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 turn-around 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 (1/2) ■Three basic cycles of the MACA protocol “driven by the transmitter” The three-way handshake AB C RTS AB C CTS AB C DATA 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 AB C RTR AB C DATA Blocked
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 (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 problem 은 여전히 control packet 을 방해 ■RTR 과 Data packet 간에 충돌 가능 ■Carrier Sensing 실패로 Control Packet 간에 충돌 가능 ■MACA-BI 는 이러한 충돌 가능성이 존재하지만, MACA 는 이 러한 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 noise 나 fading 등으로 control packet 방 해를 받아 실패 할 수 있는데 MACA 가 MACA-BI 보다 훨씬 취약 !
MACA-BI performance (1/8) ■MACA-BI multi-hop network 는 시뮬레이션을 통해 조사 ■ 시뮬레이션 Four nodes 네트워크의 기본적인 기능, data link, MAC layer 는 구현 Routing 은 Bellman-Ford scheme 모든 node 는 size 50 의 buffer 를 공유 Data link layer 는 선택적인 반복을 가진 size 8 의 sliding window separate window 는 각 pair node 가 사용 Flow control 은 sliding window mechanism 을 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 packet 들은 sliding window mechanism 에 의해 재 전송 -> packet loss 는 오직 네트워크 레벨에서만 발생 FAMA-NTR 은 매 handshake 마다 하나의 data packet 을 전송 Floor 충돌이 반복되는 것을 막기 위해 Poisson process 를 가진 floor 로 node 들은 reschedule Datagram traffic 을 시뮬레이션하기 위해 Poisson process 를 가진 모 든 노드들에서 External packet 들 발생
MACA-BI performance (3/8) ■ 첫 번째 시뮬레이션 Null propagation time 의 1Mbps 의 링크 Control packet 4 bytes Data packet 1000bits Floor generation interval 2.5ms
MACA-BI performance (5/8) ■ 두 번째 시뮬레이션 유한한 propagation time 전송 범위 3 미터의 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
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
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