1. Isolation of Wireless Ad hoc Medium Access Mechanisms under TCP Ken Tang,Mario Correa,Mario Gerla Computer Science Department,UCLA

2. 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

3. Wireless MAC Protocols CSMA — Carrier Sense Multiple Access MACA — Multiple Access with Collision Avoidance MACAW FAMA — Floor Acquisition Multiple Access IEEE 802.11

4. 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

5. MACAW and IEEE 802.11 MACAW: adds on top of MACA link- level ACKs, among other features IEEE 802.11: coalesces FAMA, link- level ACKs and collision avoidance

6. Experimental configuration Consider several topologies(Fig1~Fig4) Channel bandwidth are 2Mbps Transmission and propagation delays are modeled Processing delay is negligible

7. Experimental Topologies

9. Experimental configuration Each node has a 25-packet MAC layer buffer pool Scheduling of packet transmission is FIFO

10. 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

11. 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

12. Simulation platform OS : FreeBSD 2.2.4 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

13. 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

14. Conclusion CSMA/CA/RTS/CTS/ACK provide the best overall network service under general terms CSMA/CA/RTS/CTS/ACK is exactly the IEEE 802.11 standard with virtual carrier sense enabled