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FAMA for Packet-Radio Networks

Explore the FAMA protocols for improving MAC performance in single-hop networks. Learn about Floor Acquisition Multiple Access, collision avoidance methods, theorems, slotted versions, performance evaluation, and comparison with existing protocols.

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FAMA for Packet-Radio Networks

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  1. FAMA for Packet-Radio Networks Reddy Mainampati Udit Parikh Alex Kardomateas

  2. Background and Motivation • CSMA protocols are used in packet radio networks • CSMA/CD cannot be used • Motivation: to increase throughput on single hop networks with no hidden terminal problem

  3. The Problem Statement • The present MAC protocols do not prevent data packets from colliding with RTS/CTS • What can ensure that data packets do not collide?

  4. Introduction • FAMA – Floor Acquisition Multiple Access for Packet Radio Networks • Objectives: floor acquisition and collision avoidance • Solutions: RTS/CTS dialogue and carrier sensing • Results: Improvement in performance of MAC protocols

  5. FAMA Protocols • MACA (Multiple Access Collision Avoidance) • RTS/CTS exchange with no carrier sensing • FAMA-NTR (Non-persistant Transmit Request) • RTS/CTS exchange with non-persistant carrier sensing

  6. Theorem 1 • Theorem 1: FAMA-NTR ensures that each new data packet, or any of its retransmissions, is sent to the channel within a finite time after it becomes ready for transmission and that a data packet does not collide with any other transmission provided that τ < γ < ∞ • Τ(tau) – maximum propagation delay • γ – transmission time of RTS/CTS

  7. Theorem 2 • Theorem 2: MACA ensures that data packets do not collide with any other transmissions provided that 2τ < γ < ∞

  8. Slotted FAMA • Global clocks can be used for stations to transmit synchronously. • Slotted MACA • Slotted FAMA-NTR • Slotting helps in performance improvement over the basic protocols.

  9. Performance Evaluation Model • Approximate Throughput Analysis • Non-persistent CSMA,MACA,FAMA-NTR and the slotted versions • Assume that stations can listen to transmissions of all other stations.

  10. Channel Utilization • Average Channel Utilization (S) • S=U/(B+I) • U= Time taken by the station to transmit data successfully. • Use factors such as δ(data transmission time), τ and γ.

  11. Performance Comparison • a = τ/δ (normalized propagation delay) • b = γ/δ (normalized control packets) • G = λ x δ (Offered Load, normalized to data packets) • Use of graphs to show throughput comparison between different FAMA protocols

  12. Non persistant CSMA vs FAMA

  13. Related Work • FAMA variants • Apple’s Local Talk link access protocol • IEEE 802.11 • MACAW protocol • MACA with no carrier sensing

  14. Critique • Use of only single-hop networks • FAMA only work without hidden terminal problems • Paper does not address channel stability and optimization. • Model for analysis is a rough approximation of the real world scenario.

  15. Summary and Conclusions • FAMA permits total control of the channel for one station at a time • RTS/CTS control dialogue and carrier sensing eliminate collisions for data packets and substantially increases channel throughput

  16. QUESTIONS?

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