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Introduction To Computer Networking

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Published in: Networking
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A computer network is a set of computers connected together for the purpose of sharing resources. The most common resource shared today is connection to the Internet. Other shared resources can include a printer or a file server.

Prantik S / Kolkata

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Qualification: MCA (Jaipur National University - [JNU], Jaipur - 2017)

Teaches: Basic Computer, Computer for official job, MS Office, School Level Computer, ICT Training, Computer Science, Information Practice, IT & Computer Subjects, BCA Tuition, IT, Computer, C / C++, C# (C Sharp), Java And J2EE, Python Programming, Visual Basic, BCA Subjects, Hardware Training, Networking, Java Script

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  1. Peer-to-peer Server-based Introduction to Networking
  2. What is a Network? A network consists of 2 or more computers connected together, and they can communicate and share resources (e.g. information) D
  3. Why Networking? Sharing information — i.e. data communication Do you prefer these? , Or this?
  4. Sharing hardware or software E.g. print document Centralize administration and support E.g. Internet-based, so everyone can access the same administrative or support application from their PCs Modem Modem Modem Modem
  5. How many kinds of Networks? ' Depending on one's perspective, we can classify networks in different ways Based on transmission media: Wired (UTP, coaxial cables, fiber-optic cables) and Wireless Based on network size, LAN and WAN (and MAN) Based on management method: Peer-to-peer and Client/Server Based on topology (connectivity): Bus, Star, Ring ,
  6. Transmission Media Two main categories: Guided — wires, cables Unguided — wireless transmission, e.g. radio, microwave, infrared, sound, sonar t We will concentrate on guided media here: Twisted-Pair cables: Unshielded Twisted-Pair (UTP) cables Shielded Twisted-Pair (STP) cables Coaxial cables Fiber-optic cables
  7. Twisted-Pair Cables If the pair of wires are not twisted, electromagnetic noises from, e.g., motors, will affect the closer wire more than the further one, thereby causing errors 4 3 4 3 Noise source O 4 3 he total effect i 4 3 7
  8. Unshielded Twisted-Pair (UTP) Typically wrapped inside a plastic cover (for mechanical protection) A sample UTP cable with 5 unshielded twisted pairs of wires Plastic cover Twisted pairs (5 pairs) Insulator Metal 8
  9. Shielded Twisted-Pair (STP) STP cables are similar to UTP cables, except there is a metal foil or braided-metal-mesh cover that encases each pair of insulated wires Plastic cover Metal shield Insulation Copper
  10. Categories of UTP Cables EIA classifies UTP cables according to the quality: Category 1 — the lowest quality, only good for voice, mainly found in very old buildings, not recommended now Category 2 — good for voice and low data rates (up to 4Mbps for low-speed token ring networks) Category 3 — at least 3 twists per foot, for up to 10 Mbps (common in phone networks in residential buildings) Category 4 — up to 16 Mbps (mainly for token rings) Category 5 (or 5e) — up to 100 Mbps (common for networks targeted for high-speed data communications) Category 6 — more twists than Cat 5, up to 1 Gbps
  11. Coaxial Cables In general, coaxial cables, or coax, carry signals of higher freq (IOOKHz-500MHz) than IJTP cables Outer metallic wrapping serves both as a shield against noise and as the second conductor that completes the circuit Plastic cover Insulator Outer conductor Inner conductor (shield) 11
  12. Advantages and Disadvantages o Noise resistance — external light is blocked by outer jacket o Less signal attenuation —a signal can run for miles without regeneration (currently, the lowest measured loss is about or 0.16dB per km) o Higher bandwidth — currently, limits on data rates come from the signal generation/ reception technology, not the fiber itself Cost — Optical fibers are expensive Installation/maintenance — any crack in the core will degrade the signal, and all connections must be perfectly aligned
  13. Fiber-Optic Cables Light travels at 3x108 ms-I in free space and is the fastest possible speed in the Universe Light slows down in denser media, e.g. glass Refraction occurs at interface, with light bending away from the normal when it enters a less dense medium Beyond the critical angle total internal reflection
  14. An optical fiber consists of a core (denser material) and a cladding (less dense material) Simplest one is a multimode step-index optical fiber Multimode = multiple paths, whereas step-index = refractive index follows a step-function profile (i.e. an abrupt change of refractive index between the core and the cladding) Light bounces back and forth along the core Common light sources: LEDs and lasers Core Cladding
  15. LAN and WAN Local Area Network (LAN) Small network, short distance A room, a floor, a building Limited by no. of computers and distance covered ' Usually one kind of technology throughout the LAN Serve a department within an organization Examples: Network inside the Student Computer Room Network inside CF502 Network inside your home
  16. Wide Area Network (WAN) A network that uses long-range telecommunication links to connect 2 or more LANs/computers housed in different places far apart. Towns, states, countries Examples: Network of our Campus Internet WAN Student Computer Centre Your home USA 16
  17. , Example WAN technologies: , ISDN — Integrated Service Digital Network Basic rate: 192 Kbps Primary rate: 1.544Mbps T-Carriers — basically digital phone lines , Tl: 1.544Mbps T3: Frame relay Each link offers 1.544Mbps or even higher ATM — Asynchronous Transfer Mode , Support B-ISDN: 155Mbps or 622Mbps or higher , SONET — Synchronous Optical Network , Basic rate OCI: 51.84Mbps ' Support OC12 and up to OC192 (9953.28Mbps) or even higher in the future
  18. , Example of WAN: Broadband Cable Network , Cable TV services have been extensively developed in most modern cities Cable TV companies try to make use of their coaxial cable installed (that are supposed to carry TV signals) to deliver broadband data services Many cable network wiring has been replaced with hybrid fiber-coax (HFC) — i.e. use of fiber-optic cable to connect to the subscribers' buildings, and then the original coaxial cable to connect to each household 18
  19. PC TV oaxla Cable glÉÅ The connection is shared by a number of subscribers, hence may raise performance and security problems able Drop Cable company 19
  20. ' Cable is an asymmetrical technology Downstream: max 36 Mbps ' Upstream: max 10 Mbps May be reduced to 3 — 10 Mbps downstream and 2 Mbps upstream, depending on no. of subscribers Need a special cable modem Teryon Cable Modem Coaxial link from cable TV socket Ethernet link to PC 20
  21. Peer-to-peer Networks Peer-to-peer network is also called workgroup No hierarchy among computers all are equal No administrator responsible for the network Peer-to-peer
  22. Advantages of peer-to-peer networks: Low cost ' Simple to configure ' User has full accessibility of the computer Disadvantages of peer-to-peer networks: May have duplication in resources Difficult to uphold security policy Difficult to handle uneven loading Where peer-to-peer network is appropriate: 10 or less users No specialized services required ' Security is not an issue Only limited growth in the foreseeable future
  23. Clients and Servers Network Clients (Workstation Computers that request network resources or services Network Servers Computers that manage and provide network resources and services to clients ' Usually have more processing power, memory and hard disk space than clients , Run Network Operating System that can manage not only data, but also users, groups, security, and applications on the network Servers often have a more stringent requirement on its performance and reliability 23
  24. Advantages of client/server networks Facilitate resource sharing — centrally administrate and control Facilitate system backup and improve fault tolerance Enhance security — only administrator can have access to Server ' Support more users — difficult to achieve with peer-to- peer networks Disadvantages of client/server networks High cost for Servers Need expert to configure the network Introduce a single point of failure to the system 24
  25. Topology — 3 basic types How so many computers are connected together? Bus Topology Star Topology Hub Ring Topology
  26. , Bus Topology ' Simple and low-cost A single cable called a trunk (backbone, segment Only one computer can send messages at a time Passive topology - computer only listen for, not regenerate data Star Topology Each computer has a cable connected to a single point More cabling, hence higher cost All signals transmission through the hub; if down, entire network down Depending on the intelligence of hub, two or more computers may send message at the same time 26
  27. How to construct a network with Bus / Star Topology? Bus Topology Coaxial cable Network Card Distribution rack and shelves Expandable patch panels Star Topology BNC T-Connector
  28. Ring Topology Every computer serves as a repeater to boost signals Typical way to send data: Token passing only the computer who gets the token can send data Disadvantages Difficult to add computers More expensive Ack data Ack Ack If one computer fails, whole network fails data Ack 28

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