Manet By Vikas mainanwal

Mobile Ad Hoc Networks
Subject – Mobile Computing
Course – M.Tech. CSE (Networking Systems)
by
Vikash MainanwaI
Submitted to
Rajdeep Singh
Department of Computer Science & Engineering
Punjab Institute of Technology, Kapurthala
(PTU Main Campus )

Outline
 Introduction
 Medium Access Control
 Routing (unicast)
– Reactive Protocols
– Proactive Protocols
– Hybrid Protocols
 Transport Issues
 Summary and Conclusions

Wireless Networks
 Need: Access computing and communication services, on the move
 Infrastructure-based Networks
– traditional cellular systems (base station infrastructure)
 Wireless LANs
– Infrared (IrDA) or radio links (Wavelan)
– very flexible within the reception area; ad-hoc networks possible
– low bandwidth compared to wired networks (1-10 Mbit/s)
 Ad hoc Networks
– useful when infrastructure not available, impractical, or expensive
– military applications, rescue, home networking

Cellular Wireless
 Single hop wireless connectivity to the wired world
– Space divided into cells
– A base station is responsible to communicate with hosts in its cell
– Mobile hosts can change cells while communicating
– Hand-off occurs when a mobile host starts communicating via a
new base station

Multi-Hop Wireless
 May need to traverse multiple links to reach destination
 Mobility causes route changes

Mobile Ad Hoc Networks (MANET)
 Host movement frequent
 Topology change frequent
 No cellular infrastructure. Multi-hop wireless links.
 Data must be routed via intermediate nodes.
A
B A
B

Why Ad Hoc Networks ?
 Setting up of fixed access points and backbone
infrastructure is not always viable
– Infrastructure may not be present in a disaster area or war zone
– Infrastructure may not be practical for short-range radios;
Bluetooth (range ~ 10m)
 Ad hoc networks:
– Do not need backbone infrastructure support
– Are easy to deploy
– Useful when infrastructure is absent, destroyed or impractical

Traditional Routing
 A routing protocol sets up a routing table in routers
 A node makes a local choice depending on global
topology

Distance-vector & Link-state Routing
 Both assume router knows
– address of each neighbor
– cost of reaching each neighbor
 Both allow a router to determine global routing
information by talking to its neighbors
 Distance vector - router knows cost to each destination
 Link state - router knows entire network topology and
computes shortest path

Distance Vector Routing: Example


2


Routing and Mobility
 Finding a path from a source to a destination
 Issues
– Frequent route changes
• amount of data transferred between route changes may be
much smaller than traditional networks
– Route changes may be related to host movement
– Low bandwidth links
 Goal of routing protocols
– decrease routing-related overhead
– find short routes
– find “stable” routes (despite mobility)

Unicasting
 The routing we have discussed so far is mainly point-to-
point routing.
 A source node wants to send a message to a destination
node.

Multicasting
 However, in many situations a node wants to send a
message to a group of nodes in the network.
 This is called multicasting and the group is called a
multicast group.

Broadcasting
 Broadcasting is a special case of multicasting when all the
nodes in the network is in the multicast group.

Unicast Routing Protocols
 Many protocols have been proposed
 Some specifically invented for MANET
 Others adapted from protocols for wired networks
 No single protocol works well in all environments
– some attempts made to develop adaptive/hybrid protocols
 Standardization efforts in IETF
– MANET, MobileIP working groups
– http://www.ietf.org

Routing Protocols
 Proactive protocols
– Traditional distributed shortest-path protocols
– Maintain routes between every host pair at all times
– Based on periodic updates; High routing overhead
– Example: DSDV (destination sequenced distance vector)
 Reactive protocols
– Determine route if and when needed
– Source initiates route discovery
– Example: DSR (dynamic source routing)
 Hybrid protocols
– Adaptive; Combination of proactive and reactive
– Example : ZRP (zone routing protocol)

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 the traffic and
mobility patterns

Dynamic Source Routing (DSR) [Johnson96]
 When node S wants to send a packet to node D, but does
not know a route to D, node S initiates a route discovery
 Source node S floods Route Request (RREQ)
 Each node appends own identifier when forwarding RREQ

Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
Represents a node that has received RREQ for D from S
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ

B
A
S E
F
H
J
D
C
G
I
K
• Node H receives packet RREQ from two neighbors:
potential for collision
Z
Y
M
N
L
[S,E]
[S,C]

B
A
S E
F
H
J
D
C
G
I
K
• 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
[S,C,G]
[S,E,F]

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
N
L
[S,C,G,K]
[S,E,F,J]

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
• Node D does not forward RREQ, because node D
is the intended target of the route discovery
M
N
L
[S,E,F,J,M]

 Destination D on receiving the first RREQ, sends a Route
Reply (RREP)
 RREP is sent on a route obtained by reversing the route
appended to received RREQ
 RREP includes the route from S to D on which RREQ was
received by node D

Route Reply in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message

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

Data Delivery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
DATA [S,E,F,J,D]
Packet header size grows with route length

DSR Optimization: Route Caching
 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
 Problem: Stale caches may increase overheads

Dynamic Source Routing: Advantages
 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

Dynamic Source Routing: Disadvantages
 Packet header size grows with route length due to source
routing
 Flood of route requests may potentially reach all nodes in
the network
 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
 Stale caches will lead to increased overhead

Location-Aided Routing (LAR) [Ko98Mobicom]
 Exploits location information to limit scope of route
request flood
– Location information may be obtained using GPS
 Expected Zone is determined as a region that is expected to
hold the current location of the destination
– Expected region determined based on potentially old location
information, and knowledge of the destination’s speed
 Route requests limited to a Request Zone that contains the
Expected Zone and location of the sender node

Request Zone
 Define a Request Zone
 LAR is same as flooding, except that only nodes in request
zone forward route request
 Smallest rectangle including S and expected zone for D
S
Request Zone
D
Expected Zone
x
Y

Location Aided Routing (LAR)
 Advantages
– reduces the scope of route request flood
– reduces overhead of route discovery
 Disadvantages
– Nodes need to know their physical locations
– Does not take into account possible existence of obstructions for
radio transmissions

Ad Hoc On-Demand Distance Vector Routing
(AODV) [Perkins99Wmcsa]
 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

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 (RREP)
 Route Reply travels along the reverse path set-up when
Route Request is forwarded

RREQ Message
 a
B?B?
B?B?
B?B?
B?B?
B?B?
B?B? B?B?
BB
AA

RREP Message
a
BB
AA
AA
AA
AA
AA
AA
AA

Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
Represents a node that has received RREQ for D from S
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Represents links on Reverse Path
Z
Y
M
N
L

Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
• 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

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L

B
A
S E
F
H
J
D
C
G
I
K
Z
Y
• Node D does not forward RREQ, because node D
is the intended target of the RREQ
M
N
L

Forward Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
Forward links are setup when RREP travels along
the reverse path
Represents a link on the forward path

Route Request and Route Reply
 Route Request (RREQ) includes the last known sequence number for
the destination
 An intermediate node may also send a Route Reply (RREP) provided
that it knows a more recent path than the one previously known to
sender
 Intermediate nodes that forward the RREP, also record the next hop to
destination
 A routing table entry maintaining a reverse path is purged after a
timeout interval
 A routing table entry maintaining a forward path is purged if not used
for a active_route_timeout interval

Link Failure
 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
 Neighboring nodes periodically exchange hello message
 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 (RERR)
messages, which also update destination sequence numbers

Route Error
 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
 When node D receives the route request with destination sequence
number N, node D will set its sequence number to N, unless it is
already larger than N

AODV: Summary
 Routes need not be included in packet headers
 Nodes maintain routing tables containing entries only for
routes that are in active use
 At most one next-hop per destination maintained at each
node
– DSR may maintain several routes for a single destination
 Sequence numbers are used to avoid old/broken routes
 Sequence numbers prevent formation of routing loops
 Unused routes expire even if topology does not change

Other Protocols
 Many variations of using control packet flooding for route discovery
 Power-Aware Routing [Singh98Mobicom]
– Assign a weight to each link: function of energy consumed when
transmitting a packet on that link, as well as the residual energy level
– Modify DSR to incorporate weights and prefer a route with the smallest
aggregate weight
 Associativity-Based Routing (ABR) [Toh97]
– Only links that have been stable for some minimum duration are utilized
– Nodes increment the associativity ticks of neighbors by using periodic
beacons
 Signal Stability Based Adaptive Routing (SSA) [Dube97]
– A node X re-broadcasts a Route Request received from Y only if the
(X,Y) link has a strong signal stability
– Signal stability is evaluated as a moving average of the signal strength of
packets received on the link in recent past

Signal Stability Routing (SSA)

Link Reversal Algorithm [Gafni81]
A FB
C E G
D

Link Reversal Algorithm
A FB
C E G
D
Maintain a directed acyclic
graph (DAG) for each
destination, with the destination
being the only sink
This DAG is for destination
node D
Links are bi-directional
But algorithm imposes
logical directions on them

Link (G,D) broke
A FB
C E G
D
Any node, other than the destination, that has no outgoing links
reverses all its incoming links.
Node G has no outgoing links

A FB
C E G
D
Now nodes E and F have no outgoing links
Represents a
link that was
reversed recently

A FB
C E G
D
Now nodes B and G have no outgoing links
Represents a
link that was
reversed recently

A FB
C E G
D
Now nodes A and F have no outgoing links
Represents a
link that was
reversed recently

A FB
C E G
D
Now all nodes (other than destination D) have an outgoing link
Represents a
link that was
reversed recently

A FB
C E G
D
DAG has been restored with only the destination as a sink

 Attempts to keep link reversals local to where the failure
occurred
– But this is not guaranteed
 When the first packet is sent to a destination, the
destination oriented DAG is constructed
 The initial construction does result in flooding of control
packets

 The previous algorithm is called a full reversal method
since when a node reverses links, it reverses all its
incoming links
 Partial reversal method [Gafni81]: A node reverses
incoming links from only those neighbors who have not
themselves reversed links “previously”
– If all neighbors have reversed links, then the node reverses all its
incoming links
– “Previously” at node X means since the last link reversal done by
node X

Link Reversal Methods
 Advantages
– Link reversal methods attempt to limit updates to routing tables at
nodes in the vicinity of a broken link
• Partial reversal method tends to be better than full reversal
method
– Each node may potentially have multiple routes to a destination
 Disadvantages
– Need a mechanism to detect link failure
• hello messages may be used
– If network is partitioned, link reversals continue indefinitely

Temporally-Ordered Routing Algorithm
(TORA) [Park97Infocom]
 Route optimality is considered of secondary importance; longer routes
may be used
 At each node, a logically separate copy of TORA is run for each
destination, that computes the height of the node with respect to the
destination
 Height captures number of hops and next hop
 Route discovery is by using query and update packets
 TORA modifies the partial link reversal method to be able to detect
partitions
 When a partition is detected, all nodes in the partition are informed,
and link reversals in that partition cease

Asymmetric Algorithms
 Clusterhead Gateway Switch Routing (CGSR)
– All nodes within a cluster communicate with a clusterhead
– Routing uses a hierarchical clusterhead-to-gateway approach
 Core-Extraction Distributed Ad Hoc Routing (CEDAR)
[Sivakumar99]
– A subset of nodes in the network is identified as the core
– Each node in the network must be adjacent to at least one node in
the core
– Each core node determines paths to nearby core nodes by means of
a localized broadcast

CEDAR
B
A
C E
JS K
D
F
H
G
A core node
Node E is the dominator
for nodes D, F and K

Destination-Sequenced Distance-Vector (DSDV)
[Perkins94Sigcomm]
 Each node maintains a routing table which stores
– next hop, cost metric towards each destination
– a sequence number that is created by the destination itself
 Each node periodically forwards routing table to neighbors
– Each node increments and appends its sequence number when sending its
local routing table
 Each route is tagged with a sequence number; routes with greater
sequence numbers are preferred
 Each node advertises a monotonically increasing even sequence
number for itself
 When a node decides that a route is broken, it increments the sequence
number of the route and advertises it with infinite metric
 Destination advertises new sequence number

Destination-Sequenced Distance-Vector (DSDV)
 When X receives information from Y about a route to Z
– Let destination sequence number for Z at X be S(X), S(Y) is sent
from Y
– If S(X) > S(Y), then X ignores the routing information received
from Y
– If S(X) = S(Y), and cost of going through Y is smaller than the
route known to X, then X sets Y as the next hop to Z
– If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is
updated to equal S(Y)
X Y Z

Optimized Link State Routing (OLSR)
[Jacquet00ietf]
 Nodes C and E are multipoint relays of node A
– Multipoint relays of A are its neighbors such that each two-hop
neighbor of A is a one-hop neighbor of one multipoint relay of A
– Nodes exchange neighbor lists to know their 2-hop neighbors and
choose the multipoint relays
A
B F
C
D
E H
G
K
J
Node that has broadcast state information from A

Optimized Link State Routing (OLSR)
 Nodes C and E forward information received from A
 Nodes E and K are multipoint relays for node H
 Node K forwards information received from H
A
B F
C
D
E H
G
K
J
Node that has broadcast state information from A

Zone Routing Protocol (ZRP) [Haas98]
 ZRP combines proactive and reactive approaches
 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: Proactively maintain routes to all nodes
within the source node’s own zone.
 Inter-zone routing: Use an on-demand protocol (similar to
DSR or AODV) to determine routes to outside zone.

Zone Routing Protocol (ZRP)
Radius of routing zone = 2

Manet By Vikas mainanwal

More Related Content

What's hot (20)

Viewers also liked (6)

Similar to Manet By Vikas mainanwal (20)

More from VIKASH MAINANWAL (6)

Recently uploaded (6)

Manet By Vikas mainanwal