Wireless Networking 1 Mobile Ad-hoc Networks (MANET) Ad-hoc network: A collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. Significant differences to existing wired networks: Wireless Self-starting No administrator Cannot assume that every computer is within communication range of every other computer Possibly quite dynamic topology of interconnections Traffic types: unicast/multicast/anycast/geocast
Mobile Ad-hoc Networks (MANET). Ad-hoc network: A collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. Significant differences to existing wired networks: Wireless Self-starting No administrator - PowerPoint PPT Presentation
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Wireless Networking 1
Mobile Ad-hoc Networks (MANET)
Ad-hoc network: A collection of wireless mobile hosts forming a
temporary network without the aid of any established infrastructure or centralized administration.
Significant differences to existing wired networks: Wireless Self-starting No administrator Cannot assume that every computer is within
communication range of every other computer Possibly quite dynamic topology of interconnections
Traffic types: unicast/multicast/anycast/geocast
Wireless Networking 2
Routing in MANET
Routing assumptions for unicast traffic Flat topology assumption
Proactive: DSDV, TORA, WRPReactive: AODV, DSR, STAR
AODV is based on the DSDV (Destination-Sequenced Distance Vector) algorithm Distance vector Different sequence numbers for each destination.
Creation of routes on a demand basis – traffic reactive Nodes that are not on a selected path do not maintain
routing information or participate in routing table exchanges!
Goal: Minimize broadcast overhead and transmission latency
Wireless Networking 29
Route Sequence Numbers
Unique counter for each destination Symbolizes the “freshness” of a route Source specifies the most recently known route
during route establishment Updated occasionally
Link failure Destination moves Intermediate nodes move
Wireless Networking 30
Route Requests from S to D in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y
Represents a node that has received RREQ for D from S
M
N
L
Wireless Networking 31
Route Requests from S to D in AODV
B
A
S E
F
H
J
D
C
G
IK
Represents transmission of RREQ
Z
YBroadcast transmission
M
N
L
Wireless Networking 32
Route Requests from S to D in AODV
B
A
S E
F
H
J
D
C
G
IK
Represents links on Reverse Path
Z
Y
M
N
L
Wireless Networking 33
Reverse Path Setup from S to D in AODV
B
A
S E
F
H
J
D
C
G
IK
• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once
Z
Y
M
N
L
Wireless Networking 34
Reverse Path Setup from S to D in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y
M
N
L
Wireless Networking 35
Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y• Node D does not forward RREQ, because node D is the intended target of the RREQ
M
N
L
Wireless Networking 36
Route Reply from D to S in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y
Represents links on path taken by RREP
M
N
L
Wireless Networking 37
Route Reply in AODV
Intermediate node may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender S Recent path means higher sequence number
The likelihood that an intermediate node will send a RREP not as high as DSR An intermediate node which knows a route, but with a
smaller sequence number, cannot send Route Reply
Wireless Networking 38
Forward Path Setup in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y
M
N
L
Forward links are setup when RREP travels alongthe reverse path
Represents a link on the forward path
Wireless Networking 39
Data Delivery in AODV
B
A
S E
F
H
J
D
C
G
IK
Z
Y
M
N
L
Routing table entries used to forward data packet.Route is not included in packet header.
DATA
Wireless Networking 40
Local Link Maintenance
Periodic “hello” messages broadcast to immediate neighbors Failing to receive hello messages indicates a link failure
Link failure notifications sent to source nodes Sources rediscover new route to destination
Wireless Networking 41
AODV Key Advantages
“Partial” routing tables are constructed reactively Entries are updated only when a node sends to an unreachable node No periodic global updates Node not on active paths maintain no routing entries Reduce packet overhead
Routing table No source routing needed reduce bit overhead “Route caching” reduce establishment latency Sequence number override stale routes source based broadcast id loop freedom
Push link failure to relevant nodes Reduce establishment latency
Wireless Networking 42
AODV and DSR : Disadvantages
Common problems for both AODV and DSR Potential 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 Random delays + carrier sensing