Ad Hoc Networks

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Ad Hoc Networks

• Cholatip Yawut
• Faculty of Information Technology
• King Mongkut's University of Technology North
  Bangkok

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IEFT MANET Working Group

• Goals
• standardize an interdomain unicast (IP) routing
  protocol
• define modes of efficient operation
• support both static and dynamic topologies
• A dozen candidate routing protocols have been
  proposed

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Routing
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Ants Searching for Food
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from Prof. Yu-Chee Tsengs slides
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Routing (Ants scenario)
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Three Main Issues in Ants Life

• Route Discovery
• searching for the places with food
• Packet Forwarding
• delivering foods back home
• Route Maintenance
• when foods move to new place

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Introduction
Ref Optimized Link State Routing Protocol for Ad
Hoc Networks Jacquet, p and park gi won
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Reactive versus Proactive routing approach

• Proactive Routing Protocols
• Periodic exchange of control messages
• immediately provide the required routes when
  needed
• - Larger signalling traffic and power
  consumption.
• Reactive Routing Protocols
• Attempts to discover routes only on-demand by
  flooding
• Smaller signalling traffic and power
  consumption.
• - A long delay for application when no route to
  the destination available

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Routing Protocols

• Proactive (Global/Table Driven)
• route determination at startup
• maintain using periodic update
• Reactive (On-demand)
• route determination as needed
• route discovery process
• Hybrid
• combination of proactive and reactive

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Proactive

• Destination-sequenced distance vector (DSDV)
• Wireless routing protocol (WRP)
• Global state routing (GSR)
• Fisheye state routing (FSR)
• Source-tree adaptive routing (STAR)
• Distance routing algorithm for mobility (DREAM)
• Cluster-head gateway switch routing (CGSR)
• OLSR (Optimized Link State Routing)

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Reactive

• Associativity-base routing (ABR)
• Dynamic source routing (DSR)
• Ad hoc on-demand distance vector (AODV)
• Temporally ordered routing algorithm (TORA)
• Routing on-demand acyclic multi-path (ROAM)
• Light-weight mobile routing (LMR)
• Signal stability adaptive (SSA)
• Cluster-based routing protocol (CBRP)

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Hybrid

• Zone routing protocol (ZRP)
• Zone-based hierarchical link state (ZHLS)
• Distributed spanning trees (DST)
• Distributed dynamic routing (DDR)
• Scalable location update routing pro. (SLURP)

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Flooding

• Simplest of all routing protocols
• Send all info to everybody
• If data not for you, send to all neighbors
• Robust
• destination is guaranteed to receive data
• Resource Intensive
• unnecessary traffic
• load increases, network performance drops quickly

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Routing Examples

• Destination Sequenced Distance Vector (DSDV)
• Cluster Gateway Switch Routing (CGSR)
• Ad hoc On-demand Distance Vector (AODV)
• Dynamic Source Routing (DSR)
• Zone Routing Protocol (ZRP)
• Location-Aided Routing (LAR)
• Distance Routing effect Algorithm for mobility
  (DREAM)
• Power-Aware Routing (PAR)

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Destination Sequenced Distance Vector (DSDV)

• Table-driven
• Based on the distributed Bellman-Ford routing
  algorithm
• Each node maintains a routing table
• Routing hops to each destination
• Sequence number

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DSDV

• Problem
• a lot of control traffic in the network
• Solution two types of route update packets
• full dump (All available routing info)
• incremental (Only changed info)

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Cluster Gateway Switch Routing (CGSR)

• Table-driven for inter-cluster routing
• Uses DSDV for intra-cluster routing

M2
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Ad hoc On-demand Distance Vector (AODV)

• On-demand driven
• Nodes that are not on the selected path do not
  maintain routing information
• Route discovery
• source broadcasts a route request packet (RREQ)
• destination (or intermediate node with fresh
  enough route to destination) replies a route
  reply packet (RREP)

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AODV
RREQ
RREP
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AODV

• Problem
• a node along the route moves
• Solution
• upstream neighbor notices the move
• propagates a link failure notification message to
  each of its active upstream neighbors
• source receives the message and re-initiate route
  discovery

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Dynamic Source Routing (DSR)

• On-demand driven
• Based on the concept of source routing
• Required to maintain route caches
• Two major phases
• Route discovery (flooding)
• Route maintenance
• A route error packet

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DSR
Route Discovery
Route Reply
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Modified DSR

• Route information determined by the current
  network conditions
• number of hops
• congestion
• node energy
• Other considerations
• fairness
• number of route requests

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Zone Routing Protocol (ZRP)

• Hybrid protocol
• On-demand
• Proactive
• ZRP has three sub-protocols
• Intrazone Routing Protocol (IARP)
• Interzone Routing Protocol (IERP)
• Bordercast Resolution Protocol (BRP)

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Zone Routing Protocol (ZRP)
Zone of Node Y
Border Node
Zone Radius r Hops
Border Node
Node X
Zone of Node Z
Node Z
Zone of Node X
Bordercasting
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Location-Aided Routing (LAR)

• Location information via GPS
• Shortcoming (maybe not anymore 2005)
• GPS availability is not yet worldwide
• Position information come with deviation

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Location-Aided Routing (LAR)

• Each node knows its location in every moment
• Using location information for route discovery
• Routing is done using the last known location
  an assumption
• Route discovery is initiated when
• S doesnt know a route to D
• Previous route from S to D is broken

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LAR - Definitions

• Expected Zone
• S knows the location L of D in t0
• Current time t1
• The location of D in t1 is the expected zone
• Request Zone
• Flood with a modification
• Node S defines a request zone for the route
  request

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LAR
Destination (Xd,Yd)
R
source(Xs,Ys)
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Distance Routing effect Algorithm for mobility
(DREAM)

• Position-based
• Each node
• maintains a position database
• regularly floods packets to update the position
• Temporal resolution
• Spatial resolution

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Restricted Directional Flooding

• Distance Routing effect Algorithm for mobility
  (DREAM)
• Sender will forward the packet to all one-hop
  neighbors that lie in the direction of
  destination
• Expected region is a circle around the position
  of destination as it is known to source
• The radius r of the expected region is set to
  (t1-t0)Vmax, where t1 is the current time, t0 is
  the timestamp of the position information source
  has about destination, and Vmax is the maximum
  speed that a node may travel in the ad hoc
  network
• The direction toward destination is defined by
  the line between source and destination and the
  angle ?

From ECE 5970 Class
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DREAM
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Power-Aware Routing (PAR)
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OLSR - Overview

• OLSR
• Inherits Stability of Link-state protocol
• Selective Flooding
• only MPR retransmit control messages
• Minimize flooding
• Suitable for large and dense networks

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OLSR Multipoint relays (MPRs)

• MPRs Set of selected neighbor nodes
• Minimize the flooding of broadcast packets
• Each node selects its MPRs among its on hop
  neighbors
• The set covers all the nodes that are two hops
  away
• MPR Selector a node which has selected node as
  MPR
• The information required to calculate the
  multipoint relays
• The set of one-hop neighbors and the two-hop
  neighbors
• Set of MPRs is able to transmit to all two-hop
  neighbors
• Link between node and its MPR is bidirectional.

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OLSR Multipoint relays (cont.)

• To obtain the information about one-hop neighbors
  
• Use HELLO message (received by all one-hop
  neighbors)
• To obtain the information about two-hop neighbors
  
• Each node attaches the list of its own neighbors
• Once a node has its one and two-hop neighbor sets
  
• Can select a MPRs which covers all its two-hop
  neighbors

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OLSR Multipoint relays (cont.)
4 retransmission to diffuse a message up to 2 hops
Figure 1. Diffusion of a broadcast message using
multipoint relays
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OLSR Multipoint relays (cont.)
E
D
F
A
C
G
B
Figure 2. Network example for MPR selection
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OLSR Multipoint relays (cont.)
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Protocol functioning Neighbor sensing

• Each node periodically broadcasts its HELLO
  messages
• Containing the information about its neighbors
  and their link status
• Hello messages are received by all one-hop
  neighbors
• HELLO message contains
• List of addresses of the neighbors to which there
  exists a valid bi-directional link
• List of addresses of the neighbors which are
  heard by node( a HELLO has been received )
• But link is not yet validated as bi-directional

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Protocol functioning Neighbor sensing (cont.)
Message type Vtime Message size Message size
Originator Address Originator Address Originator Address Originator Address
Time To Live Hop count Message Sequence Number Message Sequence Number
Reserved Reserved Htime Willingness
Link code Reserved Link message size Link message size
Neighbor Interface Address Neighbor Interface Address Neighbor Interface Address Neighbor Interface Address
Neighbor interface Address Neighbor interface Address Neighbor interface Address Neighbor interface Address

Reserved Reserved Htime Willingness
Link code Reserved Link message size Link message size
Neighbor interface address Neighbor interface address Neighbor interface address Neighbor interface address
Neighbor interface address Neighbor interface address Neighbor interface address Neighbor interface address

Link type Neighbor type
Table 1. Hello Message Format in OLSR
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Protocol functioning Neighbor sensing (cont.)

• HELLO messages
• Serves Link sensing
• Permit each node to learn the knowledge of its
  neighbors up to two-hops (neighbor detection)
• On the basis of this information, each node
  performs the selection of its multipoint relays
  (MPR selection signaling)
• Indicate selected multipoint relays
• On the reception of HELLO message
• Each node constructs its MPR Selector table

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Protocol functioning Neighbor sensing ( cont.)

• In the neighbor table
• Each node records the information about its on
  hop neighbor and a list of two hop neighbors
• Entry in the neighbor table has an holding time
• Upon expiry of holding time, removed
• Contains a sequence number value which specifies
  the most recent MPR set
• Every time updates its MPR set, this sequence
  number is incremented

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Protocol functioning Neighbor sensing

• Example of neighbor table

One-hop neighbors
Two-hop neighbors
State of Link
Neighbors id
Access though
Neighbors id
Bidirectional
B
C
E
Unidirectional
G
C
D
MPR
C




Table 2. Example of neighbor table
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Protocol functioning Multipoint relay selection

• Each node selects own set of multipoint relays
• Multipoint relays are declared in the transmitted
  HELLO messages
• Multipoint relay set is re-calculated when
• A change in the neighborhood( neighbor is failed
  or add new neighbor )
• A change in the two-hop neighbor set
• Each node also construct its MPR Selector table
  with information obtained from the HELLO message
• A node updates its MPR Selector set with
  information in the received HELLO messages

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Protocol functioning MPR information declaration

• TC Topology control message
• In order to build intra-forwarding database
• Only MPR nodes forward periodically to declare
  its MPR Selector set
• Message might not be sent if there are no updates
• Contains
• MPR Selector
• Sequence number
• Each node maintains a Topology Table based on TC
  messages
• Routing Tables are calculated based on Topology
  tables

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Protocol functioning MPR information
declaration (cont.)
Destination address Destinations MPR MPR Selector sequence number Holding time
Last-hop node to the destination. Originator of
TC message
MPR Selector in the received TC message
Table 3. Topology table
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Protocol functioning MPR information
declaration (cont.)
Figure 4. TC message and Topology table
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Protocol functioning MPR information
declaration (cont.)

• Upon receipt of TC message
• If there exist some entry to the same
  destination with higher Sequence Number, the TC
  message is ignored
• If there exist some entry to the same destination
  with lower Sequence Number, the topology entry
  is removed and the new one is recorded
• If the entry is the same as in TC message, the
  holding time of this entry is refreshed
• If there are no corresponding entry the new
  entry is recorded

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Protocol functioning MPR information
declaration (cont.)
Dest address Dest MPR MPR Selector sequence
X M 1
Y M 1
Z M 1
.. .. ..
S Topology table
TC originator MPR selector MPR selector sequence
M X 2
M Y 2
M Z 2
M R 2
Figure 5. Topology table update
TC message ( M send to S)
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Protocol functioning Routing table calculation

• Each node maintains a routing table to all known
  destinations in the network
• After each node TC message receives, store
  connected pairs of form ( last-hop, node)
• Routing table is based on the information
  contained in the neighbor table and the topology
  table
• Routing table
• Destination address
• Next Hop address
• Distance
• Routing Table is recalculated after every change
  in neighbor table or in topology table

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Protocol functioning Routing table calculation
(cont.)
(last-hop, destination)
Source
(last-hop, destination)
(last-hop, destination)
Destination
(last-hop, destination)
Figure 5. Building a route from topology table
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conclusion

• OLSR protocol is proactive or table driven in
  nature
• Advantages
• Route immediately available
• Minimize flooding by using MPR
• OLSR protocol is suitable for large and dense
  networks

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Current routing protocols

• Many do not consider energy conservation
• lead to partitions
• shorten network life
• fairness to intermediate nodes not incorporated
• fail to work well in both sparse and dense
  networks

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Interesting Research Topics

• Energy Awareness Routing
• Multipath Routing
• more paths used to send information, more
  reliable the transmission
• Clustering (Hierarchical Routing)
• dynamic management of subnetworks

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More Research Topics

• Topology Control
• adjustment of transmission power to simplify
  routing
• Internetworking
• managing wired and wireless networks
• Heterogeneous Networks
• Different devices on the network have different
  capabilities
• Content Aware Networks
• Location of services within the network (Printers)

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References

• Ad Hoc Mobile Wireless Networks Protocols and
  System, C-K Toh, Prentice Hall, 2002, ISBN
  0-13-007817-4
• Introduction to Ad Hoc Networking, Prof.
  Yu-Chee Tseng
• Optimized Link State Routing Protocolfor Ad Hoc
  Networks, Jacquet, p and park gi won
• Ad Hoc Network, Wireless LANs, June September
  2009, Asso. Prof. Anan Phonphoem, Ph.D.