Announcements CMPE 257 Wireless and Mobile Networking n First reading report assigned n n n Spring 2003 Lecture 5 CMPE 257 Spring 2003 Due date 04 24 2003 Reminders n Project 2 proposal due 04 17 2003 Project 1 due 04 22 2003 1 CMPE 257 Spring 2003 Today MACAW Finish MACs n MACAW cont d DVCS PAMAS n 2 Inspired 802 11 2 basic changes to MACA n n Message exchange Backoff algorithm Mobile IP CMPE 257 Spring 2003 3 CMPE 257 Spring 2003 4 Message Exchange n Backoff Mechanism RTS CTS DATA ACK n n ACK added for reliability n n Tries to avoid the unfairness problem of exponential backoff Proposed fix sharing of congestion information among nodes Backoff counter information in the packet header n n CMPE 257 Spring 2003 5 Message Exchange n RTS CTS DS DATA ACK n A B Addresses exposed terminal problem n n n n n n CMPE 257 Spring 2003 6 More on Message Exchange C Exposed terminal may not get CTS from receiver If B is transmitting to A C cannot hear CTS from A It doesn t know whether RTS CTS succeeded And if it tries to xmit and doesn t get response it backsoff Data Sending DS packet indicates RTS CTS exchange was successful Overhearing stations defer transmission until after ACK slot CMPE 257 Spring 2003 Stations hearing packet copy value as their own backoff counter After successful transmission all stations have same backoff counter 7 n n n RRTS Tries to solve unfairness Use receiver to contend on behalf of sender n If receiver receives RTS and cannot respond with CTS e g it s deferring due to a CTS at next contending period sends RRTS to RTS sender CMPE 257 Spring 2003 8 Directional Antennas and Directional CS n n n CS and Virtual CS Spatial division MA In use in cellular networks Issues in MANETs n n n CS performed at physical layer n Nodes don t know their neighbors a priori Directional antennas may restrict number of neighbors n Virtual CS performed at the MAC layer n Contention based MACs n n n CMPE 257 Spring 2003 9 Directional Antennas and CS n n n RTS CTS Either CS or virtual CS or both IEEE 802 11 DCF CSMA CA with option for Virtual CS CMPE 257 Spring 2003 10 DVCS Goals CS and VCS assume omni directional transmission Physical CS may be impacted by directional xmission n Senses channel and determines level of interference and noise n n n Carrier is no longer good contention indicator Exploit directional antennas But work with omnidirectional ones Supports both directional transmission and reception Virtual CS n Directional RTS and CTS cannot be heard by all neighbors CMPE 257 Spring 2003 11 CMPE 257 Spring 2003 12 IEEE 802 11 with DVCS n n AOA Caching Assume CA i e RTS CTS Changes to 802 11 n n n Nodes cache AOA info from received overheard signals When node wants to Xmit looks up AOA cached info If so beamforms in that direction for RTS Xmission Otherwise RTS Xmitted omnidirectionally Cached info is updated invalidated n n Angle of arrival caching Beam locking unlocking Directional Network Allocation Vector DNAV n n CMPE 257 Spring 2003 13 CMPE 257 Spring 2003 Beam locking unlocking DNAV n n n Maximize Xmission reception in given direction Locking n n Regular 802 11 uses NAV network allocation vector n n After receiving RTS for CTS Xmission After receiving CTS after RTS Xmission n n Unlocking after ACK Xmission n n CMPE 257 Spring 2003 15 NAV virtual CS indicator Time access to medium deferred based on receiving RTS CTS DNAV directional NAV n n 14 Direction and width specific Updated based on physical layer info Directional Xmission channel available when no DNAV covers that direction Omni direction Xmission channel available when no DNAVs CMPE 257 Spring 2003 16 DVCS Example DVCS Example CTS A A RTS B CMPE 257 Spring 2003 RTS 17 DVCS Example A B CMPE 257 Spring 2003 18 DVCS Example CTS DATA B CTS DATA B A B ACK RTS CMPE 257 Spring 2003 B RTS 19 CMPE 257 Spring 2003 B 20 DNAV Direction and Width n Direction set based on AOA n n n Antenna Model n AOA better than direction based on physical location Path losses scattering reflection etc n n n Width n n Narrower beams improve channel utilization Why Omni directional antennas width is 360o DVAV NAV CMPE 257 Spring 2003 n n n 21 n n Simulations using QualNet MAC and physical layer parameters Others number of nodes field size traffic model mobility pattern etc CMPE 257 Spring 2003 n n n n n CMPE 257 Spring 2003 Simulated 10 patterns 0 54o 6o Beamwidth 45o between 0 3dB of max gain DNAV 74o between 0 9dB of max gain 22 Performance Metrics and Scenarios Experimental Setup n Electrically steerable antenna Omni directional operation possible Antenna reports AOA and gain to MAC Antenna patterns change side and back lobes as it changes direction 23 Packet delivery ratio reliability Throughput peak performance Mobility versus no mobility Physical CS versus no physical CS Interoperability with omni antennas CMPE 257 Spring 2003 24 Summary of Results n n Increased network capacity especially with mobility Physical CS helps especially with mobility n n n PAMAS Reduces interference effect caused by concurrent Xmissions No mobility AODV modified not to start route discovery on link breakage when a route exists n Goal energy efficiency Approach n n n Contention based based on MACA Low power radio mode when node is idle Separate signaling channel for RTS CTS DVCS interoperates with 802 11 Performance improvement in mixed settings CMPE 257 Spring 2003 25 Energy model n n Interoperability n n n CMPE 257 Spring 2003 26 PAMAS Protocol Idle mode consumes orders of magnitude less power than transmission or receiver modes Overhearing CMPE 257 Spring 2003 27 CMPE 257 Spring 2003 28 Observations n RTS CTS exchange on separate signaling channel n n Overhearing n n Does not affect data exchange n Busy tone also on signaling channel n n Sent by data receiver Protects receiver from transmissions by neighbors n n 29 Powering off n No packets to transmit and neighbor begins transmitting Packet to send but at last one neighbor is receiving neighbor sends busy tone Collides with RTS CTS exchange from interfering nodes CMPE 257 Spring 2003 n Power off radio to avoid overhearing Nodes power off if CMPE 257 Spring 2003 Duration of Idle Period For how long Use probes to determine duration of idle mode n If node has empty queue powers off for duration of transmission n n n 31 When node comes up if its queue still empty and channel busy uses probes to do binary search to determine time last transmission will end If node has non empty queue transmits RTS when comes up n