MACA-BI(MACA By Invitation)
A Wireless MAC Protocol for High
Speed ad hoc Networking
컴퓨터 및 정보통신공학과
200730038
김 연주
목차
■ 논문 소개
■ Introduction
■ MACA-BI Illustrated
■ Collisions in MACA-BI
■ Predicting Traffic
■ MACA-BI Performance
■ Conclusion
논문 소개
논문 소개
■ Introduction to MACA-BI
■ Show that MACA-BI outperforms other multiple access
protocol in high speed
Introduction
Introduction (1/3)
■ MACA
 Solves the hidden terminal problem
 Outperforms CSMA in a Wireless multi-hop network
■ MACA with Carrier Sensing (FAMA-NTR)
 Can perform almost as well as CSMA in a single-hop wireless
network
■ FAMA-PJ, CARMA
 Achieve better performance at high load
■ MACAW
 Five-way handshake
 Overhead cause low channel utilization!
• TX-RX turn-around time, preamble bits, control bits, checksum
bits
Introduction (2/3)
■ In order to better appraise the turn-around overhead,
every transmission should be delayed by TX to RX turnaround time to give a chance to the previous
transmitter to switch to receive mode.
■ The relative impact of turn-around time becomes more
critical at high channel speed and low propagation
delays.
 So turn-around time is important role in future high
speed, indoor wireless LANs and, more generally,
multihop ad hoc networks!!
Introduction (3/3)
■ MACA-BI (MACA By Invitation)
 Reduces the turn-around time
 Two handshake
 Waits for an “Invitation” by the intended receiver in the
form of an RTR (Ready to Receive) control packet
MACA-BI Illustrated
MACA-BI Illustrated (1/2)
■Three basic cycles of the MACA protocol
“driven by the transmitter”
The three-way handshake
A
RTS
C
B
A
CTS
C
B
A
DATA
B
C
Blocked
MACA-BI Illustrated (2/2)
■Two basic cycles of the MACA-BI protocol
The two-way handshake
■Node B does not have exact knowledge of packet arrival times at Node A
■The each data packet carries the information
Backlog in transmitter: # of packet and their lengths, the average rate
and future backlog
■Node A replies with the transmission of the requested number of packet
and with new backlog information
A
RTR
C
B
A
DATA
B
C
Blocked
Collisions in MACA-BI
Analysis of collision states (1/3)
■ Examination
 6 node hidden terminal configuration
 Identify possible collisions
 Node A and B issue RTRs at about the same time to
different neighbors
 Only three possible combinations
■ Two type of RTR collision
 Direct collision
• Between nodes within hearing distance (due to carrier
sense failure)
 Indirect collision
• Between nodes hidden from each other and transmitting to
a common neighbor
Analysis of collision states (2/3)
Analysis of collision states (3/3)
■ If node receives the RTR packet,
 Knows the duration of the impending data packet data
packet transmissions by its two-hop neighbors
 Is able to decide if its transmission can disturb its
neighbors reception
Data collision free property (1/2)
■ No collision among data packet in MACA-BI
■ Direct collision among data packet
 A transmits data packet to B, then C cannot transmits
data packet to B
 Only if C did not hear the RTR from B to A, C can
transmit a data packet to D
• B transmitted RTR to A while C was transmitting->
impossible!
• B transmitted RTR to A while C was receiving a RTR from
D -> impossible!
Data collision free property (2/2)
■ Hidden terminal problem은 여전히 control packet을 방해
■ RTR과 Data packet간에 충돌 가능
■ Carrier Sensing 실패로 Control Packet간에 충돌 가능
■ MACA-BI는 이러한 충돌 가능성이 존재하지만, MACA는
이러한 충돌을 줄이려고 하지 않는다.
Comparing MACA & MACA-BI protocol
states (1/4)
■ Assume
 The channel is symmetric as in all other MACA
protocols
 Control packet can be corrupted by noise
 Direction collision
 Indirection collision
Comparing MACA & MACA-BI protocol
states (2/4)
■ Direction Collision
Comparing MACA & MACA-BI protocol
states (3/4)
■ Indirection Collision
Comparing MACA & MACA-BI protocol
states (4/4)
■ If the protocols work properly, they are data collision
free
■ Cannot speculate a priori on the probability of each
configuration, but can qualitatively say that introducing
the third pass in the handshake (as MACA dose) does
not reduce the dangerous situations
■ 프로토콜은 channel noise나 fading등으로 control packet
방해를 받아 실패 할 수 있는데 MACA가 MACA-BI보다 훨
씬 취약!
Predicting Traffic
MACA-BI performance
MACA-BI performance (1/8)
■ MACA-BI multi-hop network는 시뮬레이션을 통해 조사
■ 시뮬레이션
 Four nodes
 네트워크의 기본적인 기능, data link, MAC layer는 구현
 Routing은 Bellman-Ford scheme
 모든 node는 size 50의 buffer를 공유
 Data link layer는 선택적인 반복을 가진 size 8의 sliding
window
• separate window는 각 pair node가 사용
 Flow control은 sliding window mechanism을 통해 공급
 Separate MAC protocol 시뮬레이션 모듈은 개발
MACA-BI performance (2/8)
■ 시뮬레이션 (계속)
 Neighbor with highest buffer occupancy is invited to transmit
 Channels are error free
 Packet transmission can collide due to the hidden terminal
problem and the non negligible propagation delay
 방해받은 packet들은 sliding window mechanism에 의해 재 전송
-> packet loss는 오직 네트워크 레벨에서만 발생
 FAMA-NTR은 매 handshake마다 하나의 data packet을 전송
 Floor 충돌이 반복되는 것을 막기 위해 Poisson process를 가진
floor로 node들은 reschedule
 Datagram traffic을 시뮬레이션하기 위해 Poisson process를 가진
모든 노드들에서 External packet들 발생
MACA-BI performance (3/8)
■ 첫 번째 시뮬레이션
 Null propagation time의 1Mbps의 링크
 Control packet 4 bytes
 Data packet 1000bits
 Floor generation interval 2.5ms
MACA-BI performance (4/8)
MACA-BI performance (5/8)
■ 두 번째 시뮬레이션
 유한한 propagation time
 전송 범위 3미터의 near-filed signal strength
 Four node
 10Mbps channel speed
 Average floor generation interval 0.3ms
 Data packet size 53 bites
 Control packet size 4 bytes
MACA-BI performance (6/8)
MACA-BI performance (7/8)
MACA-BI performance (8/8)
Conclusion
Conclusion
■ Eliminate RTS packet
 Reducing the overhead for each packet transmission
 Simplifying the implementation
■ More robust to hidden terminal collision, direct collision
and noise corruption
■ Not very sensitive to the TX-RX turn-around time
■ In simulation, shows its superiority
Q&A