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Computer network (Lecture 1)
A network connects computers and allows sharing of resources and communication between users. It can be a LAN spanning a single building, a MAN connecting LANs in a city, or a global WAN like the Internet. Networks transmit data over various media like twisted pair cable, fiber, and wireless signals. Proper use of media and protocols allows networks to function according to the OSI model.
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Explanation of networks including LAN, MAN, and WAN definitions, capabilities, and scale.
Reasons for using a layered approach in networking: resource sharing, design specialization, troubleshooting, and standards.
Introduction to the OSI model, detailing its seven layers and their specific functions in data transmission.
Comparison between OSI and TCP/IP models emphasizing protocols, standardization, and structural differences.
Different types of transmission media including guided (twisted pair, coaxial, fiber) and unguided (microwave, wireless) media.
Details on optical fibers, types (multimode, single mode), and their advantages in networking.
Overview of wireless transmission methods, including types of antennas, frequencies, and their applications.
Explanation of challenges in wireless communication such as line of sight issues, free space loss, and atmospheric effects.
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Computer network (Lecture 1)
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- 2. What is anetwork? q A network can be anything from a simple collection of computers (two connected computers qualify as a network) at one location that have been tied together using a particular connectivity medium (such as network cabling or wireless technology) to a giant global network, such as the Internet, that uses a number of different connectivity media, including microwave and satellite technology. The network can then be used to transmit data, voice, and even video between users on the network.
- 3. Defining LANs, MANs,and WANs q Local Area Network (LAN): A LAN supports fast, low−error data transfer on a physical network infrastructure that covers a small, limited geographic area, such as within a single building or on a single floor of a building.
- 4. Metropolitan Area Network (MAN): A MAN is a network that spans an area larger than a LAN but is less dispersed geographically than a WAN. A MAN network may connect several LANs on a single companys campus, or interconnect the LANs of several companies and businesses in one part of town, Wide Area Networks (WAN): A WAN,, is a network that interconnects LANs and MANs across a broad geographic area
- 5. A local AreaNetwork
- 6. A Wide AreaNetwork
- 7. Why Network YourComputers? q Users can share resources and communicate File sharing. Hardware sharing (printers, CD-ROM drives, and hard drives ) Program sharing User communication. Multiplayer gaming
- 8. Reasons why alayered−model is used Change: changes made to one layer, the impact on the other layers is minimized. Design: protocol designers can specialize in one area (layer) without worrying about how any new implementations affect other layers. Learning: The layered approach reduces the complexity and makes learning ,understanding the actions of each layer and the model on the whole much easier.
- 9. Troubleshooting: The protocols,actions, and data contained in each layer of the model relates only to the purpose of that layer. This enables troubleshooting efforts to be pinpointed on that layer. Standards: Probably the most important reason for using a layered model is that it establishes a prescribed guideline for interoperability between the various vendors developing products that perform different data communications tasks.
- 10. OSI Reference model q The Open Systems Interconnection Reference Model, the OSI model was developed by the ISO (International Standards Organization) and released in 1984. q The OSI model, as it is called for short, defines the rules,mechanisms, formats, and protocols used to guide how data flows from one device to another.
- 11. 1.All People SeemTo Need Data Processing 2. Please Do Not Throw Salami (or Sausage if you prefer) Pizza Away
- 13. Physical Layers q The Physical layer of the OSI model defines the electrical and mechanical specifications used in networking,including transmission distances, the various types of media available, and electrical issues.
- 14. The Data LinkLayer q Physical addressing q Network topology q Error notification q Access to the physical medium (a.k.a. arbitration) q Flow control
- 15. The Network Layer •Message addressing • Path determination between source and destination nodes on different networks • Routing messages between networks • Controlling congestion on the subnet • Translating logical addresses into physical addresses
- 16. When the message(which moves down through the seven OSI layers on Johns computer before its sent out on the local network in binary form) arrives at Router 1, it moves up from the Physical layer to the Data Link layer to the Network layer. At Layer 3, its determined that the message is not on a network attached to Router 1 and the message is sent down through the Data Link layer to the Physical layer and on to Router 3.
- 17. The Transport Layer q Segment and assemble upper−layer applications q Transport segments from one host to another host q Establish and manage end−to−end operations q Error recovery
- 18. The Session Layer q A session is a series of related connection−oriented transmissions between network nodes. q Session Layer, establishes, manages, and terminates sessions between applications. q The session layer provides a name space that is used to tie together the potentially different transport streams that are part of a single application. q Session layer is its role in deciding whether a communications session uses a simplex, half−duplex, or full−duplex transmission mode.
- 19. Presentation Layers q Data encryption q Data compression q Data formatting q Data conversion
- 20. The Application Layer q Application layer defines the communication services used by the users applications to transmit data over the network. q FTP (File Transfer Protocol) q E−mail clients q Web browsers q Telnet q SNMP (Simple Network Management Protocol) q BBS (bulletin board system) servers q EDI (Electronic Data Interchange) and other transaction services
- 21. A Quick Reviewof the OSI Model
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- 23. OSI vs TCPReference Models q OSI introduced concept of services, interface, protocols. These were force-fitted to TCP later ⇒ It is not easy to replace protocols in TCP. q In OSI, reference model was done before protocols. In TCP, protocols were done before the model q OSI: Standardize first, build later TCP: Build first, standardize later q OSI took too long to standardize. TCP/IP was already in wide use by the time. q OSI became too complex. q TCP/IP is not general. Ad hoc.
- 24. TCP/IP Concepts Network AttachmentPoint (NAP)
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- 26. Overview Electromagnetic Spectrum TransmissionMedia: Twisted Pair, Coax, fiber,wireless Unshielded Twisted Pair (UTP) categories Reflection and Refraction Antennas: Isotropic, directional, omni- directional Terrestrial and Satellite Microwave
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- 28. Transmission Media q Guided: Twisted Pair Coaxial cable Optical fiber q Unguided: Microwave Satellite Wireless
- 29. Twisted Pair (TP) q Twists decrease the cross-talk q Neighboring pairs have different twist length q Most of telephone and network wiring in homes and offices is TP.
- 30. Unshielded and ShieldedTP q Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheap, Flexible Easiest to install No shielding Suffers from external EM interference Used in Telephone and Ethernet q Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy) Used in token rings
- 31. UTP Categories q Cat 3 Up to 16MHz Voice grade found in most offices Twist length of 7.5 cm to 10 cm q Cat 4 Up to 20 MHz. Not used much in practice. q Cat 5 Up to 100MHz Used in 10 Mbps and 100 Mbps Ethernet Twist length 0.6 cm to 0.85 cm q Cat 5E (Enhanced), Cat 6, Cat 7
- 32. Coaxial Cable q Higher bandwidth than UTP. Up to 500 MHz. q Used in cable TV
- 33. Reflection and Refraction q Index of Refraction = Speed of light in Vacuum/Speed in glass = 300 m/μs / 200 m/μs =1.5 q Refracted light bends towards the higher index medium
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- 35. Optical Fiber q A cylindrical mirror is formed by the cladding q The light wave propagate by continuous reflection in the fiber q Not affected by external interference =>low bit error rate q Fiber is used in all long-haul or high-speed communication q Infrared light is used in communication
- 36. Types of FibersI q Multimode Fiber: Core Diameter 50 or 62.5 mm q Wide core => Several rays (mode) enter the fiber q Each mode travels a different distance q Single Mode Fiber: 10-μm core. Lower dispersion.
- 37. Types of FibersII q Dispersion-Shifted Fiber: Zero dispersion at 1310nm EDFAs/DWDM systems operate at 1550 nm Special core profile zero dispersion at 1550 nm q Dispersion Flattened Fiber: 3 ps/nm/km 1300-1700nm Use 1300 nm now and 1550 in future Low dispersion causes four-wave mixing DSF/DFF not used in multi-wavelength systems
- 39. Wireless Transmission Frequencies q 2GHz to 60GHz Terrestrial Microwave, Satellite Microwave Highly directional Point to point q 30MHz to 1GHz Omni-directional Broadcast radio q 3 x 1011 to 2 x 1014 Infrared Short distance
- 40. Antenna q Transmitter converts electrical energy to electromagnetic waves q Receiver converts electromagnetic waves to electrical energy q Same antenna is used for transmission and reception q Omni-Directional: Power radiated in all directions q Directional: Most power in the desired direction q Isotropic antenna: Radiates in all directions equally q Antenna Gain = Power at particular point/Power with Isotropic q Expressed in dBi
- 41. Parabolic Antenna Usedin Terrestrial microwaves Line of sight communication 10-60 GHz Higher frequencies for higher data rates
- 42. Terrestrial Microwave q Parabolic dish q Focused beam q Line of sight q Long haul telecommunications q Higher frequencies give higher data rates
- 43. Satellite Microwave Relaystation => Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency Geo-stationary orbit: Height of 35,784km Point to Point or Direct broadcast satellite
- 44. Broadcast Radio q Omni-directional q FM radio, UHF and VHF television q Line of sight q Suffers from multi-path interference (Reflections)
- 45. Infrared q Used in TV remote control q IRD port of computers q Modulate infrared light q Line of sight (or reflection) q Blocked by walls
- 46. Wireless Propagation q Ground wave: Follows contour of earth. Up to 2MHz. AM radio q Sky wave: Signal reflected (Actually refracted) from ionosphere layer of upper atmosphere. Amateur radio, BBC world service, Voice of America q Line of sight: Above 30MHz. Density of atmosphere decreases with height. Results in radio waves bending towards earth
- 48. Line of SightTransmission q Free space loss: Signal disperses with distance Greater for lower frequencies (longer wavelengths) q Atmospheric Absorption: Water vapour and oxygen Water greatest at 22GHz, less below 15GHz Oxygen greater at 60GHz, less below 30GHz Rain and fog scatter radio waves q Multipath: Signal can be reflected causing multiple copies to be received. May be no direct signal at all. May reinforce or cancel direct signal
- 50. Summary q Unshielded twisted-pair (UTP) vs STP q Single mode and multimode optical fiber q Optical communication wavelengths q Isotropic vs omni directional vs directional antennas q Parabolic antenna for microwave q Ground wave, sky wave, line of sight