Using Collisions to improve Network protocols By Gregg Bachmeyer for CMPE 257 Overview How to use collisions as beneficial part of a network protocol Ask the right questions at the base station Break the system into parts Contention Wireles s client 2 Wireles s client 3 Wireles s client 1 Base join May get congested Preventing anyone from Joining Sending Wireles s client 5 Base statio n Wireles s client 4 Why It Might Be Important Growing number of wireless devices may compete for network usage Helps support power savings at client nodes base station assume to be grid powered Most used networks appear to have access points Randomness can give random performance Scheduling Phases Join Notify Schedule Query Schedule Execution Nodes Send and Receive Dead Time Join Notification Phase Schedule Query Schedule Execution Dead Time Join Notification Phase Join Notification Phase Base station send join notification MAC of base station begin MAC address question number of supported frequencies number of members number of collisions List Items continued Size of Packet end mac address question list of frequencies list members of network list collisions of network with frequencies MAC address of node Size of Packet Nodes join Size of Frequency List List of Capable Frequencies Size of Collision List List of Collisions Nodes report on conflicts Number of Packets Max Size Of Packets Checksum Nodes report that they want to send if joining If there is a collision the base station breaks MAC address in 2 based on last digit and resends Schedule Query 32 3D 5628 BA A5 82 3A 4628 5A A3 32 3D 5628 B5 A1 32 65 5623 BA B5 32 3D 5528 55 A2 56 3D 5628 BA FF Base Station Has Nodes added into a tree Base Station Sends Schedule Query MAC of base station begin MAC address question number of hosts that still want to broadcast continued Nodes send If size of packet end mac address question hosts that want to broadcast respond with packets they want to MAC address of node number of packets to send Checksum Max Size of Packets here is a collision the base station divides tree in half and resends Schedule Query Schedule Execution Dead Time Base station sends out schedule MAC of base station Number Of Schedules MAC address From continued Nodes Size Of Packet MAC Address To Frequency Time Begin Time End wait for there time and send or receive The schedule can include areas of Dead Time so that frequencies can be shared Start from the beginning Join Notify Phase Expectations better than 802 11 Large number of nodes with intermittent amount of data to send Or nodes that have large number of packets to send at one time worse than 802 11 Small number of nodes worse than 802 11 Nodes that only have one packet to send at a time worse than 802 11 MAC addresses that are inversely sequential but MAC addresses are changeable Simulation Setup NS 2 802 11 Collision protocol Increasing number of non mobile wireless nodes jump 30 nodes at a time Packet arrival at 0003 TCP AODV layers stacked above Current Output packet throughput in 10 sec period 5000 4500 4000 3500 3000 802 11 coll net 2500 2000 1500 1000 500 0 2 32 Note 62 92 122 152 182 212 242 272 302 332 362 392 this is current output at time of presentation I think that there are errors that are causing only one packet to arrive at a time that I am working on correcting Expected Issues on Real Implemention Possible large amount of overhead Fast processing on base station Current physical handling of collisions may prevent the possibility of the protocol working Conclusion The overhead of the protocol may be high for use today but its necessity for the future is possible There are many possible heuristics that should be considered or future research that may improve performance to help it compete with protocols used today Questions References Venkatesh Rajendran Katia Obraczka J J Garcia Luna Aceves DYNAMMA A DYNAmic Multi channel Medium Access Framework for Wireless Ad Hoc Networks Proceedings of the 4th IEEE International Conference on Mobile Ad hoc and Sensor Systems MASS Oct 2007 John R Vacca Wireless Data Demystified McGraw Hill Networking 2002 SourceForge Ns 2
View Full Document
Unlocking...