05 MANETs BÀI GIẢNG MẠNG MÁY TÍNH NÂNG CAO

Mobile Ad Hoc Networks g  g  g  Formed by wireless hosts which may be mobile Without (necessarily) using a pre-existing infrastructure Routes between nodes may potentially contain multiple hops Mobile Ad Hoc Networks g  May need to traverse multiple links to reach a destination Mobile Ad Hoc Networks (MANET) g  Mobility causes route changes Why Ad Hoc Networks ? g  Ease of deployment g  Speed of deployment g  Decreased dependence on infrastructure Many Applications g  g  g  g  Personal area networking icell phone, laptop, ear phone, wrist watch Military environments isoldiers, tanks, planes Civilian environments i taxi cab network imeeting rooms isports stadiums i boats, small aircraft Emergency operations isearch-and-rescue i policing and fire fighting Many Variations g  g  Asymmetric Capabilities i transmission ranges and radios may differ i battery life at different nodes may differ i processing capacity may be different at different nodes ispeed of movement Asymmetric Responsibilities i only some nodes may route packets isome nodes may act as leaders of nearby nodes (e.g., cluster head) Many Variations g  Traffic characteristics may differ in different ad hoc networks i bit rate i timeliness constraints ireliability requirements i unicast / multicast / geocast i host-based addressing / content-based addressing / capability-based addressing g  May co-exist (and co-operate) with an infrastructurebased network Many Variations g  g  Mobility patterns may be different i people sitting at an airport lounge i New York taxi cabs ikids playing imilitary movements i personal area network Mobility characteristics ispeed i predictability • direction of movement • pattern of movement i uniformity (or lack thereof) of mobility characteristics among different nodes Challenges g  g  g  g  g  g  g  g  Limited wireless transmission range Broadcast nature of the wireless medium i Hidden terminal problem (see next slide) Packet losses due to transmission errors Mobility-induced route changes Mobility-induced packet losses Battery constraints Potentially frequent network partitions Ease of snooping on wireless transmissions (security hazard) Hidden Terminal Problem A B C Nodes A and C cannot hear each other Transmissions by nodes A and C can collide at node B Nodes A and C are hidden from each other 10 Merging Partitions: AODV P A B RREQ (repair) Q 169 Merging Partitions: AODV P Group Hello (update) A B Q Q becomes leader of the merged multicast tree New group sequence number is larger than most recent ones known to P and Q both 170 Summary: Multicast AODV g  g  Similar to unicast AODV Uses leaders to maintain group sequence numbers, and to help in tree maintenance 171 On-Demand Multicast Routing Protocol (ODMRP) g  g  ODMRP requires cooperation of nodes wishing to send data to the multicast group i To construct the multicast mesh A sender node wishing to send multicast packets periodically floods a Join Data packet throughout the network iPeriodic transmissions are used to update the routes 172 On-Demand Multicast Routing Protocol (ODMRP) g  Each multicast group member on receiving a Join Data, broadcasts a Join Table to all its neighbors iJoin Table contains (sender S, next node N) pairs i next node N denotes the next node on the path from the group member to the multicast sender S g  g  When node N receives the above broadcast, N becomes member of the forwarding group When node N becomes a forwarding group member, it transmits Join Table containing the entry (S,M) where M is the next hop towards node S 173 On-Demand Multicast Routing Protocol (ODMRP) g  Assume that S is a sender node S N M A D C B Join Data T Multicast group member 174 On-Demand Multicast Routing Protocol (ODMRP) N S M Join Data A Join Data Join Data T D Multicast group member C B 175 On-Demand Multicast Routing Protocol (ODMRP) S N M A Join Table (S,M) T D C B Join Table (S,C) Multicast group member 176 On-Demand Multicast Routing Protocol (ODMRP) Join Table (S,N) S T F N M A D F C B Join Table (S,N) F marks a forwarding group member 177 On-Demand Multicast Routing Protocol (ODMRP) Join Table (S,S) N S F M A F C B F T D Multicast group member 178 On-Demand Multicast Routing Protocol (ODMRP) F S N M A F C B F T D Join Data (T) Multicast group member 179 On-Demand Multicast Routing Protocol (ODMRP) F S N F M A Join Table (T,C) F F C B T D Join Table (T,T) Join Table (T,D) Join Table (T,C) Multicast group member 180 ODMRP Multicast Delivery g  A sender broadcasts data packets to all its neighbors g  Members of the forwarding group forward the packets g  Using ODMRP, multiple routes from a sender to a multicast receiver may exist due to the mesh structure created by the forwarding group members 181 ODMRP g  g  g  g  g  No explicit join or leave procedure A sender wishing to stop multicasting data simply stops sending Join Data messages A multicast group member wishing to leave the group stops sending Join Table messages A forwarding node ceases its forwarding status unless refreshed by receipt of a Join Table message Link failure/repair taken into account when updating routes in response to periodic Join Data floods from the senders 182 Open Problems g  Issues other than routing have received much less attention so far Other interesting problems: g  g  g  g  g  g  Address assignment problem MAC protocols Improving interaction between protocol layers Distributed algorithms for MANET QoS issues Applications for MANET 183