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Ad Hoc Networks

Cholatip YawutFaculty of Information TechnologyKing 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

from Prof. Yu-Chee Tseng’s 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

Routing Protocol for MANET

Table-Driven/Proactive

Hybrid

Distance

Vector

Link-State

ZRP DSRAODVTORA

LANMARCEDAR

DSDV OLSRTBRPFFSRSTAR

MANET: Mobile Ad hoc Network

(IETF working group)

On-Demand-driven/Reactive

Clusterbased/

Hierarchical

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

C3

C2

C1

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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

N2

N4N1

N3

N5

N6

N7

N8

Source

Destination

N2

N4N1

N3

N5

N6

N7

N8

Source

Destination

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

N2

N4N1

N3

N5

N6

N7

N8

N1

N1

N1-N2

N1-N3-N4

N1-N3-N4

N1-N3-N4-N7

N1-N3-N4-N6N1-N3

N1-N3-N4

N1-N2-N5

N2

N4N1

N3

N5

N6

N7

N8N1-N2-N5-

N8

N1-N2-N5-N8

N1-N2-N5-N8

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 Radius = r Hops

Zone of Node Y

Node X

Zone of Node XNode ZZone of Node Z

Border Node

Border Node

Bordercasting

Zone Routing Protocol (ZRP)

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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

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 doesn’t 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

source(Xs,Ys)

Request ZoneExpected Zone (Xd+R, Yd+R)

R

Destination (Xd,Yd)

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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

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 30

From ECE 5970 Class

DREAM

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Power-Aware Routing (PAR)

+

–

+

–

+

–

+

–

+

–

+

–

SRC

N1 N2

DEST

N4N3

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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 it’s 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.)

Figure 1. Diffusion of a broadcast message using multipoint relays

4 retransmission to diffuse a message up to 2 hops

MPR(Retransmission node)

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OLSR – Multipoint relays (cont.)

Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)

B A,C,F,G D,E C

A

B

C

D

E

F

G

Figure 2. Network example for MPR selection

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OLSR – Multipoint relays (cont.)

MS(A) = {B,H,I}

A

G

F HE

ID C B

MS(C) = {B,D,E} MPR(B) = {A,C}

Figure 3. MPR 과 MPR Selector Set

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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

Originator Address

Time To Live Hop count Message Sequence Number

Reserved

HtimeWillingness

Link code Reserved Link message size

Neighbor Interface Address

Neighbor interface Address

…

Reserved Htime Willingness

Link code Reserved Link message size

Neighbor interface address

Neighbor interface address

…

Table 1. Hello Message Format in OLSR

Link type Neighbor type

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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

……

MPRC

UnidirectionalG

BidirectionalB

State of LinkNeighbor’s id

Two-hop neighbors

……

CD

CE

Access thoughNeighbor’s id

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 Destination’s MPR MPR Selector sequence number

Holding time

MPR Selector in the received TC message

Last-hop node to the destination.

Originator of TC message

Table 3. Topology table

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Protocol functioning – MPR information declaration (cont.)

G

FE

D C B

MS(C) = {B,D,E} MPR(B) = {A,C}

Figure 4. TC message and Topology table

Send TC message

{B,D,E} build the 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.)

S

B

D

M

X YZ

P

A

Send TC message

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

TC message ( M send to S)

R

Figure 5. Topology table update

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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.)

Source

Destination

(last-hop, destination)

(last-hop, destination)

(last-hop, 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.