Issues: Routing in Ad-hoc
Networks
 Mobility
 Bandwidth constraint
 Error-prone and shared channel
 Location-dependent contention
 Other resource constraints
1
Issues: Multicast routing ...
 Efficient group management
 Robustness
 Efficiency
 Control overhead
 Quality of service
 Scalability
 Security
2
3
Unicast Routing Protocols
 Many protocols have been proposed
 Some have been invented specifically for
MANET
 Others are adapted from previously
proposed protocols for wired networks
 No single protocol works well in all
environments

some attempts to develop adaptive protocols
4
The ideal protocol (p303)
 Distributed
 Localized (and scalable)
 Adaptive
 Minimal maintenance and overhead
 Loop free (and free from stale routes)
 Balance scares resources usage against
performance (and/or QoS)
5
Routing protocol classification
 Route information mechanism
Proactive (table-driven)
 Reactive (demand-driven)
 Hybrid
 Temporal information
 Past vs. Future information
 Routing toplogy
 Flat vs. hierarchical
 Specific resources
 Geography or Power

6
Routing protocols for wireless ad
hoc networks
Sensor networks
Mobile ad hoc networks
Response time,
bandwidth
Proactive
protocols
Optimized LinkDestination-Sequenced
State Routing
Distance-Vector (DSDV)
(OLSR)
Energy
Reactive
protocols
Dynamic
Ad Hoc On-Demand
Source
Distance-Vector
Routing
(AODV)
(DSR)
Geography- Cluster-based
based routing (or hierarchical)
routing
GPSR
7
Routing protocol classification
 Route information mechanism
Proactive (table-driven)
 Reactive (demand-driven)
 Hybrid
 Temporal information
 Past vs. Future information
 Routing toplogy
 Flat vs. hierarchical
 Specific resources
 Geography or Power

8
Route update mechanism
 Proactive (or table-drive) protocols
 Determine routes independent of traffic pattern
 Traditional link-state and distance-vector routing protocols
• Destination Sequenced Distance Vector (DSDV)
• Optimized Link State Routing (OLSR)
 Reactive (or demand-drive) protocols
 Route is only determined when actually needed
 Protocol operates on demand
• Dynamic Source Routing (DSR)
• Ad hoc On-demand Distance Vector (AODV)
• Temporally Ordered Routing Algorithm (TORA)
 Hybrid Protocols
 Combine these behaviors (e.g., table in limited zone, and demand
drive otherwise)
• Zone Routing Protocol (ZRP)
• Greedy Perimeter Stateless Routing (GPSR)
9
10
Some general trade-offs
 Latency of route discovery

 Overhead of route discovery/maintenance
11
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
12
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
 Proactive protocols can (but not necessarily) result in
higher overhead due to continuous route updating
 Reactive protocols may have lower overhead
• Routes are determined only if needed
13
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
 Proactive protocols can (but not necessarily) result in
higher overhead due to continuous route updating
 Reactive protocols may have lower overhead
• Routes are determined only if needed
 Which approach achieves a better trade-off
depends on the traffic and mobility patterns
14
15
Ad hoc networks: terminology
 Broadcast: message sent to all neighbors
within range
 Flooding: message sent to all nodes in the
network by neighbors forwarding message
to their neighbors etc.
 Different from wired network!
16
17
Reactive protocols – DSR
 In a reactive protocol, how to forward a packet to
destination?

Initially, no information about next hop is available at all
18
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 all
neighbors – flood the network

19
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 all
neighbors – flood the network
Hope: At some point, packet will reach destination and an
answer is sent pack – use this answer for backward
learning the route from destination to source
20
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 all
neighbors – flood the network
Hope: At some point, packet will reach destination and an
answer is sent pack – use this answer for backward
learning the route from destination to source
 Practically: Dynamic Source Routing (DSR)
 Use separate route request/route reply packets 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
21
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
22
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
23
DSR: Route discovery (1)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
24
DSR: Route discovery (2)
Q
F
A
S
(S)
E
B
G
R
C
K
H
D
J
P
M
I
L
N
25
DSR: Route discovery (3)
(S,A)
Q
A
E
S
B
F
(S,E)
G
R
C
K
H
D
J
P
M
I
L
N
26
DSR: Route discovery (4)
Q
F
A
E
S
B
K
H
G
R
(S,E,G)
D
J
P
M
I
L
C
(S,B,C)
N
27
DSR: Route discovery (5)
Q
F
A
H
E
S
B
G
R
C
(S,A,F,H)
J
K
(S,E,G,J)
D
P
M
I
L
N
28
DSR: Route discovery (6)
Q
F
A
E
S
B
G
R
C
K
H
(S,A,F,H,K)
D
J
P
M
I
L
N
29
DSR: Route discovery (7)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
(S,A,F,H,K,P)
M
I
L
N
30
Route Discovery in DSR
 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
31
DSR: Route discovery (8)
Q
F
A
E
S
B
G
R
C
K
H
P
D
RREP(S,E,G,J,D)
J
M
I
L
N
32
DSR: RREP
 Route reply by reversing the route (as
illustrated) works only if all the links along
the route are bidirectional
 If unidirectional links are allowed, then
RREP may need a reverse route discovery
from D to S
 Note: IEEE 802.11 assumes that links are
bidirectional (since ACKs are used)
33
DSR: RREP (more text)
 Route Reply can be sent by reversing the route in
Route Request (RREQ) only if links are guaranteed
to be bi-directional

To ensure this, RREQ should be forwarded only if it
received on a link that is known to be bi-directional
 If unidirectional (asymmetric) links are allowed,
then RREP may need a route discovery for S from
node D


Unless node D already knows a route to node S
If a route discovery is initiated by D for a route to S,
then the Route Reply is piggybacked on the Route
Request from D.
 If IEEE 802.11 MAC is used to send data, then
links have to be bi-directional (since Ack is used)
34
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
35
DSR: Data delivery
Q
F
A
DATA(S,E,G,J,D)
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
36
37
Dynamic source routing (DSR)
 Reactive routing protocol
 2 phases, operating both on demand:
 Route discovery
• Used only when source S attempts to send a packet to
destination D
• Based on flooding of Route Requests (RREQ) and
replying with Route Reply (RREP)

Route maintenance
• Makes S able to detect, while using a source route to
D, if it can no longer use its route (because a link
along that route no longer works)
38
Dynamic source routing (DSR)
 Reactive routing protocol
 2 phases, operating both on demand:
 Route discovery
• Used only when source S attempts to send a packet to
destination D
• Based on flooding of Route Requests (RREQ) and
replying with Route Reply (RREP)

Route maintenance
• Makes S able to detect, while using a source route to
D, if it can no longer use its route (because a link
along that route no longer works)
39
DSR: Data delivery
Q
F
A
DATA(S,E,G,J,D)
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
40
DSR: Route maintenance (1)
Q
F
A
DATA(S,E,G,J,D)
E
S
B
G
R
C
K
H
X
D
J
P
M
I
L
N
41
DSR: Route maintenance (2)
Q
F
A
E
S
B
RERR(G-J)
G
R
C
K
H
X
D
J
P
M
I
L
N When receiving the Route Error message (RERR),
S removes the broken link from its cache.
It then tries another route stored in its cache;
if none, it initializes a new route discovery 42
43
DSR modifications, extensions
44
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
about topology 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, …
45
DSR: Optimization of route
discovery: route caching
 Principle: 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 D, 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
packets
46
Use of Route Caching
 When node S learns that a route to node D
is broken, it uses another route from its
local cache, if such a route to D exists in
its cache. Otherwise, node S initiates
route discovery by sending a route request
 Node X on receiving a Route Request for
some node D can send a Route Reply if node
X knows a route to node D
 Use of route cache can
speed up route discovery
 reduce propagation of route requests

 However, route caching has its downside
 stale caches can severely hamper the
performance of the network
47
DSR: Strengths
 Routes are set up and maintained only
between nodes who need to communicate
 Route caching can further reduce the
effort of route discovery
 A single route discovery may provide
several routes to the destination
48
DSR: Weaknesses
 Route requests tend to flood the network and
generally reach all the nodes of the network
 Because of source routing, the packet header size
grows with the route length
 Risk of many collisions between route requests by
neighboring nodes  need for random delays
before forwarding RREQ
 Similar problem for the RREP (Route Reply storm
problem), in case links are not bidirectional
Note: Location-aided routing may help reducing the
number of useless control messages
49
50
Destination Sequenced Distance
Vector Algorithm (DSDV)
DSDV is based on idea of classical BellmanFord Routing Algorithm
Each node maintains a routing table listing all available
destinations. The attributes of each destination are the
next hop, the number of hops to reach to the destination,
and a sequence number, which is originated by the
destination node.
Both periodic and triggered routing updates to
maintain table
51
Destination Sequenced
Distance Vector Algorithm
(DSDV)
1.
2.
Based on Bellman-Ford Next Hop Routing.
Each Node Maintains Tables for :
A. Next Hop on Path
B. Distance (in hops) to destination.
C. Sequence Number ( keep current route)
3. Nodes Exchange Updates With Neighbours
•

Full Routing Updates
Incremental Updates
52
Problems of Distance Vector
Pro-active routing based on Distance Vector
 Topology changes are slowly propagated

Count-to-infinity problem
 Moving nodes create confusion:
 they carry connectivity data which are wrong at
new place
 Table exchange eats bandwidth
53
DSDV
How DSDV addresses the problems?
 Tagging of distance information:
The destination issues increasing sequence number
 Other nodes can discard old/duplicate updates

 Changes are not immediately propagated

Wait some setting time
 Incremental updates instead of full table
exchange
54
55
Some general trade-offs
 Latency of route discovery

 Overhead of route discovery/maintenance
56
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
57
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
 Proactive protocols can (but not necessarily) result in
higher overhead due to continuous route updating
 Reactive protocols may have lower overhead
• Routes are determined only if needed
58
Some general trade-offs
 Latency of route discovery
 Proactive protocols may have lower latency
• Routes are maintained at all times

Reactive protocols may have higher latency
• Route from X to Y will be found only when X attempts to send to Y
 Overhead of route discovery/maintenance
 Proactive protocols can (but not necessarily) result in
higher overhead due to continuous route updating
 Reactive protocols may have lower overhead
• Routes are determined only if needed
 Which approach achieves a better trade-off
depends on the traffic and mobility patterns
59
60
GPSR
 Separate slides …
61
62
63
64
More stuff …
65
Route Reply in DSR
Y
Z
S
E
RREP [S,E,F,J,D]
F
B
C
M
J
A
L
G
H
K
I
D
N
Represents RREP control message
66
Data Delivery in DSR
Y
DATA [S,E,F,J,D]
S
Z
E
F
B
C
M
J
A
L
G
H
K
I
D
N
Packet header size grows with route length
67
Use of Route Caching
[S,E,F,J,D]
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
[J,F,E,S]
C
J
[C,S]
A
M
L
G
H
[G,C,S]
D
K
I
N
Z
[P,Q,R] Represents cached route at a node
(DSR maintains the cached routes in a tree format)
68
Use of Route Caching:
Can Speed up Route Discovery
[S,E,F,J,D]
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
C
[G,C,S]
[C,S]
A
[J,F,E,S]
M
J
L
G
H
I
[K,G,C,S] K
When node Z sends a route request
for node C, node K sends back a route
reply [Z,K,G,C] to node Z using a locally
cached route
D
RREP
N
RREQ
Z
69
Use of Route Caching:
Can Reduce Propagation of Route Requests
[S,E,F,J,D]
Y
[E,F,J,D]
S
[F,J,D],[F,E,S]
E
F
B
C
[G,C,S]
[C,S]
A
[J,F,E,S]
M
J
L
G
H
I
[K,G,C,S] K
D
RREP
N
RREQ
Z
Assume that there is no link between D and Z.
Route Reply (RREP) from node K limits flooding of RREQ.
In general, the reduction may be less dramatic.
70
Route Error (RERR)
Y
RERR [J-D]
S
Z
E
F
B
C
M
J
A
L
G
H
K
I
D
N
J sends a route error to S along route J-F-E-S when its attempt to
forward the data packet S (with route SEFJD) on J-D fails
Nodes hearing RERR update their route cache to remove link J-D
71
Ad Hoc On-Demand Distance
Vector Routing (AODV)
 As it is based on source routing, DSR includes




source routes in data packet headers
Large packet headers in DSR  risk of poor
performance if the number of hops is high
AODV uses a route discovery mechanism similar to
DSR, but it maintains routing tables at the nodes
AODV ages the routes and maintains a hop count
AODV assumes that all links are bi-directional
72
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
 Route Reply travels along the reverse path set-up
when Route Request is forwarded
73
Reactive protocols – AODV
 Ad hoc On Demand Distance Vector routing
(AODV)
Very popular routing protocol
 Essentially same basic idea as DSR for
discovery procedure
 Nodes maintain routing tables instead of source
routing
 Sequence numbers added to handle stale caches
 Nodes remember from where a packet came
and populate routing tables with that
information

74
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
75
AODV : Route discovery (1)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
76
AODV : Route discovery (2)
Q
F
A
E
S
B
G
R
C
: Route Request (RREQ)
K
H
D
J
P
M
I
L
N
Note: if one of the intermediate nodes (e.g.,
knows a route to D, it responds immediately
77 t
AODV : Route discovery (3)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
: represents a link on the reverse path
78
AODV : Route discovery (4)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
79
AODV : Route discovery (5)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
80
AODV : Route discovery (6)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
81
AODV : Route discovery (7)
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
82
AODV : Route reply and setup
of the forward path
Q
F
A
E
S
B
G
R
C
K
H
D
J
P
M
I
L
N
: Link over which the RREP is transmitted
: Forward path
83
Route reply in AODV
 In case it knows a path more recent than
the one previously known to sender S, an
intermediate node may also send a route
reply (RREP)
 The freshness of a path is assessed by
means of destination sequence numbers
 Both reverse and forward paths are purged
at the expiration of appropriately chosen
timeout intervals
84
AODV : Data delivery
Q
F
A
S
Data
E
B
G
R
C
K
H
D
J
P
M
I
L
N
The route is not included in the packet
header
85
AODV packets
 ROUTE REQUEST
 ROUTE REPLY
86
AODV : Route maintenance (1)
Q
F
A
S
Data
E
B
G
R
C
K
H
X
D
J
P
M
I
L
N
87
AODV : Route maintenance (2)
Q
F
A
RERR(G-J)
E
G
S
B
R
C
K
H
X
D
J
P
M
I
L
N
When receiving the Route Error message
(RERR),
S removes the broken link from its cache.
It then initializes a new route discovery.
88
AODV: Route maintenance
89
AODV: Destination sequence
numbers
 If the destination responds to RREP, it places its
current sequence number in the packet
 If an intermediate node responds, it places its
record of the destination’s sequence number in the
packet
 Purpose of sequence numbers:
 Avoid using stale information about routes
 Avoid loops (no source routing!)
90
1.
AODV : Avoiding the usage of
… Dtables S
stale
routing
…
S
A
A
2.
DSN(D) = 5
DSN(D) = 5
B
B
DSN(D) = 8
: Forward path
3.
S
A
RREQ
B
D
…
D
4.
S
DSN(D) = 5
RREP
B
DSN(D) = 8
D
A
…
DSN(D) = 5
DSN(D) = 8
91
AODV : Avoiding loops
A
B
S
X
D
C
: Forward pat
• Assume there is a route between A and D; link S-D breaks; assume A is not aware of this, e.g
RERR sent by S is lost
• Assume now S wants to send to D. It performs a RREQ, which can be received by A via path S
• Node A will reply since it knows a route to D via node B
• This would result in a loop (S-C-A-B-S)
• The presence of sequence numbers will let S discover that the routing information from A is
• Principle: when S discovers that link S-D is broken, it increments its local value of DSN(D). In
the new local value will be greater than the one stored by A.
92
AODV (unicast) : Conclusion
 Nodes maintain routing information only
for routes that are in active use
 Unused routes expire even when the
topology does not change
 Each node maintains at most one next-hop
per destination
 Many comparisons with DSR (via simulation)
have been performed  no clear conclusion
so far
93
Flooding of Control Packets
 How to reduce the scope of the route
request flood ?
Location Aided Routing LAR [Ko98Mobicom]
 Query localization [Castaneda99Mobicom]

 How to reduce redundant broadcasts ?
 The Broadcast Storm Problem [Ni99Mobicom]
94
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

95
Geographic Distance Routing
(GEDIR) [Lin98]
 Location of the destination node is assumed known
 Each node knows location of its neighbors
 Each node forwards a packet to its neighbor closest to
the destination
 Route taken from S to D shown below
H
A
S
D
B
E
F
C
G
obstruction
96
Geographic Distance Routing
(GEDIR) [Stojmenovic99]
 The algorithm terminates when same edge traversed
twice consecutively
 Algorithm fails to route from S to E
 Node G is the neighbor of C who is closest from
destination E, but C does not have a route to E
H
A
S
D
B
E
F
C
G
obstruction
97
Routing with Guaranteed
Delivery [Bose99Dialm]
 Improves on GEDIR [Lin98]
 Guarantees delivery (using location
information) provided that a path exists
from source to destination
 Routes around obstacles if necessary
 GPSR: A similar idea also appears in
[Karp00Mobicom]
98
QoS: Network layer solutions
 MAC protocols: bandwidth reservation,
real-time support only for link
 Network layer is host-to-host specific
resource negotiation
 reservation
 reconfiguration

 QoS routing protocols
 search for routes with resources that satisfy
QoS reqs
 find paths that consume minimum resources
99
QoS routing in ad-hoc networks
100
QoS-enabling routing protocols
h
Si = 1 (Li(m)), Li 
 Additive metrics:
Am =
P
 Concave metrics:
Cm = min(Li(m)), Li  P
 Multiplicative metrics: Mm =
h
P i = 1(Li(m)), Li  P
Two examples follow: ticket-based and QoSenabled AODV
101
A distributed ticket-based QoS
routing protocol for MANETs
 Chen and Nahrstedt (1999)
 Tolerates imprecise state information
during QoS route computation
 Probes multiple paths in parallel, limited by
tickets
 Optimality is explored
 Uses primary-backup-based fault tolerance
to reduce service interruption
102
QoS-enabled AODV
 QoS extensions in routing table:
 Maximum delay
 Minimum available bandwidth
 List of sources requesting delay guarantees
 List of sources requesting bandwidth
guarantess
103
QoS frameworks for MANETs
 Service model
 Routing protocol
 Resource reservation signaling
 Admission control
 Packet scheduling
104
QoS framework: Flexible QoS Model
for Mobile ad-hoc networks (FQMM)
105