HandoffDelayfor802.11b-ColumbiaUniversity.ppt

Handoff Delay for 802.11b Wireless LANs Masters Project defense Anshul Jain Committee: Dr. Henning Schulzrinne, Columbia University Dr. Zongming Fei, University of Kentucky Dr. Jim Grffioen, University of Kentucky Dr. Ken Calvert, University of Kentucky Overview The IEEE 802.11 Wireless LAN architecture Channel Allocation 802.11 Management Frames Handoff Procedure Experimental Setup Configuration Problems Details of Experiments Summary of Experiments Conclusion The IEEE 802.11 Wireless LAN architecture Wireless LAN Station (STA) Access Points (AP) Basic Service Set (BSS) Distribution System (DS) Extended Service Set (ESS) The IEEE 802.11 Wireless LAN architecture (cont.) Two different ways to configure a network Ad-hoc No structure Every node can talk to each other Infrastructure Fixed APs with which mobile nodes can communicate APs are connected to DS Channel Allocation 83.5 MHz from 2.4000 GHz to 2.4835 GHz 11 channels, each channel being 22 MHz in width, and each channel centered at 5 MHz intervals 802.11 Management Frames Authentication Deauthentication Association request Association response Reassociation request Reassociation response Disassociation Beacon Probe request Probe response Handoff Procedure Mobile node moves from coverage area of one AP to that of another AP Steps During Handoff Discovery Initiation and scanning phase Active and passive scanning mode Reauthentication Authentication and re-association Handoff Procedure (cont.)Active Scanning Mode procedure Transmit a probe request frame which contains the broadcast address as the destination. Start a probe timer. Listen for probe response. If no response received by minChannelTime, scan next channel. If one or more responses are received by minChannelTime, stop accepting probe responses at maxChannelTime and process all received responses. Move to next channel and repeat above steps. Handoff Procedure (cont.) Sequence of messages exchanged between the mobile node and the participating APs. Pr