Routing Protocols in MANET's by Ashok Panwar

Presented By:-
Ashok Panwar
Technical Officer in ECIL(NPCIL)
Tarapur, Mumbai
Routing Protocols
in MANETs
1

What is a MANET
Mobile nodes, wireless links
Infrastructure-less: by the nodes, …
Multi-hop routing: …, and for the nodes
Minimal administration: no hassles
2
Ashok Panwar
Technical Officer in ECIL

What’s unique about a MANET ?
Moving nodes  ever changing topology
Wireless links
  various and volatile link quality
Pervasive (cheap) devices
 Power constraints
Security
 Confidentiality, other attacks
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Ashok Panwar

Challenges in MANET Routing
Need dynamic routing
Frequent topological changes possible.
Very different from dynamic routing in the Internet.
Potential of network partitions.
Routing overhead must be kept minimal
Wireless  low bandwidth
Mobile  low power
Minimize # of routing control messages
Minimize routing state at each node
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Ashok Panwar

Other Challenges
Auto configuration issues
Address assignment
Service discovery
Security issues
Ease of denial-of-service attack
Misbehaving nodes difficult to identify
Nodes can be easily compromised
New Applications/services
Location based: Distribute some information to all nodes in a
geographic area (geocast).
Content based: Query all sensors that sensed something particular in
the past hour.
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Ashok Panwar

MANET Protocol Zoo
Topology based routing
 Proactive approach, e.g., DSDV.
 Reactive approach, e.g., DSR, AODV, TORA.
 Hybrid approach, e.g., Cluster, ZRP.
 Position based routing
 Location Services:
DREAM, Quorum-based, GLS, Home zone etc.
 Forwarding Strategy:
Greedy, GPSR, RDF, Hierarchical, etc.
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Ashok Panwar

Routing Protocols
Reactive (On-demand) protocols
Discover routes when needed
Source-initiated route discovery
Proactive protocols
Traditional distributed shortest-path protocols
Based on periodic updates. High routing overhead
Tradeoff
State maintenance traffic vs. route discovery traffic
Route via maintained route vs. delay for route discovery
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Ashok Panwar

Reactive Routing
Key Goal: Reduction in routing overhead
Useful when number of traffic sessions is much lower
than the number of nodes.
No routing structure created a priori. Let the
structure emerge in response to a need
Two key methods for route discovery
source routing
backward learning (similar to intra-AS routing)
Introduces delay
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Ashok Panwar

Reactive (on-demand) routing:
Routing only when needed
0
5
1
2
4
3
query(0)
query(0)
query(0)
query(0)
query(0)
query(0)
query(0)
reply(0)
reply(0)
reply(0)
Advantages:
 eliminate periodic updates
 adaptive to network dynamics
Disadvantages:
 high flood-search overhead with
mobility, distributed traffic
 high route acquisition latency
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Ashok Panwar

Reactive Routing – Source initiated
Source floods the network with a route request packet
when a route is required to a destination
Flood is propagated outwards from the source
Pure flooding = every node transmits the request only once
Destination replies to request
Reply uses reversed path of route request
sets up the forward path
Two key protocols: DSR and AODV
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Ashok Panwar

Dynamic Source Routing (DSR)
Cooperative nodes
Relatively small network diameter (5-10 hops)
Detectable packet error
Unidirectional or bidirectional link
Promiscuous mode (optional)
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Ashok Panwar

A
B
C
E
D
G
H
F
A
A
A-B
A-C
A-C-E
A-C-E
A-C-E
A-B-D
A-B-D-G
A-B-D-G
A-B-D-G
Route Discovery
A-B-C
A-B-C
Route Request (RREQ)
Route Reply (RREP)
Route Discovery is issued with exponential back-off intervals.Route Discovery is issued with exponential back-off intervals.
Initiator ID
Initiator seq#
Target ID
Partial route
RREQ FORMATRREQ FORMAT
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Ashok Panwar

Route Discovery: at source A
A need to send to G
Lookup Cache for route A to G
Route
found?
Start Route
Discovery
Protocol
Continue
normal
processing
Route Discovery
finished
Packet in
buffer?
Send packet to
next-hop
done
Buffer
packet
no
Write route in
packet header
yes
yes
no
wait
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Ashok Panwar

Route Discovery: At an intermediate node
Accept route
request packet
<src,id> in
recently seen
requests list?
Discard
route
request
yes
no
Host’s address
already in patrial
route
Discard
route
request
yes
Store <src,id> in list
Broadcast packet
Send route reply
packet
done
myAddr=t
arget
no
Append myAddr to
partial route no
yes
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Ashok Panwar

DSR - Route Discovery
Route ReplyRoute Reply message containing path information is sent
back to the source either by
the destination, or
intermediate nodes that have a route to the destination
Reverse the order of the route record, and include it in Route
Reply.
Unicast, source routing
Each node maintains a Route CacheRoute Cache which records routes it
has learned and overheard over time
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Ashok Panwar

Route Maintenance
Route maintenance performed only while route is in use
Error detection:
Monitors the validity of existing routes by passively listening to
data packets transmitted at neighboring nodes
Lower level acknowledgements
When problem detected, send Route ErrorRoute Error packet to
original sender to perform new route discovery
Host detects the error and the host it was attempting;
Route ErrorRoute Error is sent back to the sender the packet – original srcis sent back to the sender the packet – original src
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Ashok Panwar

A
B
C
E
D
G
H
F
G
RERR
RERR
Route Cache (A)
G: A, B, D, G G: A,
C, E, H, G
F: B, C, F
Route Maintenance
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Ashok Panwar

A Summary of DSRA Summary of DSR
Entirely on-demand, potentially zero control message overhead
Trivially loop-free with source routing
Conceptually supports unidirectional links as well as
bidirectional links
High packet delays/jitters associated with on-demand routing
Space overhead in packets and route caches
Promiscuous mode operations consume excessive amount of
power
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Ashok Panwar

Break…
Then AODV
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Ashok Panwar

AODV Routing Protocol
AODV = Ad Hoc On-demand Distance Vector
Source floods route request in the network.
Reverse paths are formed when a node hears a route request.
Each node forwards the request only once (pure flooding).
A
S E
F
B
C
G D
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Ashok Panwar

AODV Route Discovery
Source floods route request in the network.
A
S E
F
B
C
G D
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Ashok Panwar

Uses hop-by-hop routing.
Reverse paths are formed when a node hears a route request.
A
S E
F
B
C
G D
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Ashok Panwar

Route reply forwarded via the reverse path.
A
S E
F
B
C
G D
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Ashok Panwar

Route reply is forwarded via the reverse path …
thus forming the forward path.
The forward path is used to route data packets.
A
S E
F
B
C
G D
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Ashok Panwar

Route Expiry
Unused paths expire based on a timer.
A
S E
F
B
C
G D
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Ashok Panwar

AODV – Optimization
Useful optimization: An intermediate node with a
route to D can reply to route request.
Faster operation.
Quenches route request flood.
Above optimization can cause loops in presence of
link failures
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Ashok Panwar

AODV: Routing Loops
Assume, link C-D fails, and node A does not know about it
(route error packet from C is lost).
C performs a route discovery for D.
Node A receives the route request (via path C-E-A)
Node A replies, since A knows a route to D via node B
Results in a loop: C-E-A-B-C
A B C D
E
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Ashok Panwar

AODV: Routing Loops
A B C D
E
• Assume, the link C-D fails, and node A does not know about
it (route error packet from C is lost).
• C performs a route discovery for D.
• Node A receives the route request (via path C-E-A)
• Node A replies, since A knows a route to D via node B
• Results in a loop: C-E-A-B-C
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Ashok Panwar

AODV: Use Sequence Numbers
Each node X maintains a sequence number
acts as a time stamp
incremented every time X sends any message)
Each route to X (at any node Y) also has X’s
sequence number associated with it, which is Y’s
latest knowledge of X’s sequence number.
Sequence number signifies ‘freshness’ of the route
– higher the number, more up to date is the route.
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Ashok Panwar

Use of Sequence Numbers in AODV
Loop freedom: Intermediate node replies with a route
(instead of forwarding request) only if it has a route
with a higher associated sequence number.
S Y D?
Dest seq. no. = 10 Has a route to D
with seq. no = 7 Seq. no. = 15
RREQ carries 10 Y does not reply, but
forwards the RREQ
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Ashok Panwar

Avoidance of Loop
Link failure increments the DSN at C (now is 10).
If C needs route to D, RREQ carries the DSN (10).
A does not reply as its own DSN is less than 10.
A B C D
E
109
9
7
5
All DNS’s are for D
DSN = Destination Sequence Number.
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Ashok Panwar

Path Maintenance
Movement not along active path triggers no action
If source moves, reinitiate route discovery
When destination or intermediate node moves
 upstream node of break broadcasts Route Error (RERR)
 RERR contains list of all destinations no longer reachable due to link
break
 RERR propagated until node with no precursors for destination is
reached
Source
Destination
1
2
3
4
3’
Source
Destination
1
2
4
3’
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Ashok Panwar

Summary: AODV
At most one route per destination maintained at
each node
After link break, all routes using the failed link are erased.
Expiration based on timeouts.
Use of sequence numbers to prevent loops.
Optimizations
 Routing tables instead of storing full routes.
 Control flooding (incrementally increase ‘region’)
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Ashok Panwar

Other notes
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Ashok Panwar

Proposed Routing Approaches
Conventional wired-type schemes (global routing,
proactive):
Distance Vector; Link State
Hierarchical (global routing) schemes:
Fisheye, Hierarchical State Routing, Landmark Routing
On- Demand, reactive routing:
Source routing; backward learning
Location Assisted routing (Geo-routing):
DREAM, LAR etc
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Ashok Panwar

Conventional wired routing limitations
Distance Vector (eg, Bellman-Ford, DSDV):
routing control O/H linearly increasing with net size
convergence problems (count to infinity); potential loops
Link State (eg, OSPF):
link update flooding O/H caused by frequent topology
changes
CONVENTIONAL ROUTING DOES NOT SCALE TO SIZE AND
MOBILITY
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Ashok Panwar

Distance Vector
0
5
1
2
4
3
Destination Next Hop Distance
0 2 3
1 2 2
… … …
Routing table at node 5 :
Tables grow linearly with # nodes
Control O/H grows with
mobility and size
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Ashok Panwar

Link State Routing
 At node 5, based on the link
state packets, topology table is
constructed:
 Dijkstra’s Algorithm can then
be used for the shortest path
0
5
1
2
4
3
{1}
{0,2,3}
{1,4}
{2,4}
{2,3,5}
{1,4,5}
0 1 2 3 4 5
0 1 1 0 0 0 0
1 1 1 1 1 0 0
2 0 1 1 0 1 1
3 0 1 0 1 1 0
4 0 0 1 1 1 1
5 0 0 1 0 1 1
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Ashok Panwar

Existing On-Demand Protocols
Dynamic Source Routing (DSR)
Associativity - Based Routing (ABR)
Ad-hoc On-demand Distance Vector (AODV)
Temporarily Ordered Routing Algorithm (TORA)
Zone Routing Protocol (ZRP)
Signal Stability Based Adaptive Routing (SSA)
On Demand Multicast Routing Protocol (ODMRP)
…
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Ashok Panwar

Routing Protocols in MANET's by Ashok Panwar

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