computer networks and network segments. There are basically three types of switching methods available: 2. Circuit Switching Circuit Switching maintains the idea of dedicated connections between two endpoints, but allows for sharing of channels within the network, and hence is much more scalable. Circuit switching takes advantage of the fact that while everybody needs t be able to talk to everybody else, the aren’t likely to all do so at the same time. The telephone network is based on circuit switching. 3. Message Switching Message switching does not set up a dedicated channel (or circuit) between the sender and recipient during the communication session. In message switching each message is treated as an independent block. In this type of networking, each message is then transmitted from first network device to second network device through the internetwork i.e. message is transmitted from the sender to intermediator device. 4. Package Switching Package switching alleviates the problems of circuit and message switching. A small upper bound is put on the maximum size of a packet sent through the network. No reserved channel is created ahead of time, each packet belonging to a single message may take a different route through the network. Since there is no reservation of capacity it is possible that congestion becomes a problem. Too many packets trying to get through the same router requires that the router be able to buffer packets. All buffers have finite size, so it is possible that packets are dropped. Multiplexing is the method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource. In telecommunication, several telephone calls may be carried using one wire. Long distance links use high capacity point-to-point connections with a single physical medium. Some means must be found for the sharing the capacity to enable multiple simultaneous uses of the medium. The motivation is the same here as for time shared operating systems. There are three wars to divide a channel: 3. Frequency Division Multiplexing Frequency Division Multiplexing (FDM) is possible when a single source requires less than the total available bandwidth in the medium. Frequency modulation lets data be moved to any particular part of the frequency spectrum of the channel. Multiple sources can thus share the same medium, by using different parts of the channel simultaneously. FDM allows for full duplex modems, radio, and TV. 4. Time Division Multiplexing If the data rate of a medium is larger than the data rate (bps) of a source channel, then multiple channels can be sent by allotting different channels different slices of time. The multiple channels can be interleaved by bit, byte or frame. There are two types of TDM: Synchronous TDM and Asynchronous TDM. The issues of link control are handles per channel, independent of the TDM. 5. Code Division Multiplexing Code Division Multiplexing (CDM) is a class of techniques here several channels simultaneously share the same frequency spectrum, and this spectral bandwidth is much higher than the bit rate or symbol rate. One form is frequency hopping, another is direct sequence spread spectrum. In the latter case, each channel transmits its bits as a coded channel-specific sequence of pulses called chips. Number of chips per bit, or chips per symbol is the spreading factor. This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber or radio channel or other medium, and asynchronously demultiplexed. The differences between Circuit switching and packet switching are given below: Circuit Switching Packet Switching It is connection oriented. It is connectionless oriented. It was initially designed for voice It was initially designed for data communication. transmission. It is inflexible because once a path is set all It is flexible because a route is created for parts of a transmission follows the same each packet to travel to the destination. path. The message is received in the order it The packets of a message is received out was of sent from the source. order and must be assembled at the destination. Circuit switching can be achieved using two Packet switching has two approaches- technologies, either Space division switching Datagram approach and Virtual Circuit or Time-Division Switching. Approach. Circuit switching is implemented at Packet switching is implemented at physical Network layer. Layer. 3. Explain the different types of Data link layer framing mechanisms. [8] Ans.: Frames are the units of digital transmission particularly in computer networks and telecommunications. Frames are comparable to packets of energy called photons in case of light energy. Frame is continuously used in Time Division Multiplexing process. Framing is a point-to-point connection between two computers or devices consisting of a wire in which data is transmitted as a stream of bits. However, these bits must be framed into discernible blocks of information. Framing is a function of the data link layer. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. Ethernet, token ring, frame relay, and other data link layer technologies have their own frame structures. Frames have headers that contain information such as error- checking codes. A frame has the following parts: Frame Header: It contains the source and destination addresses of the frame. Payload Field: It contains the message to be delivered. Trailer: It contains the error detection and error correction bits. Flag: It marks the beginning and end of the frame. There are two types of framing techniques: 1. Fixed Size: The frame is of fixed size and there is no need to provide boundaries to the frame, length of the frame itself acts as delimiter. Frames can be of fixed or variable size. In fixed-size framing, there is no need for defining the boundaries of the frames; the size itself can be used as a delimiter. An example of this type of framing is the ATM wide-area network, which uses frames of fixed size called cells. 2. Variable Size: In this there is need to define end of frame as well as beginning of next frame to distinguish. In variable-size framing, we need a way to define the end of the frame and the beginning of the next. Historically, two approaches were used for this purpose: a character-oriented approach and a bit-oriented approach. The defining of end and beginning of the frame can be done in two ways: 1.
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