FAMA for Packet-Radio
Networks
Reddy Mainampati
Udit Parikh
Alex Kardomateas
1
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
2
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?
3
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
4
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
5
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
6
Theorem 2
Theorem 2: MACA ensures that data
packets do not collide with any other
transmissions provided that 2τ < γ < ∞
7
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.
8
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.
9
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.
10
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
11
Non persistant CSMA vs FAMA
12
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?