Isolation of Wireless Ad hoc Medium Access Mechanisms under TCP Ken Tang,Mario Correa,Mario Gerla Computer Science Department,UCLA
Introduction For mobile computing to be successful, an obvious layer, the MAC layer, must be efficient in channel access and reservation Provide the insights into the design of contemporary wireless, ad hoc random access MAC layer protocols
Wireless MAC Protocols CSMA — Carrier Sense Multiple Access MACA — Multiple Access with Collision Avoidance MACAW FAMA — Floor Acquisition Multiple Access IEEE
CSMA,FAMA,and MACA CSMA: solely uses carrier sense FAMA: utilizes carrier sense with RTS/CTS control frames MACA: digresses from the carrier sensing of FAMA and instead ops for packet sensing
MACAW and IEEE MACAW: adds on top of MACA link- level ACKs, among other features IEEE : coalesces FAMA, link- level ACKs and collision avoidance
Experimental configuration Consider several topologies(Fig1~Fig4) Channel bandwidth are 2Mbps Transmission and propagation delays are modeled Processing delay is negligible
Experimental Topologies
Experimental configuration Each node has a 25-packet MAC layer buffer pool Scheduling of packet transmission is FIFO
Hidden Terminal Topology is as figure 2 node_1 is in radio range of node_0 and node_2 node_0 and node_2 are not within reception range of each other Connections are set up from node 0 to node 1 and node 2 to node 1
Exposed Terminal Topology is as figure 3 node_0 is in range of node_1 node_3 is in range of node_2 node_1 is in range of both node_0 and node_2 node_2 is in range of both node_1 and node_3 Connection are 1 to 0 and 2 to 3
Simulation platform OS : FreeBSD Simulation code : GloMoSim Traffic type : FTP with infinite backlog at each source node TCP packet : fix at 1460B TCP connection : starts uniformly, distributed between 0 to 10 sec
Results PSMA and CSMA works best overall compared to CSMA/CA RTS/CTS control frames assist to provide fairness to the network ACKs in general improve the cumulative throughput of the network environment The combination that works best is CSMA/CA/RTS/CTS/ACK
Conclusion CSMA/CA/RTS/CTS/ACK provide the best overall network service under general terms CSMA/CA/RTS/CTS/ACK is exactly the IEEE standard with virtual carrier sense enabled