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Multiple Access in Computer Network
The document discusses multiple access protocols in the data link layer, specifically detailing random access methods like ALOHA and CSMA variants, along with controlled access methods such as polling and token passing. It also covers channelization techniques including FDMA, TDMA, and CDMA, and provides insights into the evolution of Ethernet standards through various generations and their implementations. The document highlights the importance of bandwidth utilization and the methodology behind different access protocols.
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Multiple Access in Computer Network
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- 2. Data link layerdivided into two functionality-oriented sublayers
- 3. Taxonomy of multiple-accessprotocols discussed in this chapter
- 4. ALOHA Random Access Frames ina pure ALOHA network
- 5. Importance Relevance Significance •To maximize the bandwidth utilization • ALOHA • Carrier Sense Multiple Access • Carrier Sense Multiple Access with Collision Detection • Carrier Sense Multiple Access with Collision Avoidance • In random access or contention methods, no station is superior to another station and none is assigned the control over another. No station permits, or does not permit, another station to send. At each instance, a station that has data to send uses a procedure defined by the protocol to make a decision on whether or not to send.
- 6. • No idlestate How to achieve the maximum utilization? • Multiple send/receive • Avoid Collision • Avoid Trafficking 2 1 3 4
- 7. Procedure for pureALOHA protocol
- 8. Vulnerable time forpure ALOHA protocol
- 9. Frames in aslotted ALOHA network
- 10. Vulnerable time forslotted ALOHA protocol
- 11. Space/time model ofthe collision in CSMA
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- 14. Flow diagram forthree persistence methods
- 15. Collision of thefirst bit in CSMA/CD
- 16. Collision and abortionin CSMA/CD
- 17. Flow diagram forthe CSMA/CD
- 18. Energy level duringtransmission, idleness, or collision
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- 20. Note In CSMA/CA,if the station finds the channel busy, it does not restart the timer of the contention window; it stops the timer and restarts it when the channel becomes idle.In CSMA/CA, the IFS can also be used to define the priority of a station or a frame.
- 21. Flow diagram forCSMA/CA
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- 23. Controlled Access In controlledaccess, the stations consult one another to find which station has the right to send. A station cannot send unless it has been authorized by other stations. We discuss three popular controlled- access methods. 1. Reservation 2. Polling 3. Token Passing
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- 25. Select and pollfunctions in polling access method
- 26. Logical ring andphysical topology in token-passing access method
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- 28. Channelization Channelization is amultiple- access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations. In this section, we discuss three channelization protocols. 1. Frequency-Division Multiple Access (FDMA) 2. Time-Division Multiple Access (TDMA) 3. Code-Division Multiple Access (CDMA)
- 29. FDMA In FDMA, the available bandwidth ofthe common channel is divided into bands that are separated by guard bands.
- 30. TDMA In TDMA, the bandwidthis just one channel that is timeshared between different stations.
- 31. CDMA In CDMA, one channelcarries all transmissions simultaneously. Simple idea of communication with code
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- 35. Digital signal createdby four stations in CDMA
- 36. Decoding of thecomposite signal for one in CDMA
- 37. General rule and examplesof creating Walsh tables The number of sequences in a Walsh table needs to be N = 2m.
- 38. Reference Author: Behrouz A.Forouzan Publication:· Book Data Communications and Networking (McGraw-Hill Forouzan Networking) McGraw-Hill Higher Education ©2007 ISBN:0072967757
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- 40. IEEE STANDARDS In 1985,the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among equipment from a variety of manufacturers. Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols. 1. Data Link Layer 2. Physical Layer
- 41. STANDARD ETHERNET The originalEthernet was created in 1976 at Xerox’s Palo Alto Research Centre (PARC). Since then, it has gone through four generations. We briefly discuss the Standard (or traditional) Ethernet in this section. 1. MAC Sublayer 2. Physical Layer
- 42. Ethernet evolution throughfour generations
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- 44. Minimum and maximumlengths Frame length: Minimum: 64 bytes (512 bits) Maximum: 1518 bytes (12,144 bits)
- 45. Example of anEthernet address in hexadecimal notation
- 46. Unicast and multicastaddresses
- 47. Note The least significantbit of the first byte defines the type of address. If the bit is 0, the address is unicast; otherwise, it is multicast. The broadcast destination address is a special case of the multicast address in which all bits are 1s.
- 48. Categories of StandardEthernet
- 49. Encoding in aStandard Ethernet implementation
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- 54. Summary of StandardEthernet implementations
- 55. CHANGES IN THESTANDARD
- 56. CHANGES IN THESTANDARD The 10-Mbps Standard Ethernet has gone through several changes before moving to the higher data rates. These changes actually opened the road to the evolution of the Ethernet to become compatible with other high-data-rate LANs. 1. Bridged Ethernet 2. Switched Ethernet 3. Full-Duplex Ethernet
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- 58. A network withand without a bridge
- 59. Collision domains inan unbridged network and a bridged network
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