Reliability Management in Mobile Ad Hoc Networkskato/workshop2005/NEC-slide.pdf · 2005. 1. 31. ·...

Reliability Managementin Mobile Ad Hoc Networks

Tomohiko Yagyu, Masahiro Jibiki, Yoshiaki Kiriha

NEC

January 27 2005The 2005 Sendai International Workshop on

Network Security and Wireless Communication

2© NEC Corporation 2005

Mobile Ad Hoc Network (Manet)

• a network that is comprised of mobile nodes with wireless interface(s).– multi hop forwarding through

wireless network• each node automatically joins

the network– users can communicate each

other without infrastructures such as access points and cellular networks

– users can move freely


Manet Applications

• Inter-vehicle communication for ITS– accident information on a highway– collision avoidance at a crossroad– connection to the Internet

• Mobile Office– ad hoc meeting outside the office

• Disaster Relief– communication among rescue teams

• battle field– communication within a troop


Reliability Requirement in Manet

• High reliability– inter-vehicle safety information (collision alert

etc).• Fair reliability

– communication in the disaster-stricken area.• Best Effort

– Web access in a car– ad hoc meeting in an office


Characteristics of Manet

• neighbor density– Throughput decreases due to collisions.

• node mobility– Routes (next hop to the destination) frequently change

due to the movement.• link connectivity

– Link connectivity is frequently lost due to the obstacles or phasing.

– link flapping (a link repeatedly goes short-term down)


Communication techniques in Manet

• Broadcast– all nodes in manet receive broadcast packets– adaptive for high mobility because no routing (route

calculation or route establishment) is necessary.• Dynamic Routing

– each node forwards packets toward the destination.– forwarding decisions are based on distance, topology,

position etc...– route re-calculation or route repair is initiated after

detecting link failures.


Broadcasting techniques for wireless networks

• probabilistic protocols– a random number or threshold is used to make a

decision whether a node rebroadcast the packet or not.

– it can not ensure that all nodes receive the packet

• deterministic protocols– any decisions never rely on random numbers.– it ensures all nodes receive the packet, if the

MAC layer is ideal.


Probabilistic Broadcast Protocols

• probability based scheme– rebroadcast received packets with

probability p.• counter based scheme

– rebroadcast if and only if the node received the message from less than C neighbors.

• distance based scheme– rebroadcast if and only if the distance

between the nodes is greater that threshold D.

• area based scheme– rebroadcast if and only if the difference

of the coverage areas is greater than threshold A.


Deterministic Broadcast protocols

• Dominating Set (a set of nodes which rebroadcast packets) is calculated from neighborhood information.

• The problem to minimize the size of dominating set is NP-complete.– so, many heuristic algorisms are proposed.

• e.g. Multi Point Relay (MPR)– Every node has 2-hop neighbor knowledge via periodic

“hello” packet– Each node selects Multi Point Relays (MPR) to cover

all 2-hop neighbors.– The node that is selected as MPR rebroadcast packets

received from the MPR selector.– It depends on a node which sends a packet whether a

node rebroadcast the received packet or not.


Multi Point Relay

RouterA

Router11

Router13

Router22

Router24

Router26

Router21

Router23

Router25

Router14

MPRRouter

12

1 Hop symmetric neighbors

2 Hop away symmetric neighbors

MPRSelector

MPR


Dynamic routing for Wireless network

• Reactive approach– Route Request is initiated when the route is necessary.

• e.g. AODV (Ad Hoc On-Demand Distance Vector Routing), DSR (Dynamic Source Routing)

• Proactive approach– Each node maintains a route to every other node at all time.

• e.g. OLSR (Optimized Link State Routing), TBRPF (Topology Dissemination Based on Reverse Path Forwarding)

• Hybrid approach– proactive method is used within k-hop area, farther reactive method..

• e.g. ZRP (Zone Routing Protocol)• Location aided approach

– Reactive approach which restricts route request flooding by destination location

• e.g. LAR (Location Aided Routing)• Position based approach

– each node decides the next hop node based on the destination location information including the packet.

• e.g. GPSR (Greedy Perimeter Stateless Routing)


Reactive approach

• On-demand routing• When a source node needs to

send packets to a destination, it performs a route discovery (only if it has no route to the destination).

• The route request packet is typically broadcasted network-wide.

• The route reply packet is sent back along reverse path of RREQ. SRC

DEST

RREQ

RREQ

RREQ

RREQ

RREQ

RREQ

RREQ

RREQ

RREP

RREP

RREQ

RREQ：Route RequestRREP：Route Reply

established route


Proactive approach

• They derive from the traditional internet routing protocols such as distance vector (RIP etc) and link state (OSPF etc).

• Periodic update of routing information.

• Every node in the network maintains the routes to all other nodes.

• Overhead to maintain up-to-date route is high.

MPRA

Hello

MPR

MPR

Shortest Path Tree for A


Hybrid Approach

S

A

B

Periphery Nodes

S’s Zone RadiusA’s Zone Radius

route discoveryoutside the zone


Location Aided approach

• Reactive approach which restrict route request by the estimation of destination’s location.

• A source node calculates the Expected Zone and Request Zone.

• Expected Zone is the area in which the destination node is most likely to be discovered.

• Request Zone is the area in which the route request should be propagated.

• Source node must know– previous location of the

destination at time t0– velocity of the destination node

S

D

Expected Zone

Request Zone


Position based approach

• Each node has the knowledge of its neighbors’position via periodic beacon.

• A source node can get the position of the destination. (location service is mandatory).

• A node select the nearest neighbor to the destination as a next hop for packet forwarding.

Dest

Src


Mapping of techniques (1)

mobility

reliability

low high

low

high

Broadcast

ProactiveRouting

ReactiveRouting

Position-basedRouting

?


Reliable Communication techniques for wired networks

• Broadcast is too costly for a low mobility or dense network or unicast communication.

• In a low mobility situation, we can apply reliable communication techniques for wired networks to wireless networks.– link state routing protocols allow us handle wireless

network as virtually point-to-point network.• Fast reroute

– Failed link is locally bypassed.• Path Protection

– Plural paths are established for a connection..


Fast Reroute

• Fast reroute technique is developed based on MPLS

• A bypass (detour) path is set up before failures.

• Local repair enables to recover from the failure fast

• Many bypass paths consume a lot of resources.

S DR1 R2 R3

R4 R5 R6

Protected LSPLabel:L1

Label:L5

Label:L6 Label:L7

Label:L8

Label:L4

one to one backup

facility backup

S1 D1R1 R2 R3

R4 R5 R6

S2 D2Label:L21 Label:L24

Label:L11 Label:L14

L31/L14 L31/L24 L34/L14L34/L24

L32/L14L32/L24

L33/L14L33/L24


Path Protection

• Path Protection scheme is discussed in IETF MPLS/CCAMP-WG.

• Dedicated 1+1– Two paths are established for one

connection.– Data packets run on both paths

• Dedicated 1:1– Work and backup paths are

established for a connection.– Data packets traverse on only the

work path.– When the work path failed, source

node switch packets to the backup path.

Src Dst

Src Dst

Dedicated 1+1

Dedicated 1:1


Mapping of techniques (2)

mobility

reliability

low high

low

highPath

Protection

Fast Reroute

ProactiveRouting

ReactiveRouting

Position-basedRouting

Broadcast


Path Protection for Wireless NW

• What are the problems to apply the Path protection technique to the wireless network?– unstable link status

• short-term link failures often occur due to interference, obstacle etc...

• such failures degrade packet reachability and cause much routinginformation update.

– simultaneous link failures• two paths (work and backup) is not enough.• it is necessary to keep path redundancy. No body may repair

broken link in wireless network.

– poor resource/bandwidth• control traffic (signaling, routing, etc) is a very heavy load for the

network.


Path Protection for Wireless NW (Cont.)

• To reduce the effect of unstable link status– we introduce “flickering” status in link state

management. to prevent link status flapping.

Administratively down

Flickering

Up

Down

Administrativelyup

Continuation oflink interruption

Continuation ofFlickering status

link interruption

Continuation oflink restoration

link restoration

link restoration


Path Protection for Wireless NW (Cont.)

• simultaneous link failures• poor resource/bandwidth

– when a node starts communication, plural disjoint paths (Nmax) are established.

– To reduce path recovery overhead, a source node refrains from recovering paths broken by link failure until available paths are less than Nmin .

– To keep path redundancy, a source node initiates path recovery when available paths are less than Nmin.

NotifyLink failure

Link failure

Initiator

Terminator

Link failure

Link failure

Initiator

TerminatorAlternative PathsCalculation

AlternativePath#1

Alternative Path#2


Fast Reroute for Wireless NW

• motivation– reduce network-wide flooding of routing update due to short-term

link failures.– decrease packet loss when a link failure occurs.

• What are the problems to apply fast reroute technique to the wireless networks?– short-term link failures– frequent topology change

• pre-setup of detour path is no good.


Multilayer Fast Rerouting

• Introduce “flickering” status in link status management.

• A detour path is established after a link failure occurs.

• The detour is only to the next hop.

• Sub layer under IP (e.g. MPLS) forwards detoured packets.

• The detour path is kept until dynamic routing process complete (new routes become available).

D

E

CBA establish

detour Path

packet traversing detour path

D

E

CBA delete

detour path

D

E

CBA


Scalability Issue

• link state routing protocol– e.g. OLSR

• periodic hello• Network-wide flooding using MPR of Link state update

– overhead is severe for wireless network with poor bandwidth• Hello at log interval delay detecting the disappearance of neighbor

nodes.– Node movement breaks MPR relation.

• flooding mechanism is intolerant of high mobility.• Our approach

– adjusting hello and routing update interval– detecting neighborhood change from routing information– switching flooding mechanism of routing update as the case may

be.


Manet Routing Protocol with Hello Interval Adjustment

Node41（on the move）

Node42

Node43

Node44

Node45

Hello 100

Hello 102

Hello 103Hello 104

Topology InfoOriginator Node42Link#1 Node41 Hello=104・・・

Hello at short interval

Detecting movement of Node41 from Topology Info.

Flooding Topology Info.independent of MPR

MPR relation

Neighbor Table on Node45

Node41 Latest Hello=100・・・




Conclusion

• To achieve required reliability, we should apply an appropriate technique with taking characteristics of manet into consideration.– we categorize the appropriate techniques with regard to

the characteristics of Manet.• It can be possible to apply traditional reliable

communication techniques for wired networks to manet with some adaptations.– we present the adaptation of Path Protection/Fast

Reroute techniques for MPLS to Manet.• Scalability of the routing protocol is one of major

issues in wireless network.– we present a possible improvement for a link state

routing protocol.


Future Work

• In the very dense Manet– improve scalability of a routing protocol– minimize routing convergence time

• QoS in Manet– Manet-wide resource assignment

Reliability Management in Mobile Ad Hoc Networkskato/workshop2005/NEC-slide.pdf · 2005. 1. 31. ·...

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