540 likes | 1.04k Views
LANMAR: Landmark Routing for Large Scale Wireless Ad Hoc Networks with Group Mobility. Guangyu Pei, Mario Gerla and Xiaoyan Hong. Outline. Introduction Ad hoc routing Link State Routing Distance Vector Routing Fisheye State Routing LANMAR Routing Drifting and isolated nodes Simulations
E N D
LANMAR: Landmark Routing for Large Scale Wireless Ad Hoc Networks with Group Mobility Guangyu Pei, Mario Gerla and Xiaoyan Hong
Outline • Introduction • Ad hoc routing • Link State Routing • Distance Vector Routing • Fisheye State Routing • LANMAR • Routing • Drifting and isolated nodes • Simulations • Related works • Landmark election • Dynamic group discovery • M-LANMAR • Direction forwarding
Ad-Hoc routing protocol • A wireless network between mobile nodes • No infrastructure • Limited communication distance • Usually low-powered • Mult-hop communication • How to route messages? • Flooding • Simple – keep track of neighbors only • Inefficient use of bandwidth • Not scalable • Along the (shortest) path from source to destination • Requires nodes to keep some topology data
Mobility • Node moves cause network topology changes • Results in routes change • Nodes need to update their topology information • A node (dis)connecting to(from) a neighbor needs to notify other nodes • How to make update process efficient • Low overhead • Fast update propagation
Routing algorithms • Proactive • Constantly monitor network topology • Advantage: Always know how to route to any node (up to mobility) • Disadvantages • Routing table storage • Periodic control traffic overhead (to handle mobility) • Example protocols: LSR, OLSR, DSDV, FSR, LANMAR • Reactive / on-demand • Look for a route only when need to send a packet • Advantages • Low routing table storage (only routes in use) • No periodic control traffic • Disadvantage: route search overhead with high mobility and many short lived flows • Example protocols: AODV, TORA, DSR, ABR
Link State Routing • Similar to existing protocols of Internet routers • Routing table update at each node • Periodically or on link addition/removal: flood “link state” – list of neighbors • Re-broadcasts link state information received from neighbors • Employ “sequence numbers” to distinguish new from stale updates • Each node maintains a routing table with all the “link state” of all the nodes in the system • Routing • The destination is stored in the message header • Each forwarding node finds the shortest path to the destination according to its routing table
1 Link State Routing 0 {1} • At node 5, based on the link state packets, topology table is constructed: • Dijkstra’s algorithm can then be used for the shortest path {0,2,3} {1,4} 3 2 {1,4,5} 4 {2,3,5} 5 {2,4}
Link State Routing drawbacks • As number of nodes grows / mobility increases • Routing tables grow linearly (assuming constant density) • Link state control traffic grow linearly • Not scalable
Distance Vector (DV) Routing • Do not keep the complete links state of node i • Only the next hop neighbor and the distance towards i • Routing is simpler (no need to find a shortest path) • Maintenance • Periodically exchange distance vector (DV) with neighbors • Update own DV if receive a shorter path to i • Problems • Loops • Count to infinity • Scalability – similar to LS
Fisheye State Routing • A variant of Link State routing • Aimed at reducing control traffic (link state updates) • At the expense of routing table accuracy • Which entries in the routing table can be updated less frequently? • The ones corresponding to a more distant nodes
Fisheye State Routing • Maintain accurate information in immediate neighborhood (hop=1) • Progressively less detail as distance increases • Entries of nearby nodes are exchanged more frequently • Frequency decreases proportionally to distance • Topology information is exchanged between neighbors via Unicast • Routing - as packet gets closer to destination, routing accuracy increases
Fisheye State Routing LST HOP 0 LST HOP 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 1 0 1 1 2 2 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 1 2 0 1 2 1 3 Entries in black are exchanged more frequently LST HOP 2 0:{1} 1:{0,2,3} 2:{5,1,4} 3:{1,4} 4:{5,2,3} 5:{2,4} 2 2 1 1 0 1 4 5
FSR – Conclusions • Major scalability benefit: control traffic decreases significantly • Unsolved problems • Route table size still grows linearly with network size • Out of date routes to remote destinations
Logical Group Landmark LANMAR • Define an ad hoc groups of nodes moving together • Fisheye routing inside the group • Other routing algorithms possible • Landmark node elected for each group • Each node maintains • FSR routing table inside its group • Accurate route to all landmarks • Association of each node to its group (landmark)
Routing • Definitions • Logical subnet: a group of nodes moving together • Node logical address: <subnet, host> • Node local scope: a k-hop neighborhood of the node • Routing based on existing routing protocols • FSR routing within local scope • Distance Vector routing to distant nodes via landmarks • Reduction of both control overhead and table size • Scalable to larger networks
Routing tables • A – neighbor list • TT – Fisheye routing table for local scope • j {all the nodes in the scope} • LS(j) – Link state of node j • SEQ(j) – Link state timestamp of node j • NEXT – next hop table • j {all the nodes in the scope} {all the landmarks} • NEXT(j) – the next hop along shortest path • D – distance table • j {all the nodes in the scope} {all the landmarks} • D(j) – shortest path length to j • Other distance functions possible (e.g., bandwidth)
Routing algorithm • If the destination in the scope • route by TT • Else • Set landmark = a landmark node in the subnet of the destination • Route towards landmark by NEXT • Packets do not need to pass through the landmark • Once reached the scope of the destination, routed directly via Fisheye tables (TT) • Do not overload landmark
Updating routing tables • Similar to FSR - periodically exchange scope topology with neighbors • Assume all the subnet is within the scope of its landmark • Piggy-back landmark distance vector • No details in the paper on NEXT and D maintenance
Landmarks • Landmark election not described in the paper • Assume some additional algorithm • No support for moving between groups/landmarks • Would require changing subnet – effectively a new node
Routing table storage • 100 nodes, 4 groups • FSR: 2600 bytes per node • LANMAR: 690 bytes per node • N nodes, N subnets, N nodes in scope • FSR: O(N) per node • LANMAR: O(N) • Also decreases control traffic, power consumption
Drifter nodes • Assume most of the subnet is within the scope of its landmark • Few nodes may move out of the scope • The landmark L needs to know a path to a “drifter” k • Modify the routing protocol • Each node i, on the shortest path between L and k, keeps a DV entry to k • If k is within the scope of i, it is already in i’s Fisheye table • When i transmit its DV to j (in the same subnet), j keeps k’s entry iff • d(j,l) < scope OR d(j,L) < d(i,L) • Landmark has a path to all drifters • For 20% of drifter nodes ~7% extra overhead (in some specific setting)
Isolated nodes • Nodes in groups of size 1 • If such nodes are rare – consider them landmarks • If many isolated nodes – need different protocols • Hybrid protocol • Consider isolated nodes landmarks • Lower DV update frequency with distance increase • Gradual transition from LANMAR to FSR performance • On-demand routing to isolated nodes • Associate each isolated node with Home Agent • Home Agent constantly maintains a route to a node
Simulations • Setup • 1000 x 1000 meters square • 150 meter range • 2 Mbit/sec channel capacity • 100 nodes, 4 groups • Scope = 2 hops • Source-destination pairs chosen randomly • UDP messages – 512 bytes, sent every 2.5 seconds • Reference Point Group Mobility • Two components – individual and group • Each based on a random waypoint model • Speed - 2 to 10 m/s
Performance metrics • Routing effectiveness metrics • Packet delivery fraction • Average end-to-end packet delay • Not independent – dropped packets not included in delay computation • Normalized routing load • Number of control packet per delivered data packet • Throughput – the actual throughput at destination
Delivery fraction • Only 10 pairs communicate • On-demand protocol(AODV) performs best • LANMAR outperforms FSR as speed increases • Better to have accurate routes to few landmarks that inaccurate ones to all distant nodes
Delivery fraction • 300 pairs communicate • On-demand protocols underperform due to control traffic lost to buffer overflows • FSR and LANMAR nearly unchanged • LANMAR outperforms all other protocols beyond 30 pairs
Delay • As load increases delay increases due to queue buildup • LANMAR performs best due to low control overhead
Routing overhead • For FSR and LANMAR the overhead is constant • Normalized load (overhead per delivered packet) rises as delivery fraction falls • On-demand protocols’ load increases sharply with traffic
Throughput • Throughput grows with load until the network saturates • Depends also on delivery fraction • AODV saturates first, due to high routing overhead • LANMAR outperforms other protocols
Conclusions • LANMAR improvements over FSR • Lower storage and traffic overheads • Better performance under high load/mobility • Assumption: nodes move in groups • Instead of handling each distant node individually, handle as a group • Need additional algorithm for landmark election • Yet another hierarchical protocol (ZRP, HSR, CGSR) • Not really scalable – one level of hierarchy • Non-adaptive groups/FSR scopes • √N group/scope size analysis does not hold for dynamic joins/leaves
Landmark electiondraft-ietf-manet-lanmar-03.txt • Landmark election algorithm: • No landmark exists initially, only FSR progresses • A node proclaims itself as a landmark when it detects more than T group members in its FSR scope • An election is required to select the winner in the group • Election algorithm • A node with the largest number of group members wins and the lowest ID breaks a tie • To prevent frequent landmark change • The current election winner replaces the old landmark when its number of group members is larger than the old one by an extra fraction • Or, the old landmark gives up the landmark role when its number of group members reduces to a value smaller than a threshold T
Dynamic group discovery"Dynamic Group Discovery and Routing in Ad Hoc Networks", X. Hong and M. Gerla • Groups are not known in advance • Location and speed not required (no GPS) • Each node finds its Traveling Companions (TCs) • By inspecting FSR tables for some time window W • Leader (landmark) election • Node’s “weight” is the number of its TCs • Each node broadcasts it weight to its group • Node with highest weight is elected • Leader’s ID become the subnet ID • Works only initially, group changes require more work
M-LANMAR “Scalable team multicast in wireless ad hoc networks exploiting coordinated motion”, Y. Yi, M. Gerla, K. Obraczka
M-LANMAR • Multicast: transmit the same packet to multiple destinations • Unicast to each destination is inefficient - wastes network bandwidth • Intra – group multicast: • Sensor data “fusing” • Inter – group multicasting: • “fused” video/image/data is multicast to other groups
M-LANMAR • Based on LANMAR • Nodes move in groups • Landmark is elected in each group • Multicast LANMAR (M-LANMAR) • Unicast tunneling from the source to the Landmark of each “subscribed” group • Scoped flooding within a group
Scope = 2 Flooding Tunneling Scope = 2 Flooding LM2 LM1 LM3 Subscribed Teams Source node LM4
DFR “Direction” Forward Routing for Highly Mobile Ad Hoc Networks, YZ Lee, M Gerla, J Chen, J Chen, B Zhou, A Caruso
DV • In DV routing, node keeps pointer to successor to destination Route update Successor Data flow Source Sink • When the successor moves, the path is broken • Alternate paths, even when available, are not used • Solution: direction forwarding
Direction Forwarding • Routing update creates not only “successor”, but also “direction” entry Route update Successor Data flow Source Sink “Direction” to Sink • Select “most productive” neighbor in forward direction • If the network is reasonably dense, the path is salvaged
How to compute the “direction”? • Need “stable” local orientation system (e.g., virtual compass) to determine direction of update • GPS will do, but it is an overkill (global orientation) • Several non-GPS local coordinate systems have been proposed • Sextant [Mobihoc ’05]; beacon DV • Local reference system must be refreshed fast enough to track average local motion
Computing the “direction” • Compute “direction” to a destination when the routing updates are received • The “direction” to the upstream neighbor is used as the “direction” to the destination • If multiple updates received from different neighbors with same hop distance • Take vector sum of directions
“Direction” to a destination C A B Computing the “direction” • Node A receives DV update packets from B & C • Compute the “directions” to node B & C, respectively, Directions to neighbors Computation of the “direction” • Unit vectors are used to combine the two “directions”
Delivery fraction increases DFR LANMAR Delivery ratio vs. speed (Excluding packet loss due to disconnected destination)
DFR Conclusions • DFR: new forwarding strategy for table driven routing • Direction Forwarding can improve traditional routing performance dramatically in high speed • DFR is about as robust as geo-routing • Yet DFR does not suffer the limitations of geo routing: • GLS • Global GPS required at all mobiles • Possible dead-end ineffciencies