Reliability Management in Mobile Ad Hoc Networkskato/workshop2005/NEC-slide.pdf · 2005. 1. 31. ·...
Transcript of 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
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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
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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
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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
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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)
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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.
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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.
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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.
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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.
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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
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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)
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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
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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
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Hybrid Approach
S
A
B
Periphery Nodes
S’s Zone RadiusA’s Zone Radius
route discoveryoutside the zone
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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
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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
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Mapping of techniques (1)
mobility
reliability
low high
low
high
Broadcast
ProactiveRouting
ReactiveRouting
Position-basedRouting
?
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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..
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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
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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
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Mapping of techniques (2)
mobility
reliability
low high
low
highPath
Protection
Fast Reroute
ProactiveRouting
ReactiveRouting
Position-basedRouting
Broadcast
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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.
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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
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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
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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.
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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
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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.
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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・・・
Topology InfoOriginator Node42Link#1 Node41 Hello=104・・・
Topology InfoOriginator Node42Link#1 Node41 Hello=104・・・
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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.
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Future Work
• In the very dense Manet– improve scalability of a routing protocol– minimize routing convergence time
• QoS in Manet– Manet-wide resource assignment