Unit2[1]
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basics of computers

basics of computers

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Unit2[1] Document Transcript

  • 1. Applications of Networking 1. Resource Access Regardless of the physical location of the resources and the users, networks can provide special computing resources with convenient access at any time to its users. These resources sharing may be of specialized computers, software or other devices that are expensive or unique. For example accessing a corporate supercomputer from workstations at remote research laboratories. 2. Data Access Networks can provide access to unique database to its local and remote users. 3. Communication and Data Exchange Networks allow users to exchange data, graphs or documents and to communicate using email, bulletin boards or by teleconference, irrespective of the time or their location. 4. Decentralization of Data Processing A complicated job can be divided into multiple modules and can be distributed to different departments for processing. 5. Easy Communication Various organizations cooperating in a task can communicate with each other on network and exchange information. Internet Security As internet is open to all, the security, privacy, authenticity and anonymity issues play a vital role as one need to be sure about these things, then only he can use the Internet to its fullest extent. As information and its transfer are crucial for every one who is using the internet, there need to be provisions, which is reliable then only one can connect to internet. The security of internet can be divided into two broad categories, namely:
  • 2. 1. Client-Server Security 2. Data & Transaction Security Client-Server Security This security is for preventing unauthorized access to restricted databases and other information which is confidential. This is an authorization mechanism, which makes it sure that the users, who are authorized only should be able to connect and access the information. These mechanisms are required to ensure that only authenticated users can access the resources, which they are entitled to. Password protection, encrypted smart cards, biometrics, firewalls etc. are some of the methods adopted to ensure client- server security. Data & Transaction Security As the data transmissions and transactions occur across the network, there are fair chances that they can be intercepted, read and manipulated as well as the source and destination can be tracked. To prevent this one has to provide security to the data and transactions, which is usually done by using data encryptions, which is implemented through various cryptographic methods. Security Methods for Client/Server & Data/Transaction Security 1. Password Scheme: This is an easy solution to provide security, so that unauthorized users do not get access to the data. This is the first level of security, which can be provided. Here, the authorized users are assigned user names and a password is associated to them, which are to provided when connecting to the site. But this security measure can be broken easily, if common words or proper names are used as passwords, but if alphanumeric passwords of bigger length are used, then it is very difficult to break them. Another problem is that, if the login is remote, then the password travels through the system to server for authentication, in meantime, it can be trapped, for this reason the passwords are to be encrypted before transmitting them. But in spite of these threats, password schemes are still the most popular forms of ensuring security.
  • 3. 2. Firewalls Firewall is accepted as the network protection mechanism, it is a barrier between corporate network and the outside world, which will ensure that the authentic users only connect as well only the data which is harmless enters and leaves the system. The term firewall can be defined as a device, a computer or a router which is placed between the network and the internet to control and monitor the traffic between the inside and outside world. Firewall is a device which is used to shield vulnerable areas from various dangers. The firewall system is located at a gateway point which actually is the connecting point to the outside world. Firewalls come in many varieties and offer different features, but the basic feature is to filter the traffic of data and control it. 3. Encryption This method of data and transaction security is used for retaining confidentiality and integrity of the data being transmitted. Data confidentiality is that property, which makes data contents to be safe from being read, while on the path of transmission, which is made sure by using cryptography algorithms for encrypting data, which no one can interpret. Along with data being confidential, it has to remain unmodified, while on transit i.e. the data should be intact without any modifications, while it is on way to destination. This is made sure by using various encryption techniques like Secret-Key Cryptography, Data Encryption Standard(DES), Public Key Cryptography RSA etc. Analog Signals Analog signals are continuous in nature, they carry information in the form of waves e.g., the way sound travels in the medium such as telephone lines. Analog communication uses general purpose communication channels. These signals are characterized by two parameters such as amplitude and frequency. Digital Signals Digital signals are discrete in nature. They transfer information in the form of 0s and 1s. in digital communication, data are transmitted directly in binary form that is a sequence of 0s and 1s. to transmit binary data over these channels 0s and 1s should be converted to the electrical signals. This is done by Modem (modulator-demodulator). Digital signals are preferred over analog signals. Because of the
  • 4. discrete nature, these signals are not affected by noise or any other disturbances. Moreover, computer at the receiving end does not perform any conversion as in analog signals i.e. analog to digital. Packet Transmission: • Computers use data grouped into packets for transmission • Local Area Networks • Wide Area Networks • Addressing and Routing Concepts of Packets: • Computer networks divide data into small blocks called packets • Packets are send individually • Often called packet networks and packet switching networks • Motivation for using packets o Sender and receiver needs to coordinate transmission to ensure that data arrives correctly o Helps determine which blocks arrive intact and which do not o Computers often share underlying connections and hardware o Packet switching helps ensure fairness to access Shared Resources: 1. The first networks 1.1. A 5 MB file at 56 Kbps will take 12 min to transfer from A to D 1.2. B & C must wait 2. Packet networks 2.1. Divide data into packets of 1000 bytes each 2.2. A sends a packet to D taking only 143 ms 2.3. B transmits data to C 2.4. A continues 3. No long delays
  • 5. Packets and TDM 1) Time Division Multiplexing a) Many resources take turns accessing the shared communication resources 2) All sources receive prompt service 3) The source with less Packets and Frames 1. Packet refers to a small block of data 2. Each hardware technology uses different packet format 3. Frame denotes packet used with specific type of network 4. EX : RS-232 mechanism 4.1. Does not include a mechanism that allows a sender to signal the end of a block of characters 4.2. Sending and receiving computers must agree on such details 5. Network systems can choose two unused values to define format 6. EX: RS-232 can use frame delimiters 6.1. Soh –start of header 6.2. Eot – end of transmission 7. Overhead is an disadvantage 7.1. An extra, unnecessary character between blocks of data 8. Advantageous when large delays or computer crashes 8.1. Missing eot indicates sending computer crashed 8.2. Missing soh indicates receiver missed beginning of frame
  • 6. Packet transmission: A packet transmission rate control scheme between nodes on a wireless Ad-hoc network is proposed considering the characteristics of Wireless LAN rent transmission efficiencies by different transmission distances. Many energy efficient routing algorithms researches have been conducted only on the assumption of ideal experimental cases. This paper considers the way of finding suitable transmission rate for the transmission distances between nodes on a mobile Ad-hoc networks so that a more realizable method is presented. In this research, a controlling algorithm for transmission data rates by the distances between mobile nodes is realized using Fuzzy logic, possibly available to be applied to Ad- hoc network routing, and simulations are conducted to verify the enhancements in throughput. Long distance communication: method of forming a long distance communication channel between two telephone devices each of which are connected to a PSTN, said method comprising a user of one of said telephone devices initiating and establishing a telephone communication with a first commercial access provider node of INTERNET and providing thereto a telephone address, using INTERNET to establish a communication channel between said first commercial access provider node and a second commercial access provider node of INTERNET and providing said telephone address to said second commercial access provider node, said second commercial access provider node using said telephone address and a telephone dial out capability of said second commercial access provider node to establish a communication with a telephone device at the telephone address using a PSTN, and using the INTERNET communication channel to link said telephone devices and form a real time voice communication between said telephone devices. 2. A method as claimed in claim 1 including, after initiating said telephone communication with said first commercial access provider node, said first commercial access provider node communicates with said user to establish authorization for completing a long distance communication. 3. A method as claimed in claim 1 wherein said first and second commercial access provider nodes encrypt signals there between and decrypt received signals such that signals transmitted over INTERNET are encrypted.
  • 7. 4. A method as claimed in claim 1 wherein said telephone devices are conventional telephones. 5. A method as claimed in claim 4 wherein signals transmitted between said commercial access nodes using INTERNET are encrypted. 6. A method as claimed in claim 1 wherein the originating telephone device has a predetermined arrangement with said first commercial access provider node and said second telephone device has no prior relationship with either of said commercial access provider nodes. 7. A method as claimed in claim 5 wherein each commercial access node has different DID telephone addresses for voice and facsimile transmissions. 8. A method of establishing a long distance telephone communication between an initiating telephone device and a receiving device telephone identified by a telephone address, said method comprising using a PSTN to initiate a telephone communication with a commercial access provider node of a digitized packet based network and provide the node with said telephone address, said commercial access provider node causing a real time voice communication channel to be formed between said telephone devices, which communication channel includes an initial PSTN segment between the initiating telephone device and said commercial access provider node a digitized packet based network segment between said commercial access provider node, and a further commercial access provider node and a PSTN segment between said further commercial access provider node and the telephone device identified by the telephone address, wherein the further commercial access provider node uses the telephone address and the PSTN to initiate the PSTN segment there between. 9. A method as claimed in claim 8 wherein said telephone devices are conventional telephones. 10. A method of forming a long distance telephone communication between a first telephone device and a second telephone device which communication is capable of transmitting real time voice communications similar to existing long distance voice telephone communications, comprising the steps of forming an initial telephone link between the first telephone device and a commercial access provider node of a digitized packet based network and providing thereto a telephone address of the second telephone device, said commercial access provider forming an appropriate digitized packet based communication channel with a further commercial access provider node located in closer proximity to the location of the second telephone device
  • 8. and providing thereto said telephone address, said further commercial access provider establishing a telephone link with said second telephone device using said telephone address, and then linking said telephone devices using said digitized packet based communication channel thereby forming a real time voice communication between said telephone devices. 11. A method as claimed in claim 10 wherein said second telephone device requires no prearrangement with said further commercial access provider node. 12. A communication arrangement for long distance telephone to telephone voice communication comprising a first provider node of a digitized packet based network having means to allow users to initiate a telephone communication with a desired telephone device identified by a telephone address by the steps of initially forming a communication with said first provider node and providing said telephone address thereto, said first provider node cooperating with a second provider node of said digitized packet network to form a real time voice communication channel there between and said second provider node including dial out capabilities which are used upon receipt of the telephone address provided thereto to form a telephone communication with the telephone device, said second provider cooperating with said first provider node to link the telephone devices using a digitized packet based network segment between said provider nodes and using PSTN segments between the initiating telephone device and the first provider node and between the second commercial access provider node and said telephone device identified by said telephone address, wherein the first and second provider nodes appropriately process the signals for transmission using the digitized packet based network. 13. A communication arrangement as claimed in claim 12 wherein the signals transmitted over the digitized packet based network are encrypted by said commercial access provider nodes. 14. A long distance telephone communication arrangement having three distinct communication segments, comprising a first communication segment which carries voice communication over a PSTN between a first telephone device and a first commercial access provider node of a digitized racket based network a second segment between said first commercial access provider node and a second commercial access provider node of said digitized packet based network which exchange digitized voice packets there between based on communications received from the first and third segments, said third segment carrying voice communication over a PSTN
  • 9. between a second telephone device and said second commercial access provider node after said second commercial access provider node has established said third segment with said second telephone device, and wherein said second commercial access provider establishes said third segment with said second telephone device by using the telephone address of said second telephone device provided thereto by said first provider which received the telephone address in a communication from said first telephone device. 15. A long distance telephone communication arrangement as claimed in claim 14 wherein said first and second commercial access provider nodes carry out all necessary signal conversion to and from the first and third segments. 16. A long distance telephone communication arrangement as claimed in claim 14 wherein said first and second commercial access provider nodes encrypt signals transmitted on the second segment. 17. A long distance telephone communication arrangement as claimed in claim 14 wherein said first and second commercial access provider nodes convert the signals for transmission by the second segment to a different form relative to the signals carried by the first and third segments. 18. A long distance telephone communication arrangement having three distinct communication segments for transmitting a signal, comprising a first communication segment which carries voice communication over a PSTN between a first telephone device and a first commercial access provider of a digitized packet based network, a second segment between said first commercial access provider and a second commercial access provider of said digitized packet based network which exchange digitized voice packets there between based on communications received thereby, and a third segment which carries voice communication over a PSTN between a second telephone device and said second commercial access provider and wherein said first and second commercial access providers convert the signal to and from the first and third segments whereby the signal carried by the second segment is in a form different from the signal carried by at least one of the first and third segments, and wherein said second commercial access provider establishes said third segment with said second telephone device by using the telephone address of said second telephone device provided thereto by said first provider which received the telephone address in a communication from said first telephone device. 19. A long distance telephone communication arrangement comprising a digitized packet based network segment between at least two commercial access providers of the digitized packet based network, said commercial access providers cooperating to form a communication channel having a real
  • 10. time digitized packet based communication segment, said communication channel linking a first telephone device and a second telephone device, said communication channel being established upon receipt of an initial telephone communication with one of said commercial access providers from said first telephone device which communication includes a telephone address of the second telephone device, and where after said telephone address is transmitted over the digitized packet based network to the other commercial access provider which uses the same to form a telephone communication with said second telephone device identified by the telephone address, and thereafter said telephone devices are connected using the digitized packet based segment.