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A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks

IEEE Personal Communications, April 1999, pp. 46-55 E. Royer and C.-K. Toh

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Introduction

Two types of wireless networks:infrastructured network:

base stations are the bridgesa mobile host will communicate with the nearest base stationhandoff is taken when a host roams from one base to another

ad hoc network: infrastructureless: no fixed base stations

without the assistance of base stations for communication

Due to transmission range constraint, two MHs need multi-hop routing for communication

quickly and unpredictably changing topology

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MANET

MANET = Mobile Ad Hoc Networksa set of mobile hosts, each with a transceiverno base stations; no fixed network infrastructuremulti-hop communicationneeds a routing protocol which can handle changing

topology

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Applications of MANET

battlefields

nature disaster areas

fleet in oceans

historical cites

festival ground

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Related Research

IEEE 802.11 for Wireless LANsMAC PHY

IETF manet groupto stimulate research and discuss possible standards in this ar

ea

Routing Protocols:unicast – AODV, DSR, ZRP, TORA, CBRP, CEDARmulticast – MAODV, AMRoute, ODMRP, AMRIS

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Resources and Applications

NS-2:AODV, DSR, DSDV, TORA

Telcordia: Intelligent Transportation SystemAODVMAODV: to distributed emergency information

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Challenge of Ad Hoc Networks

No centralized entity

Mobile host is no longer just an end system

Acting as an intermediate system

Changing network topology over time

Every node can be mobile

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Routing in MANET

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Can Existing Internet Routing Protocols Be Used for MANET?

Link-state Routing

Distance-vector Routing

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Link State Routing: Dijkstra’s Algorithm

Each node keeps its link state to its neighbors.

From each node, we gradually expand a spanning tree, until all nodes are scanned.

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Link State Routing: Dijkstra’s Algorithm

Initial State: each host only knows its direct neighbors

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Evolution of States in C

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Evolution of States in C (cont.)

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Evolution of States in C (cont.)

Comments: This is a centralized algorithm, not appropriate.

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Overview of Current Routing Protocols

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On-demand vs. Table-driven

Table-Driven Routing Protocol:proactive!!continuously evaluate the routesattempt to maintain consistent, up-to-date routing

informationwhen a route is needed, one may be ready immediately

when the network topology changes the protocol responds by propagating updates throughout the

network to maintain a consistent view

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Source-Initiated On-Demand Routing Protocol:reactive!!on-demand style: create routes only when it is desired by the

source node route discovery: invoke a route-determination procedure the procedure is terminated when

a route has been found no route is found after all route permutations are examined

longer delay: sometimes a route may not be ready for use immediately when data packets come

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Table-Driven Routing Protocols

Protocol 1:DSDV: Destination Sequence Distance Vector

Protocol 2:CGSR: Clustered Gateway Switch Routing

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Protocol 1: DSDV (Destination Sequence Distance Vector)

“Highly Dynamic Destination-Sequence Distance-Vector Routing (DSDV) for Mobile Computers”

Charles E. Perkins & Pravin Bhagwat Dated: 1994 Computer Communications Review, ‘94 pp. 234-244

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DSDV Outline

Each node keeps a routing table to all other nodes.based on next-hop routing

Once its routing table changes, a node broadcasts its table to other nodes.

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DSDV(cont.)

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DSDV(cont.)

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Protocol 2: CGSR (Clusterhead Gateway Switch Routing)

“Routing in Clustered Multihop, Mobile Wireless Networks with Fading Channel”, C.-C. Chiang, 1996, Proc. IEEE SICON ’97, pp. 197-211.

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CGSR: Cluster Head and Gateway

The arrangement of cluster head is similar to dominating set in graph theory.Definition: each node is either in the dominating set or is

neighboring to a node in the dominating set.

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CGSR(cont.)

(5 hops)

(3 hops)

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CGSR (cont.)

A routing table among cluster heads are maintained.also based on the DSDV manner

Data forwarding steps:from cluster head to cluster head

in a hierarchical manner

then from cluster head to cluster membersbetween two cluster heads, gateways are used to forward the

packets Adv: less routing information to be kept Disadv: longer route

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Source-Initiated On-DemandRouting Protocols

AODV DSR TORA ABR SSR ZRP

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Protocol 1:AODV

AODV: Ad hoc On-demand Distance Vector routing protocolOn track to become an IETF Experimental RFC

ReferencesC. E. Perkins, E. M. Belding-Royer, and S. R. Das, “Ad hoc

On-Demand Distance Vector (AODV) Routing,” IETF Internet Draft, draft-ietf-manet-aodv-13.txt, Feb. 17, 2003 (work in progress).

C. E. Perkins and E. M. Royer, “Ad hoc On-Demand Distance Vector Routing,” Proceedings 2nd IEEE Workshop on Mobile Computing Systems and Applications, February 1999, pp. 90-100.

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AODV Concepts (1)

Pure on-demand routing protocolA node does not perform route discovery or maintenance unt

il it needs a route to another node or it offers its services as an intermediate node

Nodes that are not on active paths do not maintain routing information and do not participate in routing table exchanges

Uses a broadcast route discovery mechanism Uses hop-by-hop routing

Routes are based on dynamic table entries maintained at intermediate nodes

Comparison: Dynamic Source Routing (DSR) uses source routing

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AODV Concepts (2)

Local HELLO messages are used to determine local connectivityCan reduce response time to routing requestsCan trigger updates when necessary

Sequence numbers are assigned to routes and routing table entriesto supersede stale cached routing entries

Every node maintains two countersNode sequence numberBroadcast ID

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AODV Route Request (1)

Initiated when a node wants to communicate with another node, but does not have a route to that node

Source node broadcasts a route request (RREQ) packet to its neighbors

broadcast_id

dest_addr

type flags hopcntresvd

dest_sequence_#

source_addr

source_sequence_#

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AODV Route Request (2)

Sequence numbersSource sequence indicates “freshness” of reverse route to the

sourceDestination sequence number indicates freshness of route to

the destination Every neighbor receives the RREQ and either …

Returns a route reply (RREP) packet, orForwards the RREQ to its neighbors

(source_addr, broadcast_id) uniquely identifies the RREQbroadcast_id is incremented for every RREQ packet sentReceivers can identify and discard duplicate RREQ packets

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AODV Route Request (3)

If a node cannot respond to the RREQThe node increments the hop countThe node saves the following information to set up a reverse

path (AODV assumes symmetrical links)Neighbor that sent this RREQ packetDestination IP addressSource IP addressBroadcast IDSource node’s sequence numberExpiration time for reverse path entry (to enable garbage colle

ction)

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AODV Example (1)

Node 1 needs to send a data packet to Node 7 Assume Node 6 knows a current route to Node 7 Assume that no other route information exists in the

network (related to Node 7)

1

4

35

2

6

7

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AODV Example (2)

Node 1 sends a RREQ packet to its neighborssource_addr = 1dest_addr = 7broadcast_id = broadcast_id + 1source_sequence_# = source_sequence_# + 1dest_sequence_# = last dest_sequence_# for Node 7

1

4

35

2

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7

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AODV Example (3)

Nodes 2 and 4 verify that this is a new RREQ and that the source_sequence_# is not stale with respect to the reverse route to Node 1

Nodes 2 and 4 forward the RREQ Update source_sequence_# for Node 1Increment hop_cnt in the RREQ packet

1

4

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2

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7

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AODV Example (4)

RREQ reaches Node 6, which knows a route to 7Node 6 must verify that the destination sequence number is

less than or equal to the destination sequence number it has recorded for Node 7

Nodes 3 and 5 will forward the RREQ packet, but the receivers recognize the packets as duplicates

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2

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AODV Route Reply (1)

If a node receives an RREQ packet and it has a current route to the target destination, then it unicasts a route reply packet (RREP) to the neighbor that sent the RREQ packet

dest_addr

type flags hopcntrsvd

dest_sequence_#

source_addr

lifetime

prsz

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AODV Route Reply (2)

Intermediate nodes propagate the first RREP for the source towards the source using cached reverse route entries

Other RREP packets are discarded unless…dest_sequence_# number is higher than the previous, ordestination_sequence_# is the same, but hop_cnt is smaller (i.

e., there’s a better path) RREP eventually makes it to the source, which can use the

neighbor sending the RREP as its next hop for sending to the destination

Cached reverse routes will timeout in nodes not seeing a RREP packet

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AODV Example (5)

Node 6 knows a route to Node 7 and sends an RREP to Node 4source_addr = 1dest_addr = 7dest_sequence_# = maximum(own sequence number, dest_seque

nce_# in RREQ)hop_cnt = 1

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2

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AODV Example (6)

Node 4 verifies that this is a new route reply (the case here) or one that has a lower hop count and, if so, propagates the RREP packet to Node 1Increments hop_cnt in the RREP packet

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4

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2

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AODV Example (7)

Node 1 now has a route to Node 7 in three hops and can use it immediately to send data packets

Note that the first data packet that prompted path discovery has been delayed until the first RREP was returned

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2

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Dest Next Hops

7 4 3

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AODV Route Maintenance

Route changes can be detected by…Failure of periodic HELLO packetsFailure or disconnect indication from the link levelFailure of transmission of a packet to the next hop (can detec

t by listening for the retransmission if it is not the final destination)

The upstream (toward the source) node detecting a failure propagates an route error (RERR) packet to the source node with a new destination sequence number and a hop count of infinity (unreachable)

The source (or another node on the path) can rebuild a path by sending a RREQ packet

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AODV Example (8)

Assume that Node 7 moves and link 6-7 breaks Node 6 issues an RERR packet indicating the broken path The RERR propagates back to Node 1 Node 1 can discover a new route

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2

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Protocol 2: DSR (Dynamic Source Routing)

“Dynamic Source Routing in Ad-Hoc Wireless Networks”, D. B. Johnson and D. A. Maltz, Mobile Computing, 1996, pp. 153-181.

on-demand Each host maintains a route cache which contains all route

s it has learnt. Source Routing:

routes are denoted with complete information (each hop is registered)

Two major parts:route discoveryroute maintenance

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Route Discovery Route Reply

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Route Discovery of DSR

When a host has a packet to send, it first consults its route cache.If there is an unexpired route, then it will use it.Otherwise, a route discovery will be performed.

Route Discovery:There is a “route record” field in the packet.

The source node will add its address to the record.On receipt of the packet, a host will add its address to the “route

record” and rebroadcast the packet.

To limit the number of ROUTE_REQUEST packets:Each node only rebroadcasts the packet at most once.Each node will consult its route cache to see if a route is already

known.

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ROUTE_REPLY of DSR

A ROUTE_REPLY packet is generated whenthe route request packet reaches the destinationan intermediate host has an unexpired route to the

destination The ROUTE_REPLY packet will contain a route

generated in two manner:from destination:

the route that was traversed by the ROUTE_REQUEST packet

from intermediate host: the route that was traversed by the ROUTE_REQUEST packet

concatenated with the route in the intermediate host’s route cache

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Stale Route Cache Problem

Definition:A route may become broken (i.e., stale), but is unaware by a

host X. With route cache, host X may keep on distributing erroneous

information to other hosts.

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Route Maintenance of DSR

When the data link layer encounters a link breakage, a ROUTE_ERROR packet will be initiated.The packet will traverse in the backward direction to the

source.The source will then initiate another ROUTE_REQUEST.Example: (next page)

Maintenance of route cache:All routes which contain the breakage hop have to be

removed from the route cache.

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x

Route_Error

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Packet Type: Route Request (RREQ)

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Packet Type: Route Reply (RREP)

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Packet Type: Data Packet

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Packet Type: Route_Error

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Route Concentration Problem

With route cache, hosts are likely to share the same links (routes).

(1)

(2)

(3) (4)

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Protocol 3: TORA(Temporally Ordered Routing Algorithm)

“A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks”, University of Maryland, V. D. Park and M. S. Corson, 1996, Proc. INFOCOM ’97.

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TORA Outline

source-initiated protocol provide multiple paths for

any source-destination pairLike water flowing, it

goes from upstream to downstream.

for highly dynamic mobile networks

high level

low level

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Main Idea

Regard the network as a directed graph. For each destination, a DAG (directed acyclic graph) will

be maintained.Note: There are n copies of DAG’s, each associated with one

destination, where n is the number of hosts.In the following discussion, we only discuss one DAG associ

ated with a destination. The DAG is accomplished by assigning each node i a heig

ht metric hi.

A link from i to j means hi > hj.

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Full Reversal Method

A node will update its height to adapt to the change of network topology.

Height hi = (valuei, IDi)a node will change its value to change the direction of a link

Relation: hi > hj if the following is true:

valuei > valuej

(valuei = valuej) and (Di > Dj)

Ex: (5, 4) > (4, 6)Ex: (5, 4) > (5, 2)Property: Given any to heights, there must exist a “>” relatio

n between them.

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Rule:Each node other than the destination that has no outgoing

links reverses the direction of ALL its incoming links.This means that the node’s height is a local minimum.

This is done by getting a larger height such that the node becomes a local maximum.MAX{all neighbors’ heights} + 1

Example: a graph with a random direction for each link

a, 5b, 6

e, 3

d, 4c, 3

dest, 8 g, 2

f, 1

a, 5b, 6

e, 3

d, 4c, 3

dest, 8 g, 2

f, 1

a, 5b, 6

e, 3

d, 4c, 9

dest, 8 g, 2

f, 4

original network

a, 5b, 6

e, 6

d, 4c, 9

dest, 8 g, 5

f, 4

a, 7b, 6

e, 6

d, 9c, 9

dest, 8 g, 5

f, 7

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a, 7b, 10

e, 10

d, 9c, 9

dest, 8 g, 10

f, 7

a, 11b, 10

e, 10

d, 9c, 9

dest, 8 g, 10

f, 11

Eventually, the DAG will stablize.

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TORA Details

Three basic functions:route creation route maintenanceroute erasure

Three control packets:query (QRY)update (UPD)clear (CLR)

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Data Structure

Each node keep a 5-tuple (τ, oid, r, δ, i)τ: time of the link failure.oid (originator ID):

Unique identifier of the node that defined a new reference level

Most likely, the node who detects link breakage.

r: reflection indicator bit. initially set to 0.

δ: propagation ordering parameter (i.e., height)i: node ID

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Creating Routes

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Maintaining Routes

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Maintaining Routes (with Reaction)

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Maintaining Routes (cont.)

The reflection bit (r)is used here to mean“no exit”.

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Protocol 4: ABR(Associativity-Based Routing)

ABR considers the stability of a link.The metric is called degree of association stability.

Basic Idea:Each node periodically generates a beacon to signify its

existence.On receipt of the beacon, a neighboring node will increase

the “tick” of the sender by 1.A higher degree of association stability (i.e., ticks) may

indicate a low mobility of that node.A low degree of association stability may indicate a high

mobility of that node.When a link becomes broken, the node will set the tick of

the other node to 0.

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ABR Outline

Route Discovery:(similar to DSR)

On needing a route, a host will broadcast a ROUTE_REQUEST packet.

Each receiving host will append its address to the packet.

The association stability (represented by “ticks”) is also appended in the ROUTE_REQUEST packet.

The destination node will select the best route (in terms of association stability), and then respond a packet to the source.

source destination

5

8

7

10

4

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Route Reconstruction:On route error, a node will perform a local search in hope of

rebuild the path.If the local search fails, a ROUTE_ERROR will be reported

to the source.

localsearched zone

source

destination

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Protocol 5: SSA(Signal Stability-Based Adaptive Routing)

“Signal Stability-Based Adaptive Routing (SSA) for Ad Hoc Wireless Networks”

University of Maryland R. Dube, C. D. Rais, K.-Y. Wang & S. K. Tripathi IEEE Personal Communications, ‘97 pp. 36-45

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Basic Idea of SSA

Observation:The ABR only considers the connectivity to nodes.

Two more metrics:signal stability:

the strength of a signalprovided by link layer

location stabilityhow fast a host movescould be measure by:

the change of signal strength over a period of time location devices (such as GPS)

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SSA

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SSA(cont.)

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Protocol 6: ZRP(Zone Routing Protocol)

The Zone Routing Protocol (ZRP) for Ad Hoc Networks Cornell University Z.J. Haas and M.R. Pearlman draft-ietf-manet-zone-zrp-01.txt, 1998

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ZRP Outline

Hybrid of table-driven and on-demand!!

From each node, there is a concept of “zone”.Within each zone, the routing is performed in a table-driven

manner (proactive).However, a node does not try to keep global routing

information.

For inter-zone routing, on-demand routing is used.This is similar to DSR.

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ZRP Example

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Route Discovery

By an operation called “boardercast”:sending the route-request to boarder nodes

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Comparison of Table-Driven and On-Demand Protocols

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Research Highlight: Resource Allocation by Pricing

Ref: Y. Xue, et al., “Optimal resource allocation in wireless ad hoc networks: a price-based approach”, IEEE Trans. on Mobile Computing, 2006.

Goal: A mobile might be selfish by asking others to relay its data, but avoiding relaying data of others.

Approaches:using clique to represent interference relations:

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cont.

price of a clique: going up when the demand is higher than requestedgoing down when the demand is lower than requested

sources of flows:adding more traffic when path price is going down reducing traffic when path price is going up