redes inalámbricas – tema 3. mobile ad hoc networks

REDES INALÁMBRICAS Máster de Ingeniería de Computadores-DISCA

Redes Inalámbricas – Tema 3. Mobile Ad Hoc Networks

A. Specific propertiesB. Flooding as a basic mechanismC. Basic routing protocols

DSR AODV y DYMO OLSR y OLSRv2

D. Advanced protocols and techniques

Acknowledgments :Nitin H. Vaidya, “Tutorial on Mobile Ad Hoc

Networks: Routing, MAC and Transport Issues” Available at:

http://www.crhc.uiuc.edu/wireless/tutorials.html

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10 Wireless ad hoc network3

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10 Unit disk graph

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Routing Overview Goal: transfer message from one

node to another Which is the “best” path? Generally try

to optimize one of the following: Shortest path (fewest hops) Shortest time (lowest latency) Shortest weighted path (utilize

available bandwidth, battery) Who decides - source or intermediate

nodes? Source (“path”) routing [Like airline

travel] Source specifies entire route Intermediate nodes just forward

to specified next hop Destination (“hop-by-hop”) routing

[Like postal service] Source specifies only destination

in message header Intermediate nodes look at

destination in header, consult internal tables to determine appropriate next hop

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MANET Routing Properties

Distributed operation No external network setup “self-configuring” Efficient when network topology is dynamic (frequent network

changes – links break, nodes come and go) And also:

Loop Freedom Sleep period operation Unidirectional link support Security

Quantitative Properties End-to-End data throughput Delays Route Acquisition time Out of order delivery (percentage)

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Types of protocols behaviour

Proactive protocols They determine routes independently from the traffic patterns Traditional protocols like link-state and distance-vector are proactive

Reactive protocols They create a route only if required

There are also hybrid solutions Aspects to take into consideration

Waiting time for getting a route Proactive protocols are typically faster Reactive protocols normally have a higher latency

Overhead for route discover and maintenance Proactive protocols typically have an higher overhead because they are

always updating routing tables Reactive protocols normally have a lower overhead because they add control

traffic only when necessary

The solution to adopt depends on the type of the data traffic and the type of mobility!

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10 manet Working Group

IETF WG: Mobile Ad-hoc Networks (manet) http://www.ietf.org/html.charters/manet-charter.html Additional MANET links:

http://www.ianchak.com/manet/ Additional information is available at:

http://tools.ietf.org/wg/manet

Purpose of MANET working group standardize IP routing protocol functionality suitable for wireless routing

application within both static and dynamic topologies with increased dynamics due to node motion or other factors.

Approaches are intended to be: relatively lightweight in nature suitable for multiple hardware and wireless environments, and address

scenarios MANETs are deployed at the edges of an IP infrastructure hybrid mesh infrastructures (e.g., a mixture of fixed and mobile routers)

should also be supported by MANET specifications and management features.

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http://www.ietf.org/html.charters/manet-charter.html

http://www.ianchak.com/manet/

http://tools.ietf.org/wg/manet

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10 manet Working Group

The group is pursuing a reactive and a proactive protocol. On the charter page these are called RMP and PMP respectively. Proactive MANET Protocol (PMP) Reactive MANET Protocol (RMP)

In practice the reactive protocol is DYMO and the proactive is OLSRv2.

If significant commonality between RMP and PMP modules is observed, the WG may decide to go with a converged approach.

Both IPv4 and IPv6 will be supported. Routing security requirements and issues will also be

addressed. The MANET WG will also develop a scoped forwarding protocol

that can efficiently flood data packets to all participating MANET nodes.

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10 Proposed protocols Here: http://en.wikipedia.org/wiki/Ad_hoc_protocol_list

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10 Classification of Ad Hoc Routing Protocols

Routing protocols for ad hoc wireless networks

Based on routing information update

mechanism

Based on the use of temporal information for

routing

Based on topology information

Based on utilization of specific resources

Proactive(table-driven or

link-state)Hybrid

Path selection using past

history

Path selection using prediction

• DSDV• OLSR• HSR

• ZRP

• DSDV• DSR• AODV• DYMO

• FORP

Reactive(table-driven)

• DSR• AODV• DYMO

Flat routing Hierarchical routing

• DSDV• DSR• AODV• DYMO

• HSR

Energy-aware routing

Geographical routing

• PAR • GPSR

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10 Most relevant routing protocols D. Johnson, D. Maltz, and Y-C. Hu.

The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks (DSR),RFC 4728, February 2007. http://tools.ietf.org/html/rfc4728

C. Perkins, E. Belding-Royer, and S. Das. Ad hoc On-Demand Distance Vector (AODV) Routing. RFC 3561, July 2003. http://tools.ietf.org/html/rfc3561

I. Chakeres, C. Perkins. Dynamic MANET On-demand (DYMO) Routing. draft-ietf-manet-dymo-17, March 2009. http://tools.ietf.org/html/draft-ietf-manet-dymo-17

T. Clausen et al. The Optimized Link-State Routing Protocol version 2. draft-ietf-manet-olsrv2-08, March 2009. T. Clausen and P. Jacquet.

Optimized Link State Routing Protocol (OLSR). RFC 3626, October 2003. http://www.ietf.org/rfc/rfc3626.txt

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10 Flooding as a basic mechanism 1/615

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Node that just received a frame

Frame broadcasted

Node that just forwarded a frame

destination

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possible collision!!


Frame broadcasted


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Receives the frame but does not forward it. Already done


Frame broadcasted


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Receives the frame form J and from K (which are mutually hidden) possible collision


Frame broadcasted


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D does not forward it because is the final destination


Frame broadcasted


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Flooding is over!


Frame broadcasted


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1021 Flooding as a basic mechanism: a few

considerations Many protocols use limited flooding of the control

packets. Control packets are used to discover the routes.

Advantage: Simplicity Disadvantage: Overhead possibly very high

The established routes are then used to send packets of data.

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1023 Dynamic Source Routing (DSR)

For networks of medium size (200 nodes), admits high speeds When node S wants to send a packet to node D, but does not

have a route to D, begins a route discovery process. Source node S floods Route Request (RREQ) packets Each node adds its own id when it forwards a RREQ.

Use of the “send buffer”

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10 Route Request in DSR, 1/524

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destination

Node that just received a RREQ

IDs list added to the RREQ

Node that just forwarded an RREQ

[X,Y]

Y

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Possible collision!!




[X,Y]

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RREQ is not forwarded




[X,Y]

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Possible collision




[X,Y]

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[X,Y]

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10 Route Reply

Destination D, when receiving the first RREQ send a Route Reply (RREP)

RREP is sent using the route obtained by reversing the one that is in the received RREQ

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RREP [S,E,F,J,D]

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10 Route Reply en DSR

Route Reply can be sent by reversing the route in Route Request (RREQ) only if links are guaranteed to be bi-directional To ensure this, RREQ should be forwarded only if it received on a link

that is known to be bi-directional

If unidirectional (asymmetric) links are allowed, then RREP may need a route discovery for S from node D Unless node D already knows a route to node S If a route discovery is initiated by D for a route to S, then the Route

Reply is piggybacked on the Route Request from D.

If IEEE 802.11 MAC is used to send data, then links have to be bi-directional (since Ack is used)

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10 Dynamic Source Routing (DSR)

Node S on receiving RREP, caches the route included in the RREP

When node S sends a data packet to D, the entire route is included in the packet header hence the name source routing

Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded

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10 Data Delivery in DSR32

Packet header size grows with route length

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DATA [S,E,F,J,D]

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1033 DSR Optimization: Route Caching (1/2)

Each node caches a new route it learns by any means When node S finds route [S,E,F,J,D] to node D, node S also learns route

[S,E,F] to node F When node K receives Route Request [S,C,G] destined for node, node K

learns route [K,G,C,S] to node S When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route

[F,J,D] to node D When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D A node may also learn a route when it overhears Data packets

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10 DSR Optimization: Route Caching (2/2)

When node S learns that a route to node D is broken, it uses another route from its local cache, if such a route to D exists in its cache. Otherwise, node S initiates route discovery by sending a route request

Node X on receiving a Route Request for some node D can send a Route Reply if node X knows a route to node D

Use of route cache can speed up route discovery can reduce propagation of route requests

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10 Route Error (RERR) J sends a route error to S along route

J-F-E-S when its attempt to forward the data packet S (with route SEFJD) on J-D fails

Nodes hearing RERR update their route cache to remove link J-D

Each node is responsible for confirming that the link can be used to transmit data. Ack del MAC (p.ej., 802.11) Passive acks DSR-specific ACK

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10 DSR additional techniques

“Expading ring” technique playing with the TTL of the packets “non propagating” Route Request

“Route salvaging” technique for route maintenance Dynamic substitution of routes for intermediate ndoes

“Automatic route shortening” technique for routes optimization Based on “gratuitous” Route Reply

The “flows”

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10 DSR: advantages and disadvantages Routes maintained only

between nodes who need to communicate reduces overhead of route

maintenance

Route caching can further reduce route discovery overhead

A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches

Packet header size grows with route length due to source routing

Flood of route requests may potentially reach all nodes in the network

Care must be taken to avoid collisions between route requests propagated by neighboring nodes insertion of random delays before

forwarding RREQ

Increased contention if too many route replies come back due to nodes replying using their local cache Route Reply Storm problem Reply storm may be eased by

preventing a node from sending RREP if it hears another RREP with a shorter route

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1039 First Back to basics : Distance Vector protocol

Basic Routing Protocol known also as Distributed Bellman-Ford or RIP

Every node maintains a routing table all available destinations the next node to reach the destination the number of hops to reach the destination

Periodically send table to all neighbors to maintain topology Bi-directional links are required!

Thanks to Raoul Reuter

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1040 First Back to basics : Distance Vector -> tables

CDest. Next Metric …

A A 1

B B 0

C C 2

Dest. Next Metric …

A A 0

B B 1

C B 3

1 2


A B 3

B B 2

C C 0

BA


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1041 First Back to basics : Distance Vector -> update

(A, 1)(B, 0)(C, 1)

(A, 1)(B, 0)(C, 1)

CDest. Next Metric …

A A 1

B B 0

C C 1


A A 0

B B 1

C B 3 2

1 21


A B 3 2

B B 1

C C 0

BA

B broadcasts the new routing information to his neighbors

Routing table is updated


A change occurs so…

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1042 First Back to basics : Distance Vector -> new

node

(D, 0)

(A, 2)(B, 1)(C, 0)(D, 1)

(A, 1)(B, 0)(C, 1)(D, 2)

C1 1

BA D1

broadcasts to update tables of C, B, A with new entry for D


A B 2

B B 1

C C 0

D D 1


A A 1

B B 0

C C 1

D C 2


A A 0

B B 1

C B 2

D B 3


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1043 First Back to basics : Distance Vector

Broken Link and consequent Loops…

(D, 2)(D, 2)

C1 1

BA D1


… … …

D B 3


… … …

D C 2


… … …

D B 3

C1 1

BA D1

Dest.c Next Metric …

… … …

D C 2


… … …

D B 3


… … …

D B 1


… … …

D D


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1044 First Back to basics : Distance Vector

… create the “Count to Infinity” problem

(D,2)

(D,4)

(D,3)

(D,5)

(D,2)

(D,4)

C1 1

BA D1


… … …

D B 3, 5, …


… … …

D B 3, 5, …

Dest.c Next Metric …

… … …

D C 2, 4, 6…


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10Ad Hoc On-Demand Distance Vector Routing

(AODV) DSR includes source routes in packet headers. Resulting large headers can sometimes degrade performance

particularly when data contents of a packet are small

AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain routes

AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate

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10 AODV

Route Requests (RREQ) are forwarded in a manner similar to DSR

When a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source AODV assumes symmetric (bi-directional) links

When the intended destination receives a Route Request, it replies by sending a Route Reply

Route Reply travels along the reverse path set-up when Route Request is forwarded

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10 Route Request in AODV47

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RREQ broadcast


destination

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RREQ broadcast


Inverse link

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RREQ broadcast


Inverse link

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RREQ broadcast


Inverse link

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10 Forward Path Setup in AODV53

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10 AODV Concepts (2)

Local HELLO messages are used to determine local connectivity Can reduce response time to routing requests Can trigger updates when necessary

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

Every node maintains two counters Node sequence number Broadcast ID

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10 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_iddest_addr

type flags hopcntresvd

dest_sequence_#source_addr

source_sequence_#

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Sequence numbers Source sequence indicates “freshness” of reverse route to the source Destination sequence number indicates freshness of route to the

destination Every neighbor receives the RREQ and either …

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

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

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If a node cannot respond to the RREQ The node increments the hop count The node saves information to implement a reverse path set up (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 collection)

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10 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)

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10 AODV Example (2)

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

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10 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 1 Increment hop_cnt in the RREQ packet

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10 AODV Example (4)

RREQ reaches Node 6, which knows a route to 7 Node 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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10 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_addrtype flags hopcntrsvd

dest_sequence_#source_addr

lifetime

prsz

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10 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, or destination_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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10 AODV Example (5)

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

dest_sequence_# in RREQ) hop_cnt = 1

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10 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 1 Increments hop_cnt in the RREP packet

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10 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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10 AODV Route Maintenance

Route changes can be detected by… Failure of periodic HELLO packets Failure or disconnect indication from the link level Failure of transmission of a packet to the next hop (can detect 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 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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10 Notification about a link break

A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry

When the next hop link in a routing table entry breaks, all active neighbors are informed

Link failures are propagated by means of Route Error messages, which also update destination sequence numbers When node X is unable to forward packet P (from node S to node D) on

link (X,Y), it generates a RERR message Node X increments the destination sequence number for D cached at

node X The incremented sequence number N is included in the RERR When node S receives the RERR, it initiates a new route discovery for D

using destination sequence number at least as large as N

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10 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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10 DYMO vs AODV

Answers by Ian Chakeres to the question: “could you briefly explain what are the differences between DYMO and AODV “ 8 Mar 2005

There are several differences between AODV, AODV-bis, DSR and DYMO. To list just a few.

New packet format. Generic packet handling. Unsupported element handling. Optional path accumulation. Much more.

23 Mar 2006 DYMO is a simpler version of AODV. DYMO is easier to implement and

has lower requirements (in terms of memory, code, etc.) than AODV. DYMO is close to what has been implemented for sensor networks, such as tinyAODV. AODV is no longer being explored in the MANET WG.

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10 DYMO71

DYMO – Reactive Protocol like AODV, but with path accumulation feature

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10 DYMO Path accumulation

Path accumulation definitely reduces the number of RREQs Topology information is discovered much more quickly However, it also increases the packet size

Packet size is often a burden that negates some of the benefit of path accumulation

And, the benefit is reduced if newly discovered routes are not used before being purged from the routing cache

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10 First Back to basics : Link-State Algorithms (1)

Each node shares its link information so that all nodes can build a map of the full network topology

Link information is updated when a link changes state (goes up or down) Link state determined by sending small “hello” packets to neighbors

Given full topology information, a node can determine the next best hop or a route from the source

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Assuming the topology is stable for a sufficiently long period, all nodes will have the same topology information

A

B

C DA-BLink

B-CC-D

A-BLink

B-CC-D

A-BLink

B-CC-D

A-BLink

B-CC-D

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Nodes A and C propagate the existence of link A-C to their neighbors and, eventually, to the entire network

A

B

C D

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-BLink

B-CC-D

A-C

A-C A-C

A-C

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10 Optimized Link State Routing (OLSR)

Proactive scheme based on the link-state mechanism. Each node periodically floods status of its links Each node re-broadcasts link state information received from its

neighbor Each node keeps track of link state information received from other

nodes Each node uses above information to determine next hop to each

destination

The overhead of flooding link state information is reduced by requiring fewer nodes to forward the information

Does not require modifying the structure of the IP packets

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10 OLSR v2

Compared to OLSRv1, OLSRv2 retains the same basic mechanisms and algorithms, while providing an even more flexible signaling framework and some simplification of the messages being exchanged.

OLSRv2 takes care to accommodate both IPv4 and IPv6 addresses in a compact fashion.

The message exchange format has been factored out to an independent specification Clausen, T., Dean, J., Dearlove, C., and C. Adjih, "Generalized MANET

Packet/Message Format", work in progress. The OLSRv2 neighborhood discovery protocol using HELLO

messages has been factored out to an independent specification Clausen, T., Dean, J., and C. Dearlove, "MANET Neighborhood Discovery

Protocol (NHDP)", work in progress.

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10 LSR vs. OLSR The overload of broadcasting the

status information on the links is reduced by limiting the number of nodes which forward this information A broadcast from node X is

forwarded only by its multipoint relays

The multipoint relays of X are its neighbors chosen so that every two-hops neighbors of X is a one-hop neighbors of at least one of its multipoint relay

Each node periodically transmits the list of its neighbors so that all nodes can know which are their two-hops neighbors, therefore being able to choose their multipoint relays

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11 broadcasts are needed to spread the message up to three hops away

24 broadcasts are needed to spread the message up to three hops away

Sending node

Sending node

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10 Terminology Nodes can have various OLSR

interfaces, each with its own IP address Each node is assigned a unique

reference IP (‘main address’) neighbor: x is a neighbor of y if y can

receive x signal 2-hop neighbor: a node whose

signal is received by its neighbor. strict 2-hop neighbor:

a 2-hop neighbor which is not the node itself or a neighbor of the node, and in addition is a neighbor of a neighbor, with willingness different from WILL_NEVER, of the node.

multipoint relay (MPR): A node selected by its neighbor x,

to forward all the broadcast messages received from x, if it is not a duplicate message and if life-time is >1

multipoint relay selector (MS) A node that selected its neighbor x

as a MPR

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M

X YZ

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10 Neighbor sensing Each node periodically broadcasts

Hello messages: List of neighbors with bi-directional

link List of other known neighbors.

Hello messages permit each node to learn topology up to 2 hops

Based on Hello messages each node selects its set of MPR’s

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10 MPR selection algorithm

Each point u has to select its set of MPR. Goal: select in the 1-neighborhood of u (N1(u)) a set of nodes

as small as possible which covers the whole 2-neighborhood of u (N2(u)), in two steps : Step 1: Select nodes of N1(u) which cover isolated points of N2(u).

(That we call MPR1(u).) Step 2: Select among the nodes of N1(u) not selected at the first step,

the node which covers the highest number of points (not already covered) of N2(u) and go on till every points of N2(u) are covered.

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10 MPR selection algorithm : example83

u

First step: select nodes in N1(u) which cover « isolated points » of N2(u).

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10 MPR selection algorithm : example84

u

Second step: Consider in N1(u) only points which are not already selected at the first step MPR1(u) and points in N2(u) which are not covered by the MPR1(u). While there exists points in N2(u) not covered by the selected MPR, select in N1(u), the node which covers the highest number of non-covered nodes in N2(u).

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10 MPR selection algorithm: example; final result85

u

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10 Multipoint Relay Selector Set

The multipoint relay selector set for Node N, MS(N), is the set of nodes that choose Node N in their multipoint relay set Only links N-M, for all M such that NMS(M) will be advertised in control

messages

MS(3) = {…, 4, …}MS(6) = {…, 4, …}

(Assuming bidirectional links)

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10 HELLO Messages (1)

Each node uses HELLO messages to determine its MPR set All nodes periodically broadcast HELLO messages to their one-

hop neighbors (bidirectional links) HELLO messages are not forwarded

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7

HELLO: NBR(4) = {1,3,5,6}

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Using the neighbor list in received HELLO messages, nodes can determine their two-hop neighborhood and an optimal (or near-optimal) MPR set

A sequence number is associated with this MPR set Sequence number is incremented each time a new set is calculated

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At Node 4:NBR(1) = {2}NBR(3) = {2,5}NBR(5) = {3,6}NBR(6) = {5,7}

MPR(4) = {3,6}

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Subsequent HELLO messages also indicate neighbors that are in the node’s MPR set

MPR set is recalculated when a change in theone-hop or two-hop neighborhood is detected

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HELLO: NBR(4) = {1,3,5,6}, MPR(4) = {3,6}

MS(6) = {…, 4,…}

MS(3) = {…, 4,…}

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10 TC Messages

Nodes send topology information in Topology Control (TC) messages List of advertised neighbors (link information) Sequence number (to prevent use of stale information)

A node generates TC messages only for those neighbors in its MS set Only MPR nodes generate TC messages Not all links are advertised

A nodes processes all received TC messages, but only forwards TC messages if the sender is in its MS set Only MPR nodes propagate TC messages

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10 OLSR Example (1)

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MPR(1) = { 4 }MPR(2) = { 3 }MPR(3) = { 4 }MPR(4) = { 3, 6 }MPR(5) = { 3, 4, 6 }MPR(6) = { 4 }MPR(7) = { 6 }

MS(1) = { }MS(2) = { }MS(3) = { 2, 4, 5 }MS(4) = { 1, 3, 5, 6 }MS(5) = { }MS(6) = { 4, 5, 7 }MS(7) = { }

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10 OLSR Example (2)

Node 3 generates a TC message advertising nodes in MS(3) = {2, 4, 5}

Node 4 forwards Node 3’s TC message sinceNode 3 MS(4) = {1, 3, 5, 6}

Node 6 forwards TC(3) since Node 4 MS(6)

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TC(3) = <2,4,5>

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10 OLSR Example (3)

Node 4 generates a TC message advertising nodes in MS(4) = {1, 3, 5, 6}

Nodes 3 and 6 forward TC(4) since Node 4 MS(3) and Node 4 MS(6)

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TC(4) = <1,3,5,6>

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10 OLSR Example (4)

Node 6 generates a TC message advertising nodes in MS(6) = {4, 5, 7}

Node 4 forwards TC(6) from Node 6 and Node 3 forwards TC(6) from Node 4

After Nodes 3, 4, and 6 have generated TC messages, all nodes have link-state information to route to any node

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TC(6) = <4,5,7>

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10 OLSR Example (5)

Given TC information, each node forms a topology table

A routing table is calculated from the topology table

Note that Link 1-2 is not visible except to Nodes 2 and 3

TC(3) = <2,4,5>

TC(4) = <1,3,5,6> TC(6) = <4,5,7>1

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6

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4

Dest Next Hops1 4 22 2 14 4 15 5 16 4 (5) 27 4 (5) 3

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10 Routing table

All nodes manage a routing table Its structure is:

1. R_dest_addr R_next_addr R_dist R_iface_addr2. R_dest_addr R_next_addr R_dist R_iface_addr3. ,, ,, ,, ,,

Each entry indicates that node R_dest_addr is R_dist hops away, and the first hop is through R_next_addr. This node can be reached through the local interface R_iface_addr

There is an entry for each destination in the network The table is updated each time a change is detected in:

the link set, the neighbor set, the 2-hop neighbor set, the topology set, the Multiple Interface Association Information Base,

The table is built using a shortest path algorithm

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10LUNAR (Lightweight Underlay Network Ad hoc

Routing) Instead of having routing protocol logic that actively

maintains and repairs existing routing paths, LUNAR always establishes paths from scratch.

LUNAR floods the network every 3 s for discovering a route. During the 3 s interval, all data packets are shipped over the

same path and no attempts are made to discover lost packets or to monitor link changes.

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10 Zone Routing Protocol (ZRP)

Zone routing protocol combines Proactive protocol: which pro-actively updates network state and

maintains route regardless of whether any data traffic exists or not Reactive protocol: which only determines route to a destination if there

is some data to be sent to the destination All nodes within hop distance at most d from a node X are

said to be in the routing zone of node X All nodes at hop distance exactly d are said to be peripheral

nodes of node X’s routing zone Intra-zone routing: Pro-actively maintain state information for

links within a short distance from any given node Routes to nodes within short distance are thus maintained proactively

(using, say, link state or distance vector protocol) Inter-zone routing: Use a route discovery protocol for

determining routes to far away nodes. Route discovery is similar to DSR with the exception that route requests are propagated via peripheral nodes.

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10ZRP: Example with

Zone Radius = d = 210

0

SCA

EF

B

D

S performs routediscovery for D

Denotes route request

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10 ZRP: Example with d = 2101

SCA

EF

B

D


Denotes route replyE knows route from E to D, so route request need not beforwarded to D from E

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10 ZRP: Example with d = 2102

SCA

EF

B

D


Denotes route taken by Data

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10 Geographic routing - GeoNet

Geographic routing applied specifically to VANETs. Uses the geographic position and movement information of vehicles to route data packets.

Each node maintains a location table including location related information for itself and a list of its neighbouring nodes.

Position information, including speed and direction, exchanged in beacon packets

Forwarding uses Greedy Perimeter Stateless Routing (GPSR) protocol

Communication modes: GeoUnicast – from a node to a known location GeoAnyCast – from a node to any node in a geographic area GeoBroadCast – from a node to all nodes in a geographic area Topo-Broadcast – from a node to all nodes a given number of hops away

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10 Geographical Routing - Basics104

Next Hop SelectionGiven a DESTINATION, the node that is holding the message selects the next hop according to 1) Its own position2) The position of the destination node3) The position of its neighbors (nodes in the Knowledge Range)DIFFERENT FORWARDING RULES ARE POSSIBLE!

DESTINATION

MESSAGE HOLDER

KNOWLEDGE RANGE

Thanks to: Peter Scheuermann Northwestern University

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10 GPSR: Greedy Perimeter Stateless Routing

Key Assumptions: Nodes (routers) know their location

GPS, beacon, tri/multi-lateration… (Roughly) Planar Topologies Maybe: Registration/Lookup service mapping nodes to location

Sources can determine the addresses of their destinations and encode them as part of the packet(s).

Queries use the same “address-book”(Implicit: Unit-disk graph model of communication range…)

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10 GPSR - basics106

D X

node D

Node X receives a packet, for which the destination is D

Of all the X’s neighbors, Y is closest to D=> “greedy” forwarding (decreasing the total distance)

Y


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10 GPSR – basics

Q: What if the neighborhood changes (e.g., nodes deplete their energy; new nodes enter the region; …)? Periodically, each node transmits a beacon to the common, broadcast

MAC address, containing (ID, location). Hence, the neighbors can update their data…

If the time during which a beacon has not been received from a given neighbor exceeds a pre-defined time-out interval, assume failure and delete it from neighborhood-table.

Two four-Bytes fields (float) for each of X and Y coordinates… NOTE: this is pro-active… To save on communication for beaconing, location info can be

piggy-backed on the data packets All? Which ones?

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10 GPSR – Problem(s) with the ”greedy”…108

XA B

DD

For the given network, assume thatX receives a packet to be forwardedto the node D.

IF A & B are the only ones inIts communication range, since XIs closer to D than both of themÞ the “pure” GPSR would NOTsend the packet !!!

Hence, one type of problems are due tothe, so called, VOID regions


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10 GPSR – Problem(s) with the ”greedy”…109

XA B

D

C E

F G

Solution to voids:- Travel around the perimeter of the void,using as “road-segments” the edges between the nodes (view communication graph as a node) - Eventually/hopefully, get closer tothe desired destination…(e.g., X->B->E->G->D)

OK, so this is kind’a graph-theoretic…Ergo, it brings another problem: howAre edges that are intersecting to be treated (are they having an actual vertex)Solution: Enforce the PLANARITY…


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1011

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GPSR – Problem(s) with the ”greedy”…

Desideratum: reduce the number of “active” neighbors, while preserving the connectivity of the network as a whole. This should be done in a manner to ensure min. amount of “links” to be

traveled for whatever purpose needed…

Two basic geometric techniques used for making a given graph planar, while ensuring that all the nodes that the connectivity is the same, with respect to the initial connectivity under the unit-disk model: Relative Neighborhood Graph (RNG) Gabriel Graph (GG)


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1011

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GPSR – Planarization of Graphs:

w

vu

RNG:An edge exists between u and v, if their distance isless than the max[(u,w),(v,w)] for any other such vertex w

e.g., no “witnesses” in the luna

w

vu

GG: An edge exists between u and v, if no other vertex is inside the circle whose diameter is uv

e.g., no “witnesses” inside the circle


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10 Quantitative Observations…112

RNG GG


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10 Back to GPRS113

OK, so given an initial network, assume that we are done withRNG-ization or GG-ization…

The typical packet can either:forward greedily;

orforward around perimeter…

For the purpose of forwarding around the perimeter, the GPSR packet header has the following fields:…

D –destination location;Lp – Location in which the packetentered the “perimeter” mode;Lf – Location on xV in which the packet entered current face (TBE);e0 – first edge traversed on the current edge;M – packet mode (G/P)


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1011

4 So, just what is “walk around perimeter”???AKA Face Routing…

And proceed “recursively”Thanks to: Peter Scheuermann Northwestern University

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10 GPSR115

Face: planar region bounded by the edges in a given graph (can be “open”)

X

D

When void encountered;- “draw” the line XD;- Pick the face at X intersected by XD;- Select the edge on that face -> LHS; -Traverse the edges on the boundaryof that face -> RHS;-At any point, if non-void (i.e., greedy-possible), do greedy;

NOTES:1. Cycles can be detected (recall the header data)2. Cycles can only happen when X and D are NOT in one connected component…


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1011

6

Some Issues of GPSR…

What if mobility is part of the game? MAC failure feedback…

Promiscuous use of network interface Disable MAC address filtering (reason: every packet carries location

data…) How realistic is the assumption about symmetric links (in turn,

how good is the RNG/GG-ization of the connectivity graph)? Planarity of the graph?

Nodes move (in/out), deplete baterries => batch or incremental updates?


redes inalámbricas – tema 3. mobile ad hoc networks

Documents

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network3redes inalmbricas

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