wireless sensor networks 2

7/31/2019 Wireless Sensor Networks 2

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Routing Protocols

Lecture 15

EE 493/593Wireless Sensor Networks

Outline

IP Based Routing

ID Centric Routing

Goals and Tasks

Unicast routing in MANETs

Energy efficiency & unicast routing

Multi-/broadcast routing

Geographical routing


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2

Delivery of an IP datagram

Ethernet

Token

Ring

LANEthernet

H1

R1 R2

R3 R4

H2

Network of

Ethernetswitches

Point-to-point link Point-to-point link

IP

View at the data link layer layer: Internetwork is a collection of LANs or point-to-point links or switched

networks that are connected by routers

H1

R1 R2

R3 R4

H2

10.2.1.0/24

20.1.0.0/1610.1.2.0/24

10.1.0.0/24 10.3.0.0/16

20.2.1.0/28

Delivery of an IP datagram

IP

View at the IP layer: An IP network is a logical entity with a network number

We represent an IP network as a cloud

The IP delivery service takes the view of clouds, and ignores the data linklayer view


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Tenets of End-to-End Delivery

of DatagramsThe following conditions must hold so that an IP datagram can be

successfully delivered

1. The network prefix of an IP destination address must correspond to aunique data link layer network (=LAN or point-to-point link orswitched network).(The reverse need not be true!)

2. Routers and hosts that have a common network prefix must be ableto exchange IP dagrams using a data link protocol (e.g., Ethernet,PPP)

3. Every data link layer network must be connected to at least one otherdata link layer network via a router.

1. The network prefix of an IP destination address must correspond to aunique data link layer network (=LAN or point-to-point link orswitched network).(The reverse need not be true!)

2. Routers and hosts that have a common network prefix must be ableto exchange IP dagrams using a data link protocol (e.g., Ethernet,PPP)

3. Every data link layer network must be connected to at least one otherdata link layer network via a router.

Routing tables Each router and each host keeps a rout ing table which tells the router how to

process an outgoing packet

Main columns:1. Destination address: where is the IP datagram going to?

2. Next hop: how to send the IP datagram?

3. Interface: what is the output port?

Next hop and interface column can often be summarized as one column

Routing tables are set so that datagrams gets closer to the its destination

direct

direct

R4

direct

R4

R4

Next

Hop

eth0

eth0

serial0

eth1

eth0

eth0

interface

10.1.0.0/24

10.1.2.0/24

10.2.1.0/24

10.3.1.0/24

20.1.0.0/16

20.2.1.0/28

Destination

Routing table of a host or router

IP datagrams can be directly delivered

(direct) or is sent to a router (R4)


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Delivery with Routing Tables

Destination Next Hop

10.1.0.0/2410.1.2.0/24

10.2.1.0/24

10.3.1.0/2420.1.0.0/16

20.2.1.0/28

directR3

R3

R3R3

R3

H1

R1 R2

R3 R4

H2

10.2.1.0/24

20.1.0.0/1610.1.2.0/24

10.1.0.0/24 10.3.1.0/16

20.2.1.0/28

20.2.1.2/28


10.1.0.0/2410.1.2.0/24

10.2.1.0/2410.3.1.0/24

20.1.0.0/1620.2.1.0/28

directdirect

R4direct

R4R4


10.1.0.0/2410.1.2.0/24

10.2.1.0/2410.3.1.0/24

20.1.0.0/1620.2.1.0/28

R3R3

R2direct

directR2


10.1.0.0/24

10.1.2.0/2410.2.1.0/24

10.3.1.0/24

20.2.0.0/1630.1.1.0/28

R3

directdirect

R3

R2R2


10.1.0.0/2410.1.2.0/24

10.2.1.0/2410.3.1.0/2420.1.0.0/16

20.2.1.0/28

R1R1

directR4direct

direct


10.1.0.0/2410.1.2.0/24

10.2.1.0/2410.3.1.0/2420.1.0.0/16

20.2.1.0/28

R2R2

R2R2R2

direct

to:

20.2.1.2

Delivery of IP datagrams

There are two distinct processes to delivering IPdatagrams:

1. Forwarding: How to pass a packet from an inputinterface to the output interface?

2. Routing: How to find and setup the routing tables?

Forwarding must be done as fast as possible:

on routers, is often done with support of hardware

on PCs, is done in kernel of the operating system

Routing is less time-critical

On a PC, routing is done as a background process


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Processing of an IP datagram

in IPUDP TCP

Input

queue

Lookup nexthop

Routing

Protocol

Destinationaddress local?

Static

routing

Yes

Send

datagram

IP f orwardingenabled?

No

Discard

Yes No

Demultiplex

routingtable

IP module

Data Link Layer

IP router: IP forwarding enabled

Host: IP forwarding disabled

Processing of an IP Datagramin IP

Processing of IP datagrams is very similar on an IP routerand a host

Main difference: I P forw arding is enabled on router and disabledon host

I P forw arding enabled if a datagram is received, but it is not for the localsystem, the datagram will be sent to a different system

I P forw arding disabled if a datagram is received, but it is not for the localsystem, the datagram will be dropped


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Processing of an IP datagram

at a router

1. IP header validation

2. Process options in IP header

3. Parsing the destination IP address

4. Routing table lookup

5. Decrement TTL

6. Perform fragmentation (if necessary)

7. Calculate checksum

8. Transmit to next hop

9. Send ICMP packet (if necessary)

Receive an

IP datagram

Routing Table Lookup

When a router or host needto transmit an IP datagram,it performs a routing tablelookup

Routing table lookup: Usethe IP destination address asa key to search the routingtable.

Result of the lookup is the IPaddress of a next hop router,and/or the name of anetwork interface

IP address of

next hop

router

or

Name of anetwork

interface

network prefix

or

host IP address

or

loopback

address

or

default route

Next hop/

interface

Destination

address


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Type of routing table entries Netw ork route

Destination addresses is a network address (e.g., 10.0.2.0/24) Most entries are network routes

Host route Destination address is an interface address (e.g., 10.0.1.2/32) Used to specify a separate route for certain hosts

Default r oute Used when no network or host route matches The router that is listed as the next hop of the default route is the

default gateway ( for Cisco: gateway of last resort) Loopback address

Routing table for the loopback address (127.0.0.1) The next hop lists the loopback (lo0) interface as outgoing

interface

Destination address Next hop

10.0.0.0/8

128.143.0.0/16

128.143.64.0/20

128.143.192.0/20

128.143.71.0/24

128.143.71.55/32

default

R1

R2

R3

R3

R4

R3

R5

Routing table lookup: LongestPrefix Match Longest Prefix Match: Search for

the routing table entry that has thelongest match with the prefix of thedestination IP address

1. Search for a match on all 32 bits2. Search for a match for 31 bits

..32. Search for a mach on 0 bits

Host route, loopback entry 32-bit prefix match

Default route is represented as 0.0.0.0/0 0-bit prefix match

128.143.71.21

The longest prefix match for

128.143.71.21 is for 24 bits

with entry 128.143.71.0/24

Datagram will be sent to R4


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10.1.0.0/24

R2


10.1.0.0/24

R1

Ethernet

H1

R1 R2

Routing table manipulations

with ICMP When a router detects that an IP datagram should have gone to a

different router, the router (here R2) forwards the IP datagram to the correct router

sends an ICMP redirect message to the host

Host uses ICMP message to update its routing table

(1) IP datagram

R1

(2) IP datagram(3) ICMP redirect

ICMP Router SolicitationICMP Router Advertisement

After bootstrapping a hostbroadcasts an I CMP rout ersolicitation .

In response, routers send anI CMP rout er advertisementmessage

Also, routers periodically broadcastI CMP rout er advertisement

This is sometimes called theRouter Discovery Protocol

Ethernet

H1

R1 R2

ICMP routeradvertisement

ICMP routeradvertisemen

ICMP routersolicitation


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Goals and Tasks

In any network of diameter > 1, the routing &forwarding problem appears

Constructing routing tables in ad hoc/sensornetworks

Specifically, when nodes are mobile

Specifically, for broadcast/multicast requirements

Specifically, with energy efficiency as an optimization metric

Specifically, when node position is available

Unicast, ID-centric Routing

Given: a network/a graph Each node has a unique identifier (ID)

Goal: Derive a mechanism that allows a packet sent froman arbitrary node to arrive at some arbitrary destinationnode The routing & forwarding problem

Routing: Construct data structures (e.g., tables) that containinformation how a given destination can be reached

Forwarding: Consult these data structures to forward a givenpacket to its next hop

Challenges Nodes may move around, neighborhood relations change

Optimization metrics may be more complicated than smallest hopcount e.g., energy efficiency


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Ad-hoc Routing Protocols

Because of challenges, standard routing approaches notreally applicable

Too big an overhead, too slow in reacting to changes

Examples: Dijkstras link state algorithm; Bellman-Ford distancevector algorithm

Simple solution: Flooding

Does not need any information (routing tables) simple

Packets are usually delivered to destination

But: overhead is prohibitive, usually not acceptable, either

Need specific, ad hoc rout ing protocols

Ad Hoc Routing Protocols Classification

Main question to ask: Whendoes the routing protocoloperate?

Option 1: Routing protocol alwaystries to keep its routingdata up-to-date

Protocol ispr oact ive(active before tables are actually needed) ortable-driven

Option 2: Route is only determined when actually needed

Protocol operates on demand

Option 3: Combine these behaviors

Hybridprotocols


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Ad Hoc Routing Protocols

Classification

Is the network regarded as flat or hierarchical? Compare topology control, traditional routing

Which data is used to identify nodes? An arbitrary identifier?

Theposit ionof a node? Can be used to assist in geographicrouting protocols

because choice of next hop neighbor can be computed basedon destination address

Identifiers that are not arbitrary, but carry somestructure? As in traditional routing

Structure akin to position, on a logical level?

Proactive Protocols

Idea: Start from a +/- standard routing protocol, adapt it

Adapted distance vector: Destinat ion SequenceDistance Vector (DSDV)

Based on distributed Bellman Ford procedure

Add aginginformation to route information propagated bydistance vector exchanges; helps to avoid routing loops

Periodically send full route updates

On topology change, send incremental route updates Unstable route updates are delayed

+ some smaller changes


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Proactive Protocols OLSR Combine link-state protocol & topology control

Opt imized Link Stat e Rout ing(OLSR)

Topology control component: Each node selects a minimaldominating set for its two-hop neighborhood Called the multi point relays

Only these nodes are used for packet forwarding

Allows for efficient flooding

Link-state component: Essentially a standard link-state

algorithms on this reduced topology Observation: Key idea is to reduce flooding overhead (here by

modifying topology)

Proactive Protocols CombineLS & DS: Fish Eye

Fisheye State Routing (FSR) makes basic observation:When destination is far away, details about path are notrelevant only in vicinity are details required

Look at the graph as if through a fisheye lens

Regions of different accuracy of routing information

Practically:

Each node maintains topology table of network (as in LS) Unlike LS: only distribute link state updates locally

More frequent routing updates for nodes with smaller scope


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Reactive Protocols DSR In a reactive protocol, how to forward a packet to destination?

Initially, no information about next hop is available at all

One (only?) possible recourse: Send packet to al lneighbors flood thenetwork

Hope: At some point, packet will reach destination and an answer is sentpack use this answer for backward learningthe route fromdestination to source

Practically: Dynam ic Source Routing ( DSR)

Use separate route request/ route replypackets to discover route Data packets only sent once route has been established

Discovery packets smaller than data packets

Store routing information in the discovery packets

DSR Route DiscoveryProcedure

Search for route from 1 to 5

1

7

6

5

34

2[1]

[1]

1

7

6

5

34

2

[1,7]

[1,7]

[1,4]

[1,7]

1

7

6

5

34

2[1,7,2]

[1,4,6]

[1,7,2]

[1,7,3]

1

7

6

534

2

Node 5 uses route information recorded in RREQ

to send back, via source routing, a route reply

[5,3,7,1]


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DSR Modifications, Extensions Intermediate nodes may send route replies in case they already

know a route Problem: stale route caches

Promiscuous operation of radio devices nodes can learn abouttopology by listening to control messages

Random delays for generating route replies Many nodes might know an answer reply storms

NOT necessary for medium access MAC should take care of it

Salvaging/local repair When an error is detected, usually sender times out and constructs

entire route anew

Instead: try to locally change the source-designated route

Cache management mechanisms To remove stale cache entries quickly

Fixed or adaptive lifetime, cache removal messages,

Reactive Protocols AODV

Ad hoc On Demand Distance Vectorrouting (AODV) Very popular routing protocol

Essentially same basic idea as DSR for discoveryprocedure

Nodes maintain routing tables instead of sourcerouting

Sequence numbers added to handle stale caches Nodes remember from where a packet came and

populate routing tables with that information


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Reactive Protocols TORA Observation: In hilly terrain, routing to a rivers mouth is

easy just go downhill

Idea: Turn network into hilly terrain Different landscape for each destination

Assign heights to nodes such that when going downhill,destination is reached in effect: orient edges between neighbors

Necessary: resulting directed graph has to be cycle free

Reaction to topology changes

When link is removed that was the last outlet of a node, reversedirection of all its other links (increase height!)

Reapply continuously, until each node except destination has atleast a single outlet will succeed in a connected graph!

Alternative Approach:Gossiping/Rumor Routing

Turn routing problem around: Think of an agentwandering through the network, looking for data (events, )

?

Agent initially performrandom walk

Leave traces in thenetwork

Later agents can usethese traces to find data

Essentially: works due tohigh probability of lineintersections


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Energy-efficient unicast: Goals Particularly interesting performance metric: Energy efficiency

C1

4A

2G

3D

4H

4

F

2

E

2B

1

1

1

2

2

2

2

2

3

3

Goals

Minimize energy/bit

Example: A-B-E-H

Maximize network lifetime

Time until first nodefailure, loss of coverage,partitioning

Seems trivial use proper

link/path metrics (not hopcount) and standard routing

Example: Send data from node A to node H

Basic Options for Path Metrics Maximum total available

battery capacity Path metric: Sum of battery

levels Example: A-C-F-H

Minimum battery cost routing Path metric: Sum of reciprocal

battery levels Example: A-D-H

Conditional max-min batterycapacity routing Only take battery level into

account when below a givenlevel

Minimize variance in powerlevels

Minimum total transmissionpower

C1

4A

2G

3D

4H

4F2

E

2B

1

1

1

2

2

2

2

2

3

3


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A Non-Trivial Path Metric Previous path metrics do not perform particularly well

One non-trivial link weight: wij weight for link node i to node j

eij required energy, some constant, i fraction of battery of node ialready used up

Path metric: Sum of link weights Use path with smallest metric

Properties: Many messages can be send, high network

lifetime With admission control, even a competitive ratio logarithmic in

network size can be shown

Multipath Unicast Routing

Instead of only a single path, it can be useful to computemultiple paths between a given source/destination pair

Source Sink

Disjoint paths

Primary path

Secondary path

Source Sink

Disjoint paths

Primary path

Secondary path

Source Sink

Braided paths

Primary pathSource Sink

Braided paths

Primary path

Multiple pathscan bedisjointorbraided

Usedsimultaneousl

y,alternatively,randomly,


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Broadcast & Multicast (energy-

efficient) Distribute a packet to all reachable nodes (broadcast) or to

a somehow (explicitly) denoted subgroup (multicast)

Basic options Source-based tree: Construct a tree (one for each source) to reach

all addressees

Minimize total cost (= sum of link weights) of the tree

Minimize maximum cost to each destination

Shared, core-based trees

Use only a single tree for all sources

Every source sends packets to the tree where they are distributed Mesh

Trees are only 1-connected ! use meshes to provide higher redundancyand thus robustness in mobile environments

Optimization Goals for Source-Based Trees

For each source, minimizet ot al cost This is the Steiner tree problem

again

For each source, minimizemaximu m costto eachdestination This is obtained by overlapping

the individualshortest paths ascomputed by a normal routingprotocol

Steiner tree

Source

Destination 1

Destination 2

2

2

1

Source

Destination 1

Destination 2

2

2

1

Shortest path tree


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Summary of Options

(broadcast/multicast)

Broadcast Multicast

MeshShared tree

(core-based tree)

Single

core

Multiple

core

One tree

per source

Minimizetotal cost

(Steiner tree)

Minimizecost to each node

(e.g., Dijkstra)

Wireless Multicast Advantage

Broad-/Multicasting in wireless is unlike broad-/multicasting in a wired medium Wires: locally distributing a packet to n neighbors: n times the

cost of a unicast packet

Wireless: sending to n neighbors can incur costs As high as sending to a single neighbor if receive costs are

neglected completely

As high as sending once, receiving n times if receives are tuned tothe right moment

As high as sending n unicast packets if the MAC protocol does notsupport local multicast

If local multicast is cheaper than repeated unicasts, thenw ireless mult icast advantageis present Can be assumed realistically


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Steiner Tree Approximations Computing Steiner tree is NP complete

A simple approximation

Pick some arbitrary order of all destination nodes + source node

Successively add these nodes to the tree: For every next node, constructa shortest path to some other node already on the tree

Performs reasonably well in practice

Takahashi Matsuyama heuristic Similar, but let algorithm decide which is the next node to be added

Start with source node, add that destination node to the tree which hasshortest path

Iterate, picking that destination node which has the shortest path tosome node already on the tree

Problem: Wireless multicast advantage not exploited! And does not really fit to the Steiner tree formulation

Broadcast Incremental Power(BIP)

How to broadcast, using the wireless multicast advantage?

Goal: use as little transmission power as possible

Idea: Use a minimum-spanning-tree-type construction(Prims algorithm)

But: Once a node transmits at a given power level &reaches some neighbors, it becomes cheaperto reachadditionalneighbors

From BIP to multicast incremental power (MIP): Start with broadcast tree construction, then prune unnecessary

edges out of the tree


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BIP Algorithm

BIP Example

S (3)

A

B

C (1)D

2 3

67

Round 4:

S (5)

A

B

C (1)D

3

710

Round 5:

S

A

B

CD

1

5 3

73

1

10

Round 1:

S (1)

A

B

CD

4 3

72

1

9

Round 2:

S (3)

A

B

CD

2 3

7

1

7

Round 3:


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Example for Mesh-based

Multicast Two-tier data dissemination

Overlay a mesh, route along mesh intersections

Broadcast within the quadrant where the destination is(assumed to be) located

Event

Sink

Geographic Routing

Routing tables contain information to which next hop apacket should be forwarded Explicitly constructed

Alternative: Implicitly inferthis information from physicalplacement of nodes Position of current node, current neighbors, destination known

send to a neighbor in the right direction as next hop

Geographic routi ng

Options Send to any node in a given area geocasting

Use position information to aid in routing posi t ion -basedrout ing

Might need a location serviceto map node ID to node position


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Basics of Position-based

Routing Most forward within range r strategy

Send to that neighbor that realizes the most forward progresstowards destination

NOT: farthest awayfrom sender!

Nearest node with (any) forward progress Idea: Minimize transmission power

Directional routing Choose next hop that is angularly closest to destination

Choose next hop that is closest to the connecting line todestination

Problem: Might result in loops!

Problem: Dead ends

Simple strategies might send a packet into a dead end


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Right Hand Rule to Leave

Dead Ends GPSR Basic idea to get out of a dead end: Put right hand to the wall,

follow the wall

Does not work if on some inner wall will walk in circles

Need some additional rules to detect such circles

Geometri c Perimet er Stat e Rout ing(GPSR) Earlier versions: Compass Routing II, face-2 routing

Use greedy, most forward routing as long as possible

If no progress possible: Switch to face routing Face: largest possible region of the plane that is not cut by any edge of the

graph; can be exterior or interior

Send packet around the face using right-hand rule Use position where face was entered and destination position to determine

when face can be left again, switch back to greedy routing

Requires: planar graph! (topology control can ensure that)

GPSR Example

Route packet from node A to node Z

AZ

D

C

B

E

F

G

I

H

J

K

L

Enter

face

routing

Leave facerouting


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Geographic Routing Without

Positions GEM Apparent contradiction: geographic, but no position?

Construct virtual coordinatesthat preserve enough neighborhoodinformation to be useful in geographic routing but do not require actualposition determination

Use polar coordinates froma center point

Assign virtual anglerange to neighbors of anode, bigger radius

Angles are recursivelyredistributed to childrennodes

GeRaF

How to combine position knowledge with nodes turningon/off? Goal: Transmit message over multiple hops to destination node;

deal with topology constantly changing because of on/off node

Idea: Receiver-initiatedforwarding Forwarding node S simply broadcasts a packet, without specifying

next hop node

Some node T will pick it up (ideally, closest to the source) and

forward it Problem: How to deal with multiple forwarders?

Position-informed randomization: The closer to the destination aforwarding node is, the shorter does it hesitate to forward packet

Use several annuli to make problem easier, group nodes accordingto distance (collisions can still occur)


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GeRaF Example

1 D-1

D

A1

A2

A3

A4

Location-based Multicast(LBM)

Geocasting by geographically restricted flooding

Define a forwarding zone nodes in this zone willforward the packet to make it reach the destination zone Forwarding zone specified in packet or recomputed along the way

Static zone smallest rectangle containing original sourceanddestination zone

Adaptive zone smallest rectangle containing forwarding nodeanddestination zone

Possible dead ends again Adaptive distances packet is forwarded by node u if node u is

closer to destination zones center than predecessor node v(packet has made progress)

Packet is always forwarded by nodes within the destinationzone itself


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Determining Next Hops Based

on Voronoi Diagrams Goal: Use that neighbor to forward packet that is closest to destination

among all the neighbors

Use Voronoi diagram computed for the set of neighbors of the node

currently holding the packet

S

A

B

C

D

Geocasting Using Ad hocRouting GeoTORA

Recall TORA protocol: Nodes compute a DAG withdestination as the only sink

Observation: Forwarding along the DAG still works ifmultiple nodes are destination (graph has multiple sinks)

GeoTORA: All nodes in the destination region act as sinks Forwarding along DAG; all sinks also locally broadcast the packet

in the destination region

Remark: This also works for anycasting where destinationnodes need not necessarily be neighbors Packet is then delivered to some (not even necessarily closest)

member of the group


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Mobile Nodes, Mobile Sinks

Mobile nodescause someadditionalproblems

E.g., multicast treeto distributereadings has to be

adapted

Source

Source

Source

Sink moves

downward

Sink

movesupward

SourceSource

SourceSource

SourceSource

Sink moves

downward

Sink

movesupward

Conclusion

Routing exploit various sources of information to finddestination of a packet

Explicitly constructed routing tables

Implicit topology/neighborhood information via positions

Routing can make some difference for network lifetime

However, in some scenarios (streaming data to a single sink), thereis only so much that can be done

Energy efficiency does not equal lifetime, holds for routing as well Non-standard routing tasks (multicasting, geocasting)

require adapted protocols

wireless sensor networks 2

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