Post on 07-Apr-2018
lmfeeney@sics.se
Introduction to MANET Routing
Laura Marie FeeneySwedish Institute of Computer Science
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MANET
MANET: Mobile Ad hoc NETworkn mobile wireless network, capable of
autonomous operationn operates without base station
infrastructuren nodes cooperate to provide
connectivityn operates without centralized
administrationn nodes cooperate to provide services
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Ad hoc routing
infrastructureless network
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Ad hoc routing
“equivalent” topology
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Ad hoc routing
dynamic multihop routing
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Ad hoc routing
route failure due to mobility
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Ad hoc routing
dynamic route repair
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Applications
n tactical (military) networks (FOI)n disaster recovery servicesn metropolitan/campus-area
communication networks (UU)n sensor networks (SICS)n enhanced cellular networks (KTH)n delay-tolerant networking (LUTH)
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Definition
How is a MANET different from othernetworks?n Internetn WLANn MobileIP
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Internet/Intranet
default router
Internet routing(+ humans)
networkprovider
managing infrastructure requiressignificant expert configuration
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Cellular (WLAN)
mobiles communicate only withbase-stations
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MobileIP
correspondent
CN
MNhome
FA
Mobile-IP allows a node to change itspoint of attachment to the network
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MobileIPCN FA
HA
MN
mobiles register location with homeagent, which tunnels traffic
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Status
Still largely an R&D activityn IETF MANET working group
u two protocols will become“proposed standards”
n IRTF working groupn research communityn small-scale testbeds and simulation
experiments
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Overview
n ad hoc routing problemu challengesu design choicesu protocol example
n other problemsu security & cooperationu servicesu wireless issues
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Challenges
n distributed state in unreliableenvironment
n dynamic topologyn limited network capacityn wireless communication
u variable link qualityu interference and collisionsu energy-constrained nodes
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Criteria
n effectivenessu convergence/recoveryu scalability (number of nodes,
density)n performance
u data throughputu route latency (delay)u route optimality
(hops/stability/diversity)u overhead cost
(packets/bandwidth/energy)
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Alphabet Soup
many proposed protocols:AODV CEDAR ABR FSR
TORA GSR OLSR LANMAR
ZRP LAR DSR OSPF++
RDMAR CBRP DSDV WRP
TBRPF CGSR GPSR
protocols in red are best known
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Design Choicesprotocols fall into a few main categoriesn
n on-demand (reactive)n table-driven (pro-active)n flooding-basedn cluster-basedn geographicn application specific (cross-layer)
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Design Choices
no pre-assigned backbonecan designate a backbone dynamicallybackbone provides structure for thenetworkn increases (?) scalabilityn cost to maintain backbone structuren disproportionate load on backbone
nodesCEDAR is an example
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Routing backbone
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n connected backbone; each node hasa backbone neighbor
n distributed computation of aconnected minimum dominating set ishard
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Routing backbone
?
2
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1
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58 11
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97
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1412
?
n maintaining the backbone can becostly
n common strategyperiodic broadcast of neighbor data,backbone nodes self-nominate viaadaptive backoff
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Routing backbone
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n non-backbone nodes have “default”router
n how to route across the backbone??
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Reactive Routing
n reactive (on-demand) protocoln only obtain route information when
neededn advantages
u no overhead from periodic updaten disadvantages
u high route latencyu route caching can reduce latency
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Pro-active routing
n pro-active (table-driven) protocoln more similar to conventional routingn advantages
u low route latencyu state information
n disadvantagesu high overhead (periodic table
updates)u route repair depends on update
frequency
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AODV (DYMO)
Ad hoc On-demand Distance Vector(Perkins et.al.)
n conventional distance vectoru nodes exchange distance tables
with their neighborsu periodic exchange and immediate
update for changesu routing table selects shortest path
n exchange a lot of information that isnever used
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AODV Strategy
n on-demand variant of conventionaldistance vector
route request (RREQ) is floodedthrough the networkroute discovery creates (temporary)reverse routesroute reply (RREP) activatesforward route
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AODV Strategy (cont’)
n handling topology changelink failure generates route error(RERR)destination managed sequencenumber ensures loop freedom
n simplified presentation follows...
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AODV
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1
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58 11
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97
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n on-demand routing protocoln node 1→ 14
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AODV (RREQ)
14?
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n broadcast flood route requestmessageu (broadcast traffic in red)
n “wireless multicast advantage”
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AODV (RREQ)1/14: 1
14
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1/14: 1
1/14
: 12
n node from which RREQ was receiveddefines a reverse route to the sourceu (“reverse routing table entries” blue)
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AODV (RREQ)
1/14: 1
14?
14?
3 14?
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5
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8
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10
912
13
1
142
n route request is flooded through thenetwork
n reverse routing table entries (blue arrows)
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AODV (RREQ)
1/14: 1
3
1/14:5
4
5
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8
7
11
10
912
13
1
142
n unreliable communicationn destination managed sequence
number, ID prevent looping
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AODV (RREQ)
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142
n flooding is expensiven broadcast collision problem
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AODV (RREQ)
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n route request arrives at thedestination
n two routes are discovered
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AODV (RREP)
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n destination sends route reply (setsequence number)u (unicast reply in magenta)
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AODV (RREP)
14:14(n)
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3
912
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1
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n routing table now contains forwardroute to the destinationu (“reverse routing table entries” in blue)
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AODV (RREP)
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3
912
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1
142
n route reply follows reverse route backto the source
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AODV (RREP)
14:13(n)
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912
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1
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n setting the forward routing tableentries along the way
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AODV (RREP)
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4
5
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8
7
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3
912
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1
142
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AODV (RREP)
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4
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3
912
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n route reply reaches the source
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AODV (RREP)
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n source adopts destination sequencenumber
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AODV
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1
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2
n traffic flows along the forward routen forward route is refreshed, reverse
routes time out
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AODV (RERR)
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14
1
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129
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n link failure detection
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AODV (RERR)
14:10(n+1)
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1
13
129
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7
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3
n return error message to the source(increment sequence number)
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AODV (RERR)
214
1
13
129
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7
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3
n source receives route error
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AODV (RREQ)
3
14
1
13
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2
n re-initiates route discovery process
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Criteria
n effectivenessconvergence/recoveryscalability (number of nodes,density)
n performancedata throughputroute latency (delay)route optimality(hops/stability/diversity)overhead cost(packets/bandwidth/energy)
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Design Choices
n reactive (on-demand) protocolu high route latencyu no overhead from periodic updateu route caching can reduce latency
n pro-active (table-driven) protocolu low route latencyu high overhead (periodic table
updates)u route repair depends on update
frequency
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OLSR
Optimized Link State RoutingJacquet et. al.
n conventional link-state routingu beacon to determine neighborsu for each node, disseminate its links
to all other nodesu use SPF algorithm to generate
routing tablen high overhead, exchange information
for links that are never used
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OLSR Strategy
n optimized variant of conventional linkstate routing
for each node, disseminate onlysome of its linksfor each node, only disseminateinformation received via some linksuse SPF algorithm to generaterouting table
n “some (carefully selected!) links” =multipoint relay set
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2-hop Neighborhoodbroadcast periodic “hello” messages
each message contains a list ofneighborseach node discovers its 2-hopneighborhooddiscovers failed linksdiscovers bi-directional links
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Bi-directional Links
HELLO(3)={1,2,4,7}
HELLO(6)={2,3,7}
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Bi-directional Links
NBR(3)={1,2,4,7}
NBR(3)={1,2,4,7}HELLO(6)={2,3,7}
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3
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1
2
13
129
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4
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Multipoint Relay
multipoint relay set (MPR): subset of anode’s 1-hop neighbors, such that eachof its 2-hop neighbors is a 1-hopneighbor of a node in the MPR setin practice, approximate optimal MPRsetnote that each node independentlydetermines its own MPR set (no global“network MPR set”)
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Multipoint Relay
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1
one and two hop neighbors of node 4
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Multipoint Relay (MPR set)
MS(3)={4,...}
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2
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1185
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MPR(4)={3,7,8}
MS(8)={4,...}
MS(7)={4,...}
node 5 is not needed in the multipointrelay set
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Dense Network
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with greater node density, theproportion of relay nodes is smaller
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Dense Network (MPR set)
{3,8}
{4,10}
{10}
{1,4,8}
{8,10}
{4,7}{1,3}
{3,5}
{7,8,12} {9,10}
{10}{7,8}
{6,4,10}
{2,7}
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14
1
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4
8
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nodes which are not in the MPR setare somehow redundant
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Dense Network (MS set)
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multipoint selector (MS) set is theinverse of MPR set
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OLSROperation:
each node uses HELLO message tocalculate and announce its MPR seta node sends link state informationonly for nodes in its MS set (for whichit is an MPR)each node processes (SPF routes) alllink state messagesa node only rebroadcasts link statemessages from nodes in its MS set
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OLSR (Dense Network)
only disseminate link data for greennodesonly rebroadcast data from green
nodes
1: 4 2 3 5 2: 1 3 6 3: 1 2 4 6 7
4: 1 3 5 7 8 5: 1 5 8 6: 2 3 7
7: 3 4 6 9 10 8: 4 5 9 10 11 9: 7 10 12
10: 7 8 9 11 12 13 11: 8 10 13 12: 9 10 13 14
13: 10 11 12 14 14: 10 12 13