1. Dissertation Defense
On-Demand Link-State Routing in
Ad-Hoc Networks
Soumya Roy
Computer Engineering,
University Of California, Santa Cruz
Adviser : Prof. JJ Garcia Luna Aceves

2. Presentation Outline
 Wireless ad-hoc networks
 On-demand link-state routing protocol
 Source-tree On-demand Adaptive Routing
protocol (SOAR)
 Path Selection
 On-demand Link Vector Protocol (OLIVE)
 Node-centric hybrid routing approach for
practical scenarios of ad-hoc networks

3. PART ONE
Wireless Ad Hoc
Networks

4. Wireless Ad Hoc Networks
WLAN Ad hoc Networks
Nodes acts as sources, relays and destinations of data packets
Routing protocol is needed for data delivery

5. Challenges in Designing Routing
Protocols for Mobile Ad-Hoc Networks
 Significant Packet Loss :
 Fading, interference, collisions
 Less bandwidth than wired networks
 Network Topology highly dynamic
because of router or host mobility
 Routing protocols should adapt fast to
link failures and converge fast
 Routing overhead should be minimal

6. Taxonomy of Routing Protocols
 Proactive Routing (WRP, DSDV, OLSR,
STAR)
 Maintains routes for all destinations
 Redundant routes
 Reactive Routing (AODV, DSR, DST)
 Maintains routes for necessary nodes
 Uses flooding of requests to discover paths
 Long delays for path set up

7. Main goal is to ….
Explore how link-state information can be
used efficiently for setting up
on-demand routes

8. Previous Work
 Proactive link-state protocols
 Source Tree Adaptive Routing (STAR)

Exchanges source trees
 Topology Broadcast based on Reverse-Path
Forwarding (TBRPF)

Exchanges reportable part of source tree
 Optimized Link-State Routing (OLSR)

Uses multipoint relays to prevent flooding
 Performance good compared to on-demand
routing protocols using routing information in
other forms

9. PART TWO
On-Demand Link-
State Routing

10. Outline
 Source Tree On-demand Adaptive
Routing (SOAR)
 Challenges in the path selection
 On-demand Link Vector Routing
(OLIVE)

11. Source Tree On-demand Adaptive
Routing (SOAR)

12. What is Source Tree
 Each node can build source tree based
on paths to all reachable destinations
a
b c
SOAR exchanges minimal source trees
d e f
g h i j k
l m
Source Tree at node a

13. What is a Minimal Source Tree
 Contains paths to important nodes
(relays, potential relays, receivers)
a a
b b c
c
d e f d e f
jj g jj
g h i k
Minimal Source Tree
l m l
reported by node a
Source Tree at a

14. Construction of Topology Table
i
x a a x
i y c i c y
+ =
Minimal source tree Minimal source tree Partial topology at i
of x of a
 Modified Bellman-Ford Algorithm used
for path selection

15. Summary
 Query, Reply for path discovery
 Updates for path repair
 ForcedUpdate, ForcedReply for forcing
nodes adopt shortest paths
 Links validated using sequence number
 Data packets contain traversed paths

16. Performance Evaluation (ns2)
 20 nodes
 1000mx300m rectangular field
 IEEE 802.11 MAC
 Link layer notification of link failures
 Re-routing of data packets possible in
case of link breakage
 Comparisons with DSR and AODV

17. Effect of Increasing Flows (pause=0s)

18. Effect of Mobility (10 flows)

19. Effect of Loading (10 flows)

20. Challenges of Path Selection in On-
demand Link State Routing

21. Path Selection Algorithm
Links advertised by b
(c) (c)
c d f Links advertised by c
(c)
(c) (c)
a (b) (c)
g
(b) h
(b) e
b
 Path through a neighbor valid if later has
advertised it
 Choose the shortest among the valid options

22. Computing Source Tree
OPT-TREE : Given a graph and a set of
labels corresponding to each link, what
is maximum size of the source tree that
can be built while satisfying the rules of
shortest path and on-demand route
advertisement?
NP complete problem (reduction of
3SAT problem to a graph)

23. Computing Source Tree (contd…)

24. Heuristic for Computing Source Tree
 A polynomial time approximation (O(nd^2))
algorithm
 Finding shortest valid paths for a destination
and combining those paths
 Local maxima instead of global maxima
 Disadvantage: computing source tree not an
efficient usage of routing information
 A mechanism for policy-based routing

25. Computing source graph (in SOAR)
MBF BF
(a,d1) (x,d2)
j d1 >d2
(x,d2)
i
i i
k (a,d1+1)(x,inf) (x, d2+1)
a x a x a x
d1 d2
j (j,k) link has been j j
advertised by x only
k k k
Partial topology at i
Source Graph at i Advertised
Source Tree at i

26. How does SOAR handle path
selection problem
 Computes source graph
 Exchanges source trees
 Uses forced routing to convert source
graphs to trees
 Disadvantage:
 Loops can form
 Extra overhead of forced routing

27. Next Step …….
 Use of complete path information
 Links in paths validated using sequence
numbers
 Links merged to help in local route
repair and limited route requests
 Instantaneous loops to be prevented
without any control overhead in data
packets or any global synchronization

28. On-Demand Link Vector Protocol
(OLIVE)

29. Overview of OLIVE
 Route discovery
 Setting up new paths
 RREQ, RREP and RREPACK
 Route Repair
 Locally repair routes or limit route searches
 FRREQ, FRREP
 Route Failure Notification
 To notify route failures
 RERR, RERRACK

30. Use of path information in OLIVE

31. Use of path information (contd …)
c e

32. RREQ
d
a
RR
EQ
RREQ
i
j
k
RR
EQ c
b
RREQ
RREPACK
RREP
a
d
RR
EP
RREP
Example (Route Discovery)
i
j
k
RR
RREPACK PE
RR AC
b
K
c
EP
RREP
RREPACK

33. Example (Route Error and Repair)
j
j
d c
d c
RREQ
FRREQ
RREQ
FRREP
a b
a b
FR
EQ
RR
FR
RE
RERRACK
RR
EQ
RE
P
k
RERR
k
Q
i RREQ i

34. Properties of OLIVE
 When cost of path can increase, inter-
neighbor synchronization is used
 Predecessors release the successor
 Loop-free paths set up when all
predecessors release
 Every node knows correctly at every
instance its set of predecessors
 Data packets from unknown
predecessors always dropped

35. Performance Evaluation (ns2)
 50 nodes
 1500x300m (range = 250m)
 2Mbps DSSS radio interface
 Random Waypoint model
 IEEE 802.11
 Compared with DSR, OLSR, TBRPF,
AODV

36. Simulation Results (10 flows)
Percentage Throughput Total Control Packets

37. Simulation Results (10 flows)
Optimality of routes End to end delay

38. Effect of Packet Load (20 sources)
Control packets sent Percentage Delivery

39. Effect of Packet Load (20 sources)
Optimality of routes End-to-end Delay

40. Quantifying loops
Packet rate = 8 packets/s Packet rate = 10 packets/s

41. Summary
 Elaborately studied the problem of
using on-demand link-state information
for routing
 Developed routing solutions that give
better performance than existing
popular routing protocols
 OLIVE can be very good choice for use
in ad hoc networks

42. PART 2
Node-Centric Hybrid Routing for
Ad Hoc Networks

43. Outline
 Introduction
 Reasons behind node-centric hybrid
routing
 Methods and new protocols
 Performance evaluation

44. Introduction
 Practical scenarios for mobile ad-hoc
networks will have traffic between
mobile nodes and netmarks
 Where can we see such scenarios :
 Internet Access Points
 Hosts for DNS services
 Web Proxies
 Group leaders
 Cluster-heads for hierarchical routing

45. Practical Ad Hoc Networks

46. Related Work in Hybrid Routing
 Zone Routing Protocol (Haas & Pearlman)
 Proactive routing within zones
 Reactive routing between zones
 Landmark Hierarchy (P.F. Tshuchiya)
 Node centric approach to hierarchical
routing for proactive routing
 Landmark’s address: address for common
node
 Our approach: Type of routing is based
on nodes and not on zones or areas

47. Why Node-centric Hybrid Routing
 On Demand path creation towards netmarks
 Each session set up leads to flooding, delay
 Intuitively not best approach if the netmark is
communicated frequently though not continuously
 Maintaining pro-active routes
 High control overhead
 Redundant paths as peer-to-peer communication is
much less compared to number of nodes
 Node-centric hybrid routing: a tradeoff
 Proactive routes towards netmarks
 On demand path creation among mobile nodes

48. Methods of Node-Centric Hybrid
Routing
 Prolonged Caching
 Caching of netmark information for long
enough periods
 Proactive routes
 Proactive routing for the netmark so that
paths towards netmarks remain always
updated while paths between mobile nodes
are set up on-demand

49. Protocols with Prolonged Caching
 Route errors and route requests for netmarks
do not depend on traffic
 AODV : longer routing entry timeout for
netmarks
 DSR : advantage not realizable since routing
solely controlled by traffic
 SOAR :Netmarks will be important for longer
time interval, hence caches/maintains
netmark path information for longer periods

50. Protocols With Proactive Netmark Routes
1. Nemarks advertise their presence
 MAC layer sends beacons
 Routing Layer sends Hellos
2. Route errors and route requests for
netmarks do not depend on traffic
 Changes 1 and 2 can be easily made
for DSR, SOAR and AODV

51. Protocols with Proactive Routes
(contd…)
3. New paths to netmarks are always
advertised
 Change 3 needs modifications
 SOAR sends updates immediately on
discovering new routes
 AODV and DSR need new type of control
packets for proactive route set up

52. SOAR with Hybrid Functionality
 SOAR performs better than both DSR or AODV
 Modifications of SOAR to incorporate hybrid
routing simpler than in DSR or AODV
 Netmark Aware On Demand Link-State Routing
(NOLR) : extended caching of netmarks
 Netmark-Enhanced Source Tree Routing
(NEST) : proactive routes for netmarks

53. Setting up paths in NEST
 Forward paths are set up proactively
Reverse paths are set up by traffic flows (soft state or
on-demand) (e,b)
hel (e,a)
lo n
n
lo
n
hel
b b b
(e,d)
update
a a (e,c) a
(e,c)
update d
upd
(e,e) d d
(e,e)
at e
c c c
update
e e e

54. Issues in Hybrid Routing
 Forwarding of data packets
 Use of subnet address for ad hoc networks
 Multiple Netmarks
 Load balancing
 Complexity in packet forwarding (static, dynamic,
hybrid affiliations)
 Asymmetry in paths
 Change in query mechanism (anycast queries)

55. Performance Evaluation
 Using ns2
 Comparison of NEST, NOLR with DSR,
AODV and SOAR

56. Traffic and Mobility Models
 Mobility Model : random waypoint model
 Traffic Pattern
 FLOW OFF/ON model
 Data Traffic and Voice traffic Simulation

57. Simulation Scenario 1
 31 nodes
 single netmark in the centre of a
rectangular field
 (1000m x 500m) size
 Range = 250m
 Simulation length : 600 secs
 load = 3 packets/sec 5 packets/sec
 Speed : 5m/s-20m/s

58. Performance Evaluation (3 pkts/s)
Percentage Throughput
Control packet

59. Performance Evaluation (5 pkts/s)
Control packets Percentage Throughput

60. Simulation Scenario 2
 31 nodes
 single netmark
 Static
 Mobile in a restricted region
 Mobile throughout the rectangular field
 Traffic flows ( 2 models)
 6 random flows among netmark and mobile nodes
(battlefield or relief)
 Any mobile node can talk to netmark (Internet)

61. Performance Evaluation

62. Simulation Scenario 3
 31 nodes
 Two static netmarks
 To observe : can anycast route
discovery lead to any significant
improvement

63. NEST
A-SOAR
NOLR
Performance Evaluation

64. Contributions
 First detailed study on use of link-state
information on-demand
 Developed two unique highly efficient
routing protocols
 Demonstrated the complexity of path
selection in on-demand routing
 Presented a new genre of hybrid
routing targeting practical ad-hoc
networks

65. Future Work
 Opportunistic version of OLIVE to target
practical ad-hoc networks
 Node-centric version targeting huge
networks without added complexity of
hierarchy management
 Modeling ad-hoc networks based on
parameters like node density

66. Acknowledgements
 Thanks to JJ for being the greatest adviser
 Thanks to Richard, Katia for being on my
defense committee, and Suresh for being on
my advancement committee.
 Thanks to my parents and brother who have
always supported me
 Thanks to my friends in Baskin Engineering,
Bay Area and CCRG for all the help during
my PhD life

67. THE END

68. Publications
 SOAR (IEEE Infocom 2001)
 Heuristic for Source Tree Computation
(ICCCN 2002)
 Node-Centric Hybrid Routing
(Globecom 2002, Mascots 2002, Book
Chapter)
 Path Selection problem (submitted to
PODC 2003)
 OLIVE (Mobicom 2003)

69. Pending publications

70. Simulation Results (10 flows)
Total Control Bytes Total MAC layer packets