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PRESENTATION COMPUTER NETWORKS

PRESENTATION COMPUTER NETWORKS. UNIT 2: PHYSICAL LAYER. CONTENTS. Transmission Media Switching ISDN and its Service Multiplexing Modems. TRANSMISSION MEDIA. Sending of data from one device to another is called transmission of data.

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PRESENTATION COMPUTER NETWORKS

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  1. PRESENTATIONCOMPUTER NETWORKS

  2. UNIT 2: PHYSICAL LAYER

  3. CONTENTS • Transmission Media • Switching • ISDN and its Service • Multiplexing • Modems

  4. TRANSMISSION MEDIA • Sending of data from one device to another is called transmission of data. • Transmission of data through Medium is called Transmission Media. • Transmission media refers to wires, cables by which data travels from source to destination. • Transmission media refers to the channels that describes the data path for communication among sender and receiver. (To be continued)

  5. TYPES OF TRANSMISSION MEDIA • Guided (Wired) • Twisted Pair • Coaxial Cable • Fibre Optics • Unguided (Wireless) • Wi-Fi • Bluetooth • Infrared (To be continued)

  6. GUIDED MEDIA:Guided media is of 3 types:- TWISTED PAIR: it consists of two bunches of thin copper wire each bunch enclosed in a plastic insulation and then twisted around each other to reduce interference. Twisted pair is limited in distance, bandwidth and data rate. Twisted pair controls “crosstalk”. Twisted pair cable is connected by a special connector called RJ-45. Twisted pair has high attenuation. Maximum length of cable is 100m. (To be continued)

  7. CATEGORIES OF TWISTED PAIR CABLES • Cat 1 • Mostly used in telephone systems. • Suitable for voice only. • Cat 2 • Support data transmission speed of upto 4mbps. • Cat 3 • Support data transmission speed upto 10 mbps • Cat 4 • Support data transmission speed upto 16 mbps • Cat 5 • Support data transmission speed upto 100 mbps. • Mostly used grade of cable in networking. (To be continued)

  8. COAXIAL CABLE:Coaxial cable consist the followings layers in its construction: - Core - Thick insulated sheet - Copper Mesh - Protective plastic covering Coaxial Cable is a group of specially wrapped insulated wire lines which are able to transmit data at high rates. Coaxial Cable is joined by a special connector known as BNC connector. It has low attenuation. Coaxial cable can be used over longer distances and support more stations on a shared line than twisted pair. (To be continued)

  9. TYPES OF COAXIAL CABLES Types of coaxial cable used in networking • 50 ohm RG8,RG11 • 50 ohm RG58 • 75ohm RG59 • 93ohm RG63 Ohm means unit of Resistance RG means Govt Rating. (To be continued)

  10. FIBRE OPTICS: • Fibre optic cable is known as most sophisticated cables used in long distance network connection. • Through this cable data transmission is done through « Light ray signal  transmission» rather than electrical signal transmission. • It has inner core of glass that conducts light. This inner core is surrounded by cladding. • Cladding is nothing but layer of glass material that reflects light back into the core. • Each fiber is then surrounded by plastic covering. (To be continued)

  11. TYPES OF FIBER OPTICS • Plastic core and cladding : Beneficial over glass fibres. Plastic fibres are more elastic. They are used in single building or complex. • Glass core with plastic cladding: Also known as PCS(Plastic clad silica). Has low attenuation. Mostly used in military applications. • Glass core and glass cladding: Also known as SCS (Silica clad silica). (To be continued)

  12. UNGUIDED MEDIA:Unguided media is of 3 types:- Wi-Fi: • Wi-Fi stands for Wireless Fidelity. • Basic concept is same as Walkie talkies. • A Wi-Fi hotspot is created by installing an access point to an internet connection. • An access point acts as a base station. • When Wi-Fi enabled device encounters a hotspot the device can then connect to that network wirelessly. • A single access point can support up to 30 users and can function within a range of 100 – 150 feet indoors and up to 300 feet outdoors. • Many access points can be connected to each other via Ethernet cables to create a single large network. (To be continued)

  13. BLUETOOTH: “Bluetooth is a low-cost, low power, short range wireless communication technology used in networking, mobile phones and other portable device. Bluetooth wireless technology also enables devices to communicate with each other as soon as-they come within range; no need to connect, plug into, install, enable or configure anything.” (To be continued)

  14. INFRARED: “Infrared technology allows computing devices to communicate via short-range wireless signals. With infrared, computers can transfer files and other digital data bidirectionally. The infrared transmission technology used in computers is similar to that used in consumer product remote control units.” Range - Infrared communications span very short distances. Place two infrared devices within a few feet (no more than 5 meters) of each other when networking them. Unlike Wi-Fi and Bluetooth technologies, infrared network signal cannot penetrate walls or other obstructions and work only in the direct "line of sight.“

  15. INFRARED

  16. SWITCHING

  17. SWITCHING • Switching is a mechanism which is used to switch between the sender and the receiver. • A switched network consists of series interlinked nodes called switches. • Switches are hardware devices which are capable of creating a connection between two or more devices connected to the switch but to each other. • There are 3 different methods of establishing a connection between the sender and receiver. - Circuit Switching - Message Switching - Packet Switching

  18. CIRCUIT SWITCHING • It is the simplest method of data communication in which a dedicated physical path is established between the sending and the receiving station through the nodes of the network. • In this method, transmission lines are open between two parties and held open until their communication is finished. • Data is transmitted without any delay once connection is established. • The time of possible congestion is only at the startup time. (To be continued)

  19. Circuit Switching can be summarized as under: • Hunt for outgoing line • Request for Connection • Connection Acceptance • Message Transmission • Disconnection

  20. MESSAGE SWITCHING • When this form of switching is used, no physical path is established in advance between the sender and receiver. • The central switching station receives all the communication sent to it by all computer sent to it by all computer stations. • Message Switching refers to a process in which intermediate node stores the complete message temporarily and inspects it for errors and transmits the message to the next node based on the available free channel. (To be continued)

  21. Message Switching reduces the traffic congestion on the network because of Store and Forward facility. • Channels are used only when messages are transmitted, so this method uses the channels very effectively. • This method is only used when message delays are not critical. • Systems using message switching require large amount of buffer memory to hold the received message.

  22. PACKET SWITCHING • Packet Switching is a technique in which a long message is divided into many packets and then routing them individually by the network depending on the availability of channel for each packet. • Sequencing is done on the packets to ensure that at a destination packets are combined in order to convert it back to the message. • Packet Switching requires no dedicated circuit i.e it doesn't require any end to end path for data transmission from source to destination. (To be continued)

  23. Intermediate node doesn’t have to wait for the entire message as routing is done on the packet basis. • The first packet can be send as soon as it is available. • Each packet has a header which contains control information i.e source and destination address, message number, packet number and number of bits. • Packet Switching is of 2 types: - Virtual Circuit Packet Switching - Datagram Packet Switching

  24. ISDN • ISDN originally “INTEGRIERTES SPRACHUND DATENNETZ”. • Introduced in late 1980’s • It is a new communication standard for providing an end to end connectivity for digital transmission over an ordinary copper wire. • It is designed to replace the existing local analog Public switched telephone network (PSTN) • Due to introduction of internet old telephone systems are not able to meet all the requirements. so ISDN is introduced • ISDN technology supports audio, video, internet applications • ISDN Technology provides very fast speed of communication.

  25. FEATURES OF ISDN • Offers point to point delivery of data. • Provides for network access and network interconnection for multimedia. • Call setup times with in one second. • Connecting remote users to LAN • Provides a data rate of 2mbps on a local link and 64 kbps/128 kbps over wide area link. • High speed internet access • Allows multiple devices to share a single line • Digital n/w services can be implemented in the existing telephone network.

  26. ISDN SERVICES There are three types of services that are supported by ISDN: • Bearer Services • Tele Services • Supplementary Services

  27. ISDN PRINCIPLES a) Support of voice and non voice applications using a limited set of standardized facilities.This principle defines the purpose of ISDN and the means of achieving it. ISDN support voice communication (telephone calls) and non voice communication (digital data exchange). b) Support for switched and non switched applications:ISDN will support for circuit switching and packet switching. ISDN will support for non switched services in the form of dedicated lines. c) Reliance on 64 kbps connection:ISDN provides circuit switched and packet switched connection at 64 kbps. d)Intelligence in the network:ISDN provides network management and maintenance capabilities. e)Layered protocol architecture:ISDN protocols exhibit a layered architecture and can be mapped to OSI model(open system interconnections). This allows gradual implementation of ISDN services to a given customer base. f)Variety of configurations:More than one physical configuration is possible for implementing ISDN and provides the usage of existing equipment of the customer base.

  28. MULTIPLEXING • In telecommunications and computer networks, multiplexing (also known as muxing) is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. • The aim is to share an expensive resource • A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

  29. FDM (Frequency Division Multiplexing) • The available bandwidth of a physical medium is divided into several smaller logical bandwidths. • In FDM, multiple channels are combined onto a single aggregate signal for transmission. The channels are separated in the aggregate by their frequency. • When FDM is used in a communication network, each input signal is sent and received at maximum speed at all times. • The best example of FDM is the way we receive various stations in a radio.

  30. WDM (Wavelength Division Multiplexing) • WDM is a technique in which various light waves from different sources are combined to form a composite light signal that is transmitted across a channel to the receiver. • WDM systems are popular with telecommunications companies because they allow them to expand the capacity of the network without laying more fiber. • The main components of WDM are: - Combiner - Long Routed Fiber - Splitter - Filter

  31. TDM (Time Division Multiplexing) • TDM can be handled entirely by digital electronics. • TDM is a technology that transmits signals simultaneously over a single transmission path on the basis of time. • Total time available in the channel is divided between several users. Each user is allotted a particular time interval called time slot during which data is transmitted by that user. • The best example of TDM is television broadcast. • In Time Division Multiplexing, channels "share" the common aggregate based upon time.

  32. MODEMS • Modem stands for Modulator/Demodulator. • Internet access requires a device known as Modem which has 2 interfaces on it, one on the computer and one to the network. • The process of Modulation and Demodulation i.e the conversion of digital data in analog form and conversion of analog form to digital form is carried out by a special device called a Modem. • Modem is of two types: - Internal Modem - External Modem

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