1. Institut für Betriebssysteme und Rechnerverbund Technische Universität Braunschweig Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman

2. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 2/17 Multi hop Connectivity  Multi hop connectivity is solved for wired networks long ago  Multi hop connectivity for wireless networks is also not new  Many routing protocols like AODV, DSDV, DSR, TBRF etc.  Still no widely accepted solution as we have in wired networks Problem AnalysisAd hoc 802.11 MACFuture Plans

3. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 3/17 Proactive vs. Reactive  Routing in MANETs  Proactive routing protocols –maintain consistent and up-to-date information about the network by constantly exchanging routing information among nodes  Reactive routing protocols –initiate an independent route discovery process whenever a source node requires a route to some destination  Reactive approaches have less overhead but require more time to connect source and destination  Reactive is preferable-more suits to low resource nature  Reactive route discovery requires some attention Problem AnalysisAd hoc 802.11 MACFuture Plans

4. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 4/17 On-demand behavior in AODV  On-demand Features  An approach based only on reaction to the offered traffic  A reactive protocol might have some proactive (not on-demand) features –In AODV, during the route discovery process, if an in-valid route entry is already present in the routing table, the value of TTL field in the RREQ packet’s IP header is initially set to the hop count value in that entry.  In AODV which is a reactive protocol, dependency on proactive features or stale information is not beneficial Problem AnalysisAd hoc 802.11 MACFuture Plans

5. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 5/17 On-demand behavior in AODV  In these simulations  AODV with a reduced proactive feature vs. AODV –Initial value of TTL field will not depend on existing stale entry  AODV with additional proactive feature vs. AODV –Sharing of additional route information Problem AnalysisAd hoc 802.11 MACFuture Plans Learning during Route Discovery

6. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 6/17 On-demand behavior in AODV  Simulation Results  NS2.28 with AODV-UU  100 nodes  40 and 80 source/destination pairs  Node speed 1 m/sec  Pause Time 0 seconds  CBR sources  UDP packets of 1024 Bytes Problem AnalysisAd hoc 802.11 MACFuture Plans

7. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 7/17 Some other Issues  Broadcast transmissions  Used extensively in both Proactive and Reactive protocols for maintaining routing tables  Is just not affordable  No RTS/CTS which means high risk of collision  Scalability is the major problem in ad hoc networks  Number of nodes  Amount of mobility  Offered load Problem AnalysisAd hoc 802.11 MACFuture Plans

8. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 8/17 Ad hoc 802.11 MAC  A multi hop extension for IEEE 802.11 MAC header  It is a reactive or on-demand in nature  Exploit the normal MAC operations –No special route/destination request packet/frame –No special route/destination reply packet/frame  Exploits the use of data frame for destination discovery –reduce the delay for connecting source to destination Problem AnalysisAd hoc 802.11 MACFuture Plans

9. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 9/17 Modifications to 802.11 MAC  Additions to MAC header: Multi hop Data Frame (MDF)  Address1 = Recipient Address (RA)  Address2 = Transmitter Address (TA)  Address3 = Destination Address (DA)  Address4 = Source Address (SA)  An additional 2 Bytes cost field –Hop count Problem AnalysisAd hoc 802.11 MACFuture Plans Octets FCS Frame Body Address 4 SA Sequence Control Address 3 DA Address 2 TA Address 1 RA Duration / ID Frame Control 40-23126266622 Octets Cost 2

10. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 10/17 Modifications to 802.11 MAC  A Forwarding Table is maintained by each node  Destination Address (6 Bytes)  Next Hop (6 Bytes)  Cost (2 Byte)  All 802.11 frames carry unique sequence number and fragment number in sequence control field (SCF)  Nodes maintain a list of MAC address (sender/TA) and SCF value pairs  In Ad hoc 802.11 MAC, original sender is SA and not the TA therefore in SCF list SAs should be stored Problem AnalysisAd hoc 802.11 MACFuture Plans

11. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 11/17 Protocol Components  Three main components  Learning  Forwarding  Repair  Learning: learning about accessible nodes  Whenever a node receives a multi hop data frame –It adds entries in FWT for TA and SA of the frame if there is no entry for either of them –If there is already an entry for either, this entry will be updated  A repair operation will be performed if the cost of previously stored path is less than the new path Problem AnalysisAd hoc 802.11 MACFuture Plans

12. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 12/17 Protocol Components  Forwarding  Originating data frames –If there is an entry for DA in FWT  TA would be the next hop in this entry –Else TA would be broadcast  Relaying frames for other nodes –If DA is broadcast and SCF is new  Broadcast it once again –If DA is uni-cast and SCF is new  Follow same steps as in originating –Frames carrying old SCF will always be dropped Problem AnalysisAd hoc 802.11 MACFuture Plans

13. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 13/17 Protocol Components  Repair  Responsible for identifying anomalies in FWTS  Also share information about these anomalies with other nodes  Path Repair Frame (PRF) –A multi hop data frame with no data in frame body Problem AnalysisAd hoc 802.11 MACFuture Plans Octets FCS CostSA Sequence Control DATARA Duration / ID Frame Control 426266622

14. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 14/17 Protocol Components  Possible situations for Repair operation  A node receives a data frame addressed to itself with RA as a broadcast address –A path repair frame will be sent  RA in this frame would be broadcast  SA and DA will be copied from the data frame just received  The cost field will carry the SCF value of the data frame just received  A node receives a data frame addressed to itself through a path which has higher cost than a path already known to it –A path repair frame will be sent to SA on the previously (low cost) known path  A node receives a data frame with RA as broadcast –A path repair frame will be sent to TA if DA is known Problem AnalysisAd hoc 802.11 MACFuture Plans

15. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 15/17 Some Results  25 Nodes  10 and 20 Source/Destination pairs  Speed 1 m/sec  Pause Time 0 seconds  4 packets of 1024 bytes per second generated by each source. Max 10000 packets  CBR sources generating UDP packets Problem AnalysisAd hoc 802.11 MACFuture Plans

16. Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman 16/17 Future Work  The initial simulation results show that scalability could be a big challenge  A detailed analysis of network size, mobility, offered load  Detailed analysis of different components and their effects on performance  Comparison with other well known routing protocols  Possibility of different cost metrics Problem AnalysisAd hoc 802.11 MACFuture Plans

17. Institut für Betriebssysteme und Rechnerverbund Technische Universität Braunschweig Thanks for your attention Habib-ur Rehman