Mn 12 Routing Protocols for Adhoc Networks 12-38 Slides

8/13/2019 Mn 12 Routing Protocols for Adhoc Networks 12-38 Slides

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Routing Protocols for Ad-Hoc Wireless Networks

Lecture#12


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Traditional RoutingA routing protocol sets up a routing table in routers

A node makes a local choice depending on global topology

Routing Table AT 1

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Traditional Distance Vector Routing

Based on periodic exchanges of neighbor information(connectivity and cost)

Changes at one node propagate slowly through the network

Strategies needed to avoid the count to infinity problem(problems with fast topology changes) Poisoned-reverse

Split-horizon

Potential problems Unreachable regions

Routing loops

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Tables

CDest. Next Metric

A A 1B B 0C C 2

Dest. Next Metric A A 0B B 1C B 3

1 2

Dest. Next Metric A B 3B B 2C C 0

B A

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(D, 0)

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

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

New Node

C1 1

B A D1

broadcasts to updatetables of C, B, A with

new entry for D

Dest. Next Metric A B 2B B 1C C 0D D 1

Dest. Next Metric A A 1B B 0C C 1D C 2

Dest. Next Metric A A 0B B 1C B 2D B 3

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Broken Link

C1 1

B A D1

Dest.c Next Metric D C 2

Dest. Next Metric D B 3

Dest. Next Metric D B 1

Dest. Next Metric D D

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(D,2)

(D,4)

(D,3)

(D,5)

(D,2)

(D,4)

Count to Infinity

C1 1

B A D1

Dest. Next Metric D B 3, 5,

Dest. Next Metric D B 3, 5,

Dest.c Next Metric D C 2, 4, 6

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Interaction with Static Internet

Two network types Transit network: a datagram can enter and then leave the network

Stub network: the network is either the sink or source for all datagrams

MANETs are envisioned as being only stub network (at least fornow) Reduces power and processing demands

Simplifies routing interaction

Mobile IP allows connectivity with the traditional static Internet

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MANET vs.. Traditional Routing

Traditional routing algorithms are likely to be Inefficient due to slow convergence times (e.g., using distance vector algorithms

as in RIP)

Non-functional due to large amounts of data or inability to deal with asymmetriclinks

MANET routing must rely on data link information, not just networklayer updates

Link layer determines connectivity and quality of links

Centralized approaches are too slow and not robust enough for MANET

All (or almost all) nodes in a MANET may be routersLong-lived circuits cannot be used in MANETs

Path length (hop count) may not be the best metric for routing inMANETs

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Issues in Designing a Routing Protocol for AdHoc Wireless Network

Mobility Frequent path loss due to the movement of intermediate nodes or

the end nodes Requires faster convergence time

Wired routing protocols have slow convergence, therefore, notsuitable for ad hoc networks

Limited bandwidth Imposes constraint on routing protocols in maintaining the

topological information Frequent changes in topology makes it difficult to maintain a

consistent view of the topological information Require more control overhead which results in more BW wastage

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Issues in Designing a Routing Protocol for AdHoc Wireless Network

Error-Prone Shared Broadcast Radio Channel Wireless links have time varying characteristics in terms of link capacity

and link error probability

Requires that routing protocols to interact with the MAC layer to find an

alternate routes through better quality links Transmission results in collision of data packets and control packets

Required to find paths with less congestion

Hidden and exposed terminal problems

Collision of data and control packets and under utilization of BW isattributed to hidden and exposed node problems

Resource constraints Battery life and processing power

Routing protocols must optimally used these resource14


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Qualitative Characteristics of an Ideal Routing Protocol

Fully distributed Centralized routing involves high control overhead and are not scalable Distributed routing more tolerant Avoids the risk of single point failure

Adaptive to frequent topology changesMinimum route computation and maintenances

Localized Global state involves a huge state propagation control overhead

Loop freeFree from stale routeUnidirectional link supportPacket collision minimum by limiting the broadcastConvergence must be quickOptimally use the resourcesEach node should try to store the stable route information only

Provide certain level of QoS 15


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Quantitative Performance MetricsEnd-to-end throughput

External measure of routing effectiveness

End-to-end delay External measure of routing effectiveness

Route acquisition time

Of particular concern with on-demand routing algorithmsPercentage of out-of-order datagram deliveries

Affects performance of higher-layer protocols like TCP

Efficiency (internal measures) Ratio of average number of data bits transmitted to average number of data

bits delivered Ratio of average number of control bits transmitted to average number of data

bits delivered Ratio of average number of control and data packets transmitted to average

number of data packets delivered16


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Performance Factors

Network size Number of nodes

Network connectivity Average degree of a node

Rate of change of the topology Speed at which the network topology is changing

Link capacity Effective data rate (bits/second) after affects of packet loss, coding, multiple access

overhead, etc

Fraction of unidirectional links

Traffic patterns Uniform versus non-uniform destinations Bursty versus non-bursty traffic

Mobility Model for node mobility

Fraction and frequency of sleeping nodes 17


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Classification of Routing Protocols

Based in routing information update mechanisms

Proactive or table driven protocols Reactive or on-demand routing protocols Hybrid routing protocols

Based on the use of temporal information on routing Use the temporal information regarding the lifetime of wireless links

and the lifetime of the paths selected Routing protocols using past temporal information

Use past status of the link or the status of the link at the time of routing

Routing protocols that use future temporal information Life time of wireless links, remaining battery life, prediction of location,

and prediction of link availability

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Based on the routing topology

Internet use hierarchical routing topology in order to reduce the state informationmaintained at the core routers

Flat topology routing protocols Use flat addressing scheme Presence of a unique addressing scheme in an ad hoc network

Hierarchical topology routing protocols Make use of a logical hierarchy in the network and an associated addressing scheme Could be based on geographical information or it could be based on hop distance

Based on the utilization of specific resource

Power aware routing Aims at minimizing the battery power, routing decisions are based on either globallyor locally

Geographical information assisted routing Reduce the control overhead by effectively utilizing the geographical information

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Based in Routing InformationUpdate Mechanisms

Table Driven Routing Protocols

(Proactive Protocols)DSDV , WRP, CGSR, STAR


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Protocol Trade-offs

Proactive protocols Always maintain routes

Little or no delay for route determination

Consume bandwidth to keep routes up-to-date

Maintain routes which may never be used

Reactive protocols Lower overhead since routes are determined on demand

Significant delay in route determination

Employ flooding (global search) Control traffic may be bursty

Which approach achieves a better trade-off depends on thetraffic and mobility patterns !!

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Destination Sequenced Distance Vector (DSDV)

Each route table at each of the nodes, lists all available destinationsand the number of hops to eachContains the shortest distance and the first node on the shortest

path to every other node in the networkEach entry is tagged with a sequence number that is originated by

the destination nodeEach node periodically transmits updates These updates indicate which nodes are accessible from each node and

number of hops to reach them

It incorporates table updates with increasing sequence number tagsto prevent loops, to counter the count-to-infinity problems, and forfaster convergenceRouting information is advertised by broadcasting or multicasting

Packets are transmitted periodically and incrementally 23


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Route Advertisements

Data is kept for a length of time between the arrival of the first andthe arrival of the best route Advertisement of possibly unstable routes is delayed to reduce the number of

rebroadcasts (damping fluctuations)

DSDV requires each mobile node to advertise its own routing table

to each of its current neighborsEntries may change fairly dynamicallyEach mobile computer agrees to relay data packets to othercomputers upon request

Mobile computer may exchange data with any other computer in agroup Even if the target is not within the range of direct communication

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Route Establishment in DSDV

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Route Advertisements

Advertise to each neighbor own routing information Destination Address Metric = Number of Hops to Destination Destination Sequence Number Other info (e.g. hardware addresses)

Rules to set sequence number information On each advertisement increase own destination sequence

number (use only even numbers) If a node is no more reachable (timeout) increase sequencenumber of this node by 1 (odd sequence number) and setmetric = .

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Route Table Entry Structure

Data broadcast by each mobile computer contains itsnew sequence number and Destinations address Number of hops required to reach destination

Sequence number of the information received regarding thatdestination

Within the header of the packet, the transmitted routetables will also contain Hardware address of transmitting node Network address of transmitting node

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Table Entries

Sequence number originated from destination Ensures loop freeness

Install time when entry was made

Used to delete stale entries from tableStable data pointer to a table holding information on how stablea route is Used to damp fluctuations in network

Destination Next Metric Seq. Nr Install Time Stable Data

A A 0 A-550 001000 Ptr_A

B B 1 B-102 001200 Ptr_B

C B 3 C-588 001200 Ptr_C

D B 4 D-312 001200 Ptr_D

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Route Table Entry Structure

Routes with more recent sequence numbers are always preferred as the basis of forwarding decisions

But they are not necessarily advertised

Problem One way links

Receiving a packet does not indicate the existence of path back to thatneighbor

To avoid one way links No mobile node inserts routing information received from a

neighbor unless that neighbor shows that it can receive packetsfrom the mobile node

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Responding to Topology Change

Mobile nodes cause broken links as they move Broken link is described by a metric of

Any route through the broken link is immediately assignedan and an updated sequence number Sequence number is incremented by one Information describing a broken link is the only scenario in which

sequence number is generated by any node other than destination

Such a route change is immediately disclosed in broadcastrouting information

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(D, 0, D-000)

DSDV (New Node)

CB A DDest. Next Metric Seq.

A A 0 A-550B B 1 B-104C B 2 C-590

Dest. Next Metric Seq. A A 1 A-550B B 0 B-104C C 1 C-590

Dest. Next Metric Seq. A B 2 A-550B B 1 B-104C C 0 C-590D D 1 D-000

1. D broadcast for first timeSend Sequence number D-000

2. C inserts entry for D withsequence number D-000, then

immediately broadcast own table

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(A, 2, A-550)(B, 1, B-102)(C, 0, C- 592 )(D, 1, D-000)

(A, 2, A-550)(B, 1, B-102)(C, 0, C- 592 )(D, 1, D-000)

DSDV (New Node cont.)

CB A DDest. Next Metric Seq.

A A 1 A-550B B 0 B-102C C 1 C-592D C 2 D-000

Dest. Next Metric Seq. A A 0 A-550B B 1 B-104C B 2 C-590

Dest. Next Metric Seq. A B 2 A-550B B 1 B-102C C 0 C-592D D 1 D-000

3. C increases its sequencenumber to C-592 then

broadcasts its new table.4. B gets this new information

and updates its table.

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(D, 2, D-100)(D, 2, D-100)

DSDV (no loops, no count to infinity)

CB A D1

Dest.c Next Metric Seq. D C 2 D-100

Dest. Next Metric Seq. D B 3 D-100

Dest. Next Metric Seq. D D D-101

1. Node C detects broken Link:-> Increase Seq. Nr. by 1

(only case where not the destinationsets the sequence number -> odd

number)

2. B does its broadcast-> no affect on C (C knows that Bhas stale information because C hashigher seq. number for destination D)

-> no loop-> no count to infinity

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(D, , D-101)(D, , D-101)

DSDV (Immediate Advertisement)

CB A DDest.c Next Metric Seq.

D C 3 D-100



Dest. Next Metric Seq. D D 1 D-100

D D D-101

1. Node C detects broken Link:-> Increase Seq. Nr. by 1

(only case where not the destinationsets the sequence number -> odd

number)

3. Immediate propagationB to A:

(update information has higherSeq. Nr. -> replace table entry)

2. Immediate propagationC to B:

(update information has higherSeq. Nr. -> replace table entry)

Dest.c Next Metric Seq. ...D C 2 D-100

D C D-101

Dest. Next Metric Seq. ...D B 3 D-100

D B D-101

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Full/Incremental Update

Full Update Send all of the routing information from own table Requires multiple Network Protocol Data Units (NPDU)

A full update is scheduled When movements become frequent and the incremental update size

approaches the size of a NPDU To make the next incremental update smaller

Incremental Update Send only entries that have changed since last full Update Make it fit into one single packet

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Route Selection Criteria

On receiving a new routing information Information is compared to the information already available Metric is incremented by one New information is scheduled for advertisement

Any route with more recent sequence number is used Routes with older sequence numbers are discarded

A route with sequence number equal to an existing route is chosenif it has a better metric Older route may be discarded or stored as less preferable

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DSDV (Damping Fluctuations)

A

D

QP

10 Hops11 Hops

How to damp fluctuations Record last and avg. Settling Time of every Route in a

separate table. (Stable Data)Settling Time = Time between arrival of first route andthe best route with a given seq. no

A still must update his routing table on the first arrivalof a route with a newer seq. no., but it can wait toadvertising it. Time to wait is proposed to be 2*(avg.Settling Time)

Like this, fluctuations in larger networks can bedamped to avoid unnecessary advertisement, thussaving bandwidth

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Summary

Advantages Simple (almost like Distance Vector) Loop free through destination seq. numbers

No latency caused by route discovery

Disadvantages No sleeping nodes Bi-directional links required Overhead: most routing information never used Scalability is a major problem

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Source Tree Adaptive Routing(STAR) A bandwidth efficient routing protocol for ad hoc networks

A variation of table-driven routing protocols, with the LeastOverhead Routing Approach (LORA) as the key concept ratherthan the Optimum Routing Approach (ORA) that was employed

by the most of the table-driven routing protocols

LORA provides all the feasible paths with respect to some metricwhich may not be guaranteed optimal but with much less controloverheadEvery node broadcasts its source tree information

The set of links used by a router in its preferred path to a destination iscalled a source tree

Routers in STAR communicate their source routing trees toneighbors for all possible destinations

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Every node using its adjacent links, and the source tree broadcast by its neighbor links, builds a partial graph of its topologyDuring initialization, a node sends its update messages about newdestinations, the chances of routing loops, and costs of pathsexceeding a given thresholdHence, each node will have a path to every destination node The path, in most cases, would be sub-optimal

Such updates are communicated only when: Routers determine long-term loops can be created New destinations are found When a destination becomes unavailable

Source Tree Adaptive Routing(STAR)

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Source Tree Adaptive Routing(STAR)

The basic update unit used to communicate changes to source treesis the Link State Update (LSU)STAR uses sequence numbers to validate the LSUsA sequence number associated with a link consists of a counter that

can only be incremented by the head node (originator) of that linkAs LSUs for operational links never age out, there is no need forthe head node of a link to send periodic LSUs to update linkssequence number

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Path Finding ApproachWhen a nodes s has data packets to send to a particular destination

d, for which no path exists in its source-tree, its originates anupdate message to all its neighbors indicating the absence of a pathto dThis update message triggers another update message from a

neighbor which has path to d Node s retransmits the update message as long as it does not have a path to d with increasing intervals between successiveretransmissions

After getting the source-tree update from a neighbor, the node supdates its source-tree and, using this, finds a path to all nodes inthe networkThe data path contains information about the path to be traversed inorder to prevent the possibility of routing loop formation

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Route MaintenanceHandling the routing loops When an intermediate node k receives a data packet to destination d,

and one of the nodes in the packet`s traversed is present in node k` s path to the destination d, then it discards the packet and aRouteRepair update message is reliably sent to the node in the headof the route repair path

The route repair path corresponds to the path k to x, where x is the lastrouter in the data packet`s traversed path that is first found in the pathk to d, that belongs to the source tree of k

The RouteRepair packet contains the complete source tree of node k

and the traversed path of the packet When an intermediate node receives a RouterRepair update message,

it removes itself from the top of the route repair path and reliablysends it to the head of the route repair path

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STAR Exchanging Update MessagesUpdate messages exchange depends on the routing approach

used(ORA or LORA)For ORA to be supported in STAR, a router must send an updatemessage whenever its source tree changesFor LORA in STAR, a router reports updates to its source trees in

event of unreachable nodes, new destinations, loops or costexceeding a given thresholdIf the new source tree includes neighbors other than those presentin the source tree that was last updated, the router must send its

entire source tree in the updateIf the two source trees contain the same neighbors, the router sendsonly the updates needed to obtain the new tree from the old one

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STAR Impact of the Link LayerIf the underlying MAC protocol does not provide collision-free

transmission for reliable broadcasting, then in STAR, the router broadcasts to neighbors unreliablyA packet must specify the path it has traversedA router must send its update reliably to the neighbor that caused it

to change its source routing tree

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AdvantagesLow communication overhead among all the table-driven routing

protocolsThe use of LORA approach in this table-driven routing protocolreduces the average control overhead compared to several other on-demand routing protocols

Mn 12 Routing Protocols for Adhoc Networks 12-38 Slides

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