Ad Hoc Routing

1
Ad Hoc Routing

• CS 218 Fall 2008
• Mario Gerla
• Computer Science Dept
• UCLA

2
Outline

• Conventional wired-type schemes (global routing,
  proactive)
• Distance Vector Link State
• Why they do not work in ad hoc networks
• Proactive ad hoc routing
• OLSR Hierarchical Fisheye OLSR Fisheye
• On- Demand, reactive routing
• AODV (Backward learning0
• DSR (Source routing)
• AODV DFR
• A hybrid scheme
• ---------------------------------------- next
  week Monday --------------------------------
• Geo-routing
• Multicast

3
Readings

• Thomas Clausen, Philippe Jacquet, " Optimized
  Link State Routing Protocol (OLSR) ," IETF
  Internet Draft , July 3 2003.
• X. Hong, K. Xu, and M. Gerla, " Scalable Routing
  Protocols for Mobile Ad Hoc Networks " IEEE
  Network Magazine, July-Aug, 2002, pp. 11-21
• G. Pei, M. Gerla, and X. Hong, " LANMAR Landmark
  Routing for Large Scale Wireless Ad Hoc Networks
  with Group Mobility," In Proceedings of IEEE/ACM
  MobiHOC 2000, Boston, MA, Aug. 2000.

4
Wireless multihop routing challenges

• mobility
• need to scale to large numbers (100s to 1000's)
• unreliable radio channel (fading, external
  interference, etc)
• limited bandwidth
• limited power
• need to support multimedia applications (QoS)

5
Conventional wired routing limitations

• Distance Vector (eg, Bellman-Ford, DSDV)
• routing control O/H linearly increasing with net
  size
• convergence problems (count to infinity)
  potential loops
• Link State (eg, OSPF)
• link update flooding O/H caused by frequent
  topology changes
• Note These schemes are known as proactive,
  since they compute routes ahead of time, in the
  background
• In contrast, on demand schemes compute routes
  only as needed
• CONVENTIONAL ROUTING DOES NOT SCALE TO SIZE AND
  MOBILITY

6
Distance Vector
0
Routing table at node 5
1
3
2
4
Tables grow linearly with nodes Control O/H
grows with mobility and size
5
7
Link State Routing

• At node 5, based on the link state pkts, topology
  table is constructed
• Dijkstras Algorithm can then be used for the
  shortest path

0
1
0,2,3
1,4
3
2
1,4,5
4
2,3,5
5
2,4
8
Outline

• Conventional wired-type schemes (global routing,
  proactive)
• Distance Vector Link State
• Why they do not work in ad hoc networks
• Proactive ad hoc routing
• OLSR,
• Hierarchical
• Fisheye
• OLSR Fisheye
• On- Demand, reactive routing
• AODV (Backward learning0
• DSR (Source routing)

9
Proactive ad hoc schemes OLSR and TBRPF

• Distance Vector inadequate - used only for very
  small nets
• Link State explodes because of Link State update
  overhead
• Question how can we reduce the O/H?
• Answer Link State with Topology reduction
• (1) if the network is dense, use fewer
  forwarding nodes
• (2) if the network is dense, advertise only a
  subset of the links
• Two leading IETF MANET Link State schemes enhance
  scalability in large scale networks
• OLSR Optimal Link State Routing
• TBRPF Topology Broadcast Reverse Path Routing

10
OLSR Overview

• In LSR protocol a lot of control messages
  unnecessarily duplicated
• In OLSR only a subset of neighbors (Multipoint
  Relay Selectors) retransmit control messages
• Reduce flooding overhead
• OLSR retains all the advantages of LSR
• stable
• Does not depend upon any central entity
• Tolerates loss of control messages
• Supports nodes mobility.

11
Multipoint Relays (MPR)

• Goal reduce duplicate LS (Link State)
  retransmissions
• Each node chooses a set of nodes (MPR Selectors)
  in the neighborhood, which will retransmit its
  LS packets.
• The other nodes receive and process the packet,
  but do not retransmit it

• MPR Selectors of node N - MPR(N)
• - one-hop neighbors of N
• - Set of MPRs is able to transmit to all
• two-hop neighbors
• Link between node and its MPR is bidirectional.

12
Optimized Link state routing (OLSR)
13
Multipoint Relays (MPR) cont.

• Every node keeps a table of routes to all known
  destination through its MPR nodes
• Every node periodically broadcasts list of its
  MPR Selectors (Reduced Link State list)
• Upon receipt of MPR information each node
  recalculates and updates routes to each known
  destination
• Route is a sequence of hops through MPRs from
  source to destination
• All the routes are bidirectional

14
Neighbor sensing

• Each node periodically broadcasts Hello message
• List of neighbors with bidirectional link
• List of other known neighbors. (If node sees
  itself in this list it adds the sender to
  neighbors with bidirectional link)
• Hello messages permit each node to learn topology
  up to 2 hops
• Based on Hello messages each node selects its set
  of MPRs

15
Example of neighbor table
Two-hop neighbors
One-hop neighbors
Also every entry in the table has a timestamp,
after which the entry in not valid
16
MPR Selection

• MPR set need not to be optimal
• hard problem to find an optimal set
• Greedy heuristic
• select node with best 2-hop cover increment
• MPR is recalculated after a change in one-hop or
  two-hops neighborhood topology

17
Conclusions

• OLSR is a proactive protocol
• Suitable for applications which do not tolerate
  large time delays
• Adapted for dense network (reduces control
  traffic overhead)

18
Where do we stand?

• OLSR and TBRPF can dramatically reduce the
  state sent out on update messages
• They effective reduce the working topology in
  dense networks.
• However, the state still grows with O(N)
• Neither of the above schemes can handle large
  scale nets from 10s to thousands of nodes
• What to do?

19
Fisheye State Routing

• Topology data base at each node
  - similar to link state
  (e.g., OLSR)
• Routing update frequency decreases with distance
  to destination
• Higher frequency updates within a close zone and
  lower frequency updates to a remote zone
• Highly accurate routing information about the
  immediate neighborhood of a node progressively
  less detail for areas further away from the node

20
Scope of Fisheye
21
Message Reduction in FSR
LST
HOP
0
LST
HOP
01 10,2,3 25,1,4 31,4 45,2,3 52,4

1 0 1 1 2 2
01 10,2,3 25,1,4 31,4 45,2,3 52,4

2 1 2 0 1 2
1
3
LST
HOP
2
01 10,2,3 25,1,4 31,4 45,2,3 52,4

2 2 1 1 0 1
4
5
22
Optimized Fisheye Link State Routing (OFLSR)

• Based on Optimized Link State Routing (OLSR)
• Borrows idea from Fisheye State Routing (FSR)
• Different frequencies for propagating the
  Topology Control (TC) message of OLSR to
  different scopes (e.g. different hops away)

23
Scalability Property of OFLSR

• Throughput vs Node Mobility
• 100 nodes, 1600mX1600m field, 367m Tx range
• IEEE 802.11 radio, 2Mbps channel rate, 10 CBR
  flows
• OLSR configuration hello interval 1s, TC
  interval 2s
• OFLSR configuration 4 scopes, each scope is 2
  hops except last one

Data Packet Delivery Ratio
Node mobility speed (m/s)
24
Scalability Property of OFLSR

• Scalability to Node Mobility

Total of TC relayed
Total of TC received
25
Scalability Property of OFLSR

• Scalability to Network Size
• Keep node density, increase of nodes, no
  mobility
• OLSR configuration hello interval 2S, TC
  interval 4S
• OFLSR configuration 4 scopes, each scope is 2
  hops except last one

Data Packet Delivery Ratio
Network Size ( of nodes)
Delivery rate vs Network Size
26
Scalability Property of OFLSR

• Scalability to Network Size

Total of TC relayed
Total of TC received
27
Hierarchical Routing

• The previous schemes reduce control traffic O/H
  but do not significantly reduce routing table
  size
• Solution use hierarchical routing to reduce
  table size
• In the process, reduce also control traffic O/H
• Proposed hierarchical schemes include
• Hierarchical State Routing
• Zone routing (hybrid scheme)
• Landmark Routing

28
Hierarchical State Routing (HSR)

• Loose hierarchical routing in Internet
• Main challenge in ad hoc nets maintain/update
  the hierarchical partitions in the face of
  mobility
• Solution distinguish between physical
  partitions and logical grouping
• physical partitions are based on geographical
  proximity
• logical grouping is based on functional affinity
  between nodes (e.g., tanks of same battalion,
  students of same class)
• Physical partitions enable reduction of routing
  overhead
• Logical groupings enable efficient location
  management strategies using Home Agent concepts

29
HSR - physical multilevel partitions
HSR table at node 5
DestID 1 6 7 lt1-2-gt lt1-4-gt lt3--gt
Path 5-1 5-1-6 5-7 5-1-6 5-7 5-7
HID(5) lt1-1-5gt HID(6) lt3-2-6gt
Hierarchical addresses
(MAC addresses)
30
HSR - logical partitions and location management

• Logical (IP like) type address ltsubnet,hostgt
• Each subnet corresponds to a particular user
  group (e.g., tank battalion in the battlefield,
  search team in a search and rescue operation,
  etc)
• logical subnet spans several physical clusters
• Nodes in same subnet tend to have common mobility
  characteristic (i.e., locality)
• logical address is totally distinct from MAC
  address

31
HSR - logical partitions and location management
(contd)

• Each subnetwork has at least one Home Agent to
  manage membership
• Each member of the subnet registers its own
  hierarchical address with Home Agent
• periodical/event driven registration stale
  addresses are timed out by Home Agent
• Home Agent hierarchical addresses propagated via
  routing tables or queried at a Name Server
• After the source learns the destinations
  hierarchical address, it uses it in future
  packets
• Example Landmark Routing

32
Scalable Ad Hoc Routing using Landmarks and
BackbonesCS 218 F 2007
33
The challenge

• Tens of thousands of nodes
• Nodes move in various patterns
• QoS communications requirements
• Hostile environment jamming

34
Routing

• Current MANET solutions have limitations
• (a) proactive routing solutions (eg, Optimal
  Links State -OLSR) do not scale because of table
  size and control traffic overhead
• (b) on demand routing cannot handle high mobility
  and dense traffic patterns
• (c) explicit hierarchical routing introduces
  excessive address maintenance O/H in high
  mobility
• MANET protocols do not scale
• Our approach
• Exploit implicit hierarchy induced by group
  mobility

35
Solution Landmark Routing Overlay

• Main assumption nodes move in groups

• Groups are predefined or dynamically recognized
• Node address lt group ID , Host addressgt
• Landmark elected in each group
• Landmarks advertisements maintain the landmark
  overlay

36
LANMAR Overlay Routing (cont)

• Builds upon existing MANET protocols
• (1) local routing algorithm that keeps
  accurate routes within local scope lt k hops
  (e.g., OLSR)
• (2) Landmark routes advertised to all mobiles
  using DSDV

37
Landmark Routing In action (cont)

• Packet Forwarding
• A packet to local destination is routed
  directly using local tables
• A packet to remote destination is routed to
  Landmark corresponding to logical addr.
• Once the landmark is in sight, the direct route
  to destination is found in local tables.
• Benefits low storage, low update traffic O/H

38
Link Overhead of LANMAR

• Dramatic O/H reduction from linear to O(N) to O
  (sqrtN)

39
LANMAR Local Scope Optimization

• Goal find local routing scope size that
  minimizes routing overhead
• size of landmark distance vector O ( N / G)
• size of local Link State topology map O ( m d
  )
• N total of nodes d avg of
  one-hop neighbors (degree)

H (Routing overhead)
Total O/H
Local route O/H
Landmark O/H
h (scope size)
40
Dynamic Group Formation
41
LANMAR enhances MANET routing schemes

• We compare
• (a) MANET routing schemes DSDV, OLSR and FSR
  and
• (b) same MANET schemes, BUT with LANMAR overlay
  on top

42
Delivery Ratio

• DSDV and FSR decrease quickly when number of
  nodes increases
• OLSR generates excessive control packets, cannot
  exceed 400 nodes

43
Mobile Backbone Overlay

• Landmark Overlay provides routing scalability
• However the network is still flat - paths have
  many hops ? poor TCP and QoS performance!!
• Solution Mobile Backbone Overlay
• MBO is a physical overlay ie long links
• MBO provides performance scalability
• LANMAR extends transparently to the MBO

44
Backbone Node Automatic Deployment

• Objectives
• Robust and autonomous backbone network
  maintenance
• Uniform distribution to cover the field
• Approach
• Dynamic backbone node election Deploy redundant
  backbone capable nodes and select a few
• Backbone node automatic placement Relocate
  backbone nodes from dense to sparse regions

45
Mobile Backbone Reconfiguration
46
Variable Speed with 1000 nodes
Delivery fraction while increasing mobility speed
47
LANMAR TestbedIPv6 support

• Yeng Lee

48
LANMAR implementation in IPv6 LINUX environment

• The group ID conveniently embedded in the IPv6
  address format
• A packet to remote destination is routed to
  corresponding Landmark based on IPv6 address
  lookup
• Linux testbed implementation

49
Lanmar for IPv6 environment

• Advantages
• Use IPv6s Group ID to distinguish groups
• Support many more members in each group (than
  IPv4)

Node ID (8 bits)
LANMAR subnet (24 bits)
x x x x x x x x
x x x x x x x x
x x x x x x x x
x x x x x x x x
IPv4
64 bits
16 bits
48 bits
IPv6