Landmark Routing for Large Ad Hoc Wireless Networks
Globecom 2000San Francisco, Nov 30, 2000
Mario Gerla, Xiaoyan Hong and Gary Pei
Computer Science Department
University of California, Los Angeles
http://www.cs.ucla.edu/NRL/wireless/
Ad Hoc vs Cellular Wireless Nets
Multihop (Ad Hoc)
Single Hop (Cellular)
Base BaseBaseBase
Scalability in ad hoc wireless routing
• Scalability to network size– Potentially, thousands of nodes (e.g., battlefield, sensor networks)
• Scalability to mobility– mobility critical in battlefield and vehicular applications
Do Existing Routing Protocols Scale?
• Proactive routing:– Distance Vector based: DBF, DSDV, WIRP
– Link State
Main limitations: routing table O/H; control traffic O/H
• On-demand, reactive routing:– AODV, TORA, DSR, ABR etc
Main limitations: search-flood O/H with high mobility and many short lived flows
Distance Vector
0
5
1
2
4
3
Destination Next Hop Distance
0 2 31 2 2… … …
Routing table at node 5 :
Tables grow linearly with # nodes
Control O/H grows with mobility and size
Link State Routing
• At node 5, based on the link state packet, topology table is constructed:
• Dijkstra’s Algorithm can then be used for the shortest path
0
5
1
2
4
3
{1}
{0,2,3}
{1,4}
{2,4}
{2,3,5}
{1,4,5}
0 1 2 3 4 50 1 1 0 0 0 01 1 1 1 1 0 02 0 1 1 0 1 13 0 1 0 1 1 0
4 0 0 1 1 1 15 0 0 1 0 1 1
0
5
1
2
4
3
query(0)
query(0)
query(0)
query(0)
query(0)
query(0)
query(0)
reply(0)
reply(0)
reply(0)
On-demand Routing
Advantages:– on-demand request & reply
eliminates periodic update O/H (channel O/H)
– routing table size is reduced (it includes only routes in use) (storage O/H)
Limitations:– not scalable with traffic load– mobility may trigger frequent
flood-searches
Hierarchical Routing
• Traditional solution in large scale networks (eg, Internet):
hierarchical routing
• Unfortunately, hierarchical routing implementation problematic in ad hoc nets
• In a mobile ad hoc network the hierarchical addresses must be continuously changed to reflect movements
• Some ad hoc routing schemes recently proposed use an “implicit” hierarchy (eg, Fisheye, Zone routing, etc)
Wireless Hierarchical Routing(addresses change with motion)
5
1
7
6
11
4
23
10
98
Level = 0
(1,1)
(1,2)(1,3)
(1,4) Level = 1
(2,1) (2,3)Level = 2
DestID
1
6
7
(1,2)
(1,4)
(2,3)
Path
5-1
5-1-6
5-7
5-1-6-(1,2)
5-7-(1,4)
5-7-(1,4)-(2,3)
HSR table at node 5
Implicit hierarchical routing: Fisheye State Routing
11
1
2
3
4
5
67
8
9
9
1012
14 1516 17
18 19
20
21
2223
2425
26
27
28
29
30
31
3234
35
36
Hop=1
Hop=2
Hop>2
13
Fisheye Routing
• In Fisheye routing, routing table entries for a given destination are updated (ie, exchanged with the neighbors) with progressively lower frequency as distance to destination increases
• Property 1: the further away the destination, the less accurate the route
• Property 2: as a packet approaches destination, the route becomes progressively more accurate
• Major “scalability” benefit: control traffic O/H is manageable even for very large network size
• Unsolved problems: route table size still grows linearly with network size; out of date routes to remote destinations
Update O/H Reduction in FSR (optional)
0
5
1
2
4
3
0:{1}1:{0,2,3}2:{5,1,4}3:{1,4}4:{5,2,3}5:{2,4}
101122
LST HOP
0:{1}1:{0,2,3}2:{5,1,4}3:{1,4}4:{5,2,3}5:{2,4}
212012
LST HOP
0:{1}1:{0,2,3}2:{5,1,4}3:{1,4}4:{5,2,3}5:{2,4}
221101
LST HOP
Ad Hoc “Group” Hierarchical Solution: Landmark Routing
• Main assumption: nodes move in groups• Three components in LANMAR:• (1) a “local ” proactive routing algorithm that
keeps accurate routes from a source to all destinations within scope N (e.g., Fisheye alg truncated to scope N, Bellman Ford, DSDV, etc)
• (2) a Landmark selection alg for each logical group
• (3) a routing algorithm that maintains accurate routes to landmarks from all mobiles in the field
Logical SubnetLogical Subnet
• Logical subnet: group of nodes with functional affinity with each other (eg, they move together)
• Node logical address = <subnet, host>
Landmark Routing: the Concept
LandmarkLandmark
• A Landmark is elected in each subnet• Every node keeps Fisheye Link State table/routes
to neighbors up to hop distance N• Every node maintains routes to all Landmarks
Landmark Routing (cont’d)
• A packet to local destination is routed directly using Fisheye table based on MAC address
• A packet to remote destination is routed to corresponding Landmark based on logical addr
• Once the packet gets within Landmark scope, the direct route is found in Fisheye tables
• Benefits: dramatic reduction of both routing overhead and table size; scalable to large networks
LandmarkLandmark
Logical SubnetLogical Subnet
Landmark Routing: Dynamic Election
• Dynamic landmark election a must in a mobile environment and in presence of enemy attacks
• Node with largest number of group members in its scope proclaims itself Landmark for group; ties broken by lowest ID
• “Oscillation” of landmark role is eliminated by hysteresis.
• Multiple landmarks may coexist if group spans several “scopes” (they can be hierarchically organized)
Landmark Election (detail - may skip)
• Landmark election algorithm:– No landmark exists initially, only FSR progresses.
– A node proclaims itself as a landmark when it detects > T number of group members in its FSR scope.
– An election is required to select the winner in the group.
• Simple election winner algorithm– A node with the largest number of group members wins and the
lowest ID breaks a tie.
• Hysteresis election winner algorithm– 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.
Drifting nodes (detail - may skip)
• Drifters are nodes outside of the scope of their landmark
• Drifters periodically “register” with Landmark• Registration message creates reverse path from
Landmark to drifter• A packet directed to a drifter must be first
received by the Landmark and then forwarded to drifter
• Routing table entries to drifters increase routing table OH; however, the extra O/H is low if drifter fraction is low
Illustration by Example
A
B
C D
HI
JK L
O
P
LM1
LM2
LM3
LM4
Simulation Environment
• GlomoSim platform• 100 nodes• 1000x1000 square meter simulation area• 150m radio range• UDP sessions between random node pairs• CBR traffic ( one 512 byte pkt every 2.5 sec)• # of logical groups = 4• 2-level Fisheye with radius = 2 hops• IEEE 802.11 MAC layer; 2Mbps link rate• Reference Point Group Mobility model
– random waypoint model is used for both individual and group component of the mobility vector
Throughput and Delay
mobility = 6 m/s
0
200
400
600
800
1000
1200
1400
10 30 50 100 200 300 400 500
number of communication pairs
dela
y (m
sec)
AODV
LANMAR
FSR
mobility = 6 m/s
0
50
100
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300
10 30 50 100 200 300 400 500
number of communication pairs
Thro
ughp
ut (k
bits
/sec
)
AODV
LANMAR
FSR
Routing Load with and w/o Election
Conclusions
• Accuracy of the route to Landmark nodes proves to be adequate
• LANMAR exhibits good scalability with increasing communication pairs
• LANMAR provides a dramatic reduction in routing table storage overhead with respect to FSR
• Dynamic Landmark Election introduces only a moderate increase in routing O/H (with respect to fixed Landmark)
Work in Progress (optional)
• Independent (instead of group) mobility• Very small groups (in the limit, all isolated
nodes)• “Optimal” scope of local routing• Hierarchical Landmark organization• Membership change from one group to
another • Landmarking in a heterogeneous
structure: directive antennas, UAVs etc
The End
Thank You !
www. cs.ucla.edu/NRL