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Title: MANET:1/101

1
Routing and Broadcast in a Mobile Ad Hoc Network

Professor Yu-Chee Tseng
Dept. of Computer Science and information
Engineering
National Central University
(??? ???? ?????)

2
Outline

Introduction to Wireless Networks
Mobile Ad Hoc Network (MANET)
Routing in a Mobile Ad Hoc Network
Review
Fully Location-Aware Routing
Broadcast Storm Problem in MANET
MAC Introduction (IEEE 802.11 Background)

3
Introduction to Wireless Networks
4
When You Are Mobile Today

Desperately looking for a computer to check your
e-mails
Need to access Internet, WWW Info, etc.
Need cellular phone, airphone, pager, FAX, etc.
Using a laptop to do work while traveling
People of the late 20th century Keeping
connected any time, any where!!

5
Applications of Wireless Communications

Mobile Office/Meeting Room
with multitude of notebooks, palmtop, PDA, etc.
One who needs to work with customers face-to-face
doctor/nurse
clerk/salespersons
adv. paperless, less error-prone
Hospitality ???, ????, ????
Utility ???, ????
Kansas City wireless metering system.
Field work, Field services always on the road
Warehousing/Supermarket
pricing, order, bar-code input, etc.

6
Wireless Network Models

Wireless LAN infrastructured

Wireless LAN ad hoc

7
Wireless Network Models (cont.)

Cellular

Diffused (Infrared)

8
Wireless Network Models (cont.)

Wireless MAN

Wireless WAN

9
MANETMobile Ad Hoc Network
10
MANET

MANET Mobile Ad Hoc Networks
a set of mobile hosts, each with a transceiver
no base stations no fixed network infrastructure
multi-hop communication
needs a routing protocol which can handle
changing topology

11
Applications of MANET

battlefields (??)
nature disaster areas (????)
fleet in oceans
historical cites (??)
festival ground (??)

12
Related Information

IEEE 802.11 for Wireless LANs
MAC
PHY
IETF manet group
to stimulate research in this area
RFC 2503
Routing Protocols
unicast AODV, DSR, ZRP, TORA, CBRP, CEDAR
multicast AMRoute, ODMRP, AMRIS

13
Research Issues
GPS??
Application Layer
WWW
????
TCP/UDP
Multicast
GeoCasst
IP Layer
LA Routing
MAC Layer
Power Ctl
Channel Assignment
PHY Layer
CDMA
multi-code
14
Routing in a Mobile Ad Hoc Network
(Part I Review)

Ants Food Search
Reviews (DSR, ABR, SSR, LAR, TORA)

15
Ants Searching for Food
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16
(No Transcript)
17
Three Main Issues in Ants Search

Route Discovery
searching for the places with food
Packet Forwarding
delivering foods back home
Route Maintenance
when foods move to new place

18
Protocol 1DRS (Dynamic Source Routing)

on-demand
Source Routing
routes are denoted with complete information
(each hop is registered)
Two major parts
route discovery
route maintenance

19
Route Discovery of DSR

When a host has a packet to send, it first
consults its route cache.
If there is an unexpired route, then it will use
it.
Otherwise, a route discovery will be performed.
Route Discovery
A ROUTE_REQUEST packet is sent by flooding.
There is a route record field in the packet.
Each node will append its address to the record.

20
Route Request
Route Reply
21
Route Reply of DSR

A ROUTE_REPLY packet is generated when
the route request packet reaches the destination
an intermediate host has an unexpired route to
the destination
A route is then generated in two manner
from destination
the route traversed by the ROUTE_REQUEST packet
from intermediate host
the route traversed by the ROUTE_REQUEST packet
concatenated with the route in the intermediate
hosts route cache

22
Path of ROUTE_REPLY

Which way should be taken by the ROUTE_REPLY?
Two possibilities
symmetric path
follow the same route in the reverse order to
reach the source
asymmetric path
need to discover a new route to the source by
initiating a ROUTE_REQUEST to the source
piggyback the discovered route to the
ROUTE_REQUEST packet

S
D
23
Route Maintenance of DSR

When the data link layer encounters a link
breakage, a ROUTE_ERROR packet will be initiated.
The packet will traverse in the backward
direction to the source.
The source will then initiate another
ROUTE_REQUEST.
Maintenance of route cache
All routes which contain the breakage hop have to
be removed from the route cache.

S
D
24
How to Detect a Link Breakage

Active Acknowledge
The receiver of a packet actively sends an ACK to
the sender.
Passive Acknowledge
The sender passively listen to the receivers
sending.

S
R
S
R
V
data packets active/passive ACK
25
Protocol 2 ZRP

ZRP Zone Routing Protocol
A hierarchical approach
zone the area that a node knows the complete
routing information
so routing goes in a zone-to-zone basis

26
Protocol 3 ABR(Associativity-Based Routing)

ABR considers the stability of a link.
Basic Idea
Each node periodically generates a beacon to
signify its existence.
On receipt of the beacon, a node increases the
tick of the sender by 1.
A higher degree means more stability.
A lower degree means less reliable.
When a link becomes broken, the node will set the
tick of the other node to 0.

27
ABR Outline

Route Discovery
(similar to DSR)
On needing a route, a host will broadcast a
ROUTE_REQUEST packet.
Each receiving host will append its address to
the packet.
The ticks will be appended in the ROUTE_REQUEST
packet.
The destination node will select the route with
the highest tick.

7
5
8
source
destination
10
4
28

Route Maintenance
On route error, a node will perform a local route
search.
in hope of rebuild the path locally.
If the local search fails, a ROUTE_ERROR will be
reported to the source.

source
local searched zone
destination
29
Protocol 4 SSR(Signal Stability Routing)

Observation
The ABR only considers the stability to nodes.
Two more metrics
signal strength
the strength of a signal
provided by link layer
location stability
how fast a host moves
could be measure by
the change of signal strength over a period of
time
location devices (such as GPS)

30
Protocol 5 Location-Aided Routing (LAR)

to limit the area to search for the route
I will forward the ROUTE_REQ
J will not forward the ROUTE_REQ.

A
B
D
J
I
Expected zone of D
S
C
Route search zone
31
Assumption of LAR

Location Device is available.
outdoor positioning device
GPS global positioning system
accuracy in about 20 to 50 meters
indoor positioning device
Infrared
short-distance radio, bluetooth, etc.

32
Protocol 6 TORA (Temporally Ordered Routing
Algorithm)

source-initiated protocol
provide multiple paths for any source-destination
pair
Like water flowing, it goes from upstream to
downstream.
for highly dynamic mobile networks

33
Main Idea

Regard the network as a directed graph.
For each destination, a DAG (directed acyclic
graph) will be maintained.
Note There are n copies of DAGs, each
associated with one destination, where n is the
number of hosts.
In the following discussion, we only discuss one
DAG associated with a destination.
The DAG is accomplished by assigning each node i
a height metric hi.
A link from i to j means hi gt hj.

34
Full Reversal Method

A node will update its height to adapt to the
change of network topology.
Height hi (valuei, IDi)
a node will change its value to change the
direction of a link
Relation hi gt hj if the following is true
valuei gt valuej
(valuei valuej) and (Di gt Dj)
Ex (5, 4) gt (4, 6)
Ex (5, 4) gt (5, 2)
Property Given any to heights, there must exist
a gt relation between them.

Rule
Each node other than the destination that has no
outgoing links reverses the direction of all its
incoming links.
This means that the nodes height is a local
minimum.
This is done by getting a larger height such that
the node becomes a local maximum.
MAXall neighbors heights 1

a, 5
b, 6
e, 3
d, 4
f, 1
c, 3
dest, 8
g, 2
36
a, 7
b, 6
e, 6
original
a, 5
d, 9
f, 7
c, 9
b, 6
e, 3
dest, 8
g, 5
d, 4
f, 1
c, 3
a, 5
dest, 8
g, 2
b, 6
e, 6
d, 4
f, 4
c, 9
a, 5
b, 6
e, 3
dest, 8
g, 5
d, 4
f, 4
c, 9
dest, 8
g, 2
37
a, 7
b, 10
e, 10
d, 9
f, 7
c, 9
dest, 8
g, 10
a, 11
b, 10
e, 10
d, 9
f, 11
c, 9
dest, 8
g, 10
Eventually, the DAG will stablize.
38
TORA Summary

There will exist multiple paths leading to a
destination.
Note
The above DAG is associated with node dest.
Associated with each node, there is a DAG.
The above scheme is called Full Reversal.
In TORA, more complicated rules are used.
Partial reversal
Temporally-ordered routing
Height metric

39
Routing in a Mobile Ad Hoc Network (Part II
Fully Location-Aware Routing)

GRID A Fully Location-Aware Routing Protocol
for Mobile Ad Hoc Networks,
Telecommunication Systems (to appear)

40
Basic Idea

Adopt Positioning Systems
such as GPS receivers
President Clinton ordered to discontinue SA
(selective availability) in May 2000
will increase the accuracy by an order
Fully utilize location information
route discovery
data forwarding
route maintenance
We propose a new protocol called GRID.

41
Observation 1

Determine route quality based on location
information
passing B is better than passing A

42
Observation 2

Improving the vulnerability and quality of a
route based on location information
When B moves away, E can work on behalf of B.
When F roams in, using F is more reliable.

43
Comparison of Using Location Information
Scheme Route Discovery Packet Relay Route Maintenance
DSR ? ? ?
AODV ? ? ?
ZRP ? ? ?
LAR ? ? ?
GRID ? ? ?
44
The GRID Routing Protocol

Partition the physical area into d x d squares
called grid.

45
Protocol Overview

In each grid, a leader will be elected, called
gateway.
Routing is performed in a grid-by-grid manner.
Responsibility of gateway
forward route discovery packets
propagate data packets to neighbor grids
maintain routes which passes the grid

46
Route Search

We can adopt any existing route discovery
protocol.
Major features/differences
limit the search range by the locations of source
and destination
only gateway will help with the discovery process
The more crowded the area is, the more saving.
routing table is indicated by grid ID (instead of
host address)

47
Route Search Example

route search
route reply

48
Route Search Range Options
49
Routing Table Format

Next-hop routing
the next hop is identified by grid ID

Node S B E F D
Destination D D D D D
Next hop (2, 2) (3, 2) (4, 2) (5, 3) null
50
Route Maintenance

Two issues
how to maintain a gateway in each grid
how to maintain a grid-by-grid route
Special Feature
longer route lifetime
as long as there is a host in each gateway, a
route will be alive
more robust
In existing protocols, once a node in the route
roams away, the route will be broken.

51
Gateway Election in a Grid

Any leader election protocol in distributed
computing can be used.
Weaker than leader election
It is acceptable that there are multiple leaders
in a grid.
less acceptable without leader
Preference in electing a gateway
near the physical center of the grid
likely to remain in the grid for longer time
once elected, a gateway will remain as so until
leaving the grid
to avoid ping-pong effect

X
52
Gateway Election Details
BID(g, loc)
GATE(g, loc)
RETIRE(g, T)
53
How to Maintain a Grid-by-Grid Route

Strength more robust route
mobility-resistant
Problems
Gateway moves away
The gateway election will find the new gateway.
So the route will remain alive.
Source moves away (see next page)
getting closer
getting farther away
Destination move away (similar)

54
(No Transcript)
55
Relationship of Grid Size and Transmission
Distance

r radio transmission distance
d grid size

56
Simulation Model

Physical area of size 1000m?1000m
n number of hosts 100300
r300m
d grid size
GRID-1
GRID-2
GRID-3
Roaming speed 30 km/hr, 60 km/hr

57
Route Lifetime

With better route maintenance, our route lifetime
is longer.
30 km/hr
60 km/hr

58
Routing Cost (s30 km/hr)

n 100, 200, 300
(number of hosts)
GRID is better in
more crowded area.

59
Delivery Rate

With less routing cost (and thus less traffic
load), our packets can be delivered with higher
success rate.
30 km/hr
60 km/hr

60
Route Length

Limited by gateway positions, the route length
could be longer for GRID approach.
30 km/hr
60 km/hr

61
Conclusions

A FULLY location-aware routing protocol
route discovery by gateways only
data forwarding by gateway ID, instead of host
ID
route maintenance like handoff in GSM systems
Taking advantage of geometric property of
network.
instead of graph property in other approaches
Less routing cost
longer route lifetime, more resilient route
less traffic load

62
The Broadcast Storm Problem in MANETs
63
Storms of Nature
64
T-Storm in St. Louis
65
Touchdown of a Tornado
66
Can Human Create Storms?
67
The Storms in the Internet

Subject ??????????Email??,??? NT3000?!
Date Sun, 11 Jul 1999 184721 0800
(CST)
From _at_.university.edu
To ltyctseng_at_csie.ncu.edu.twgt
???????
????????????,?????????????!
??!??! ??????????Email??,??? NT3000?!!!
?????????,?????????????????,
??????????????!!!
????????????,????????!!!
??????????????????????!!!
???,??????????,???????????,
???????????????!!!
(a 3-page long email ...)

68
Call for Papers

Dear Friends,
Sorry if you receive the duplicate messages.
But please distribute the following message to
your friends.
Prof. , University of
Call for Papers
International Conference on ????
IC???'99
to be held in ???, ???, September ???,
1999
http//www.???/conf/ic???99
THEME
Research on mobile computing is gaining more and
more attention ...
...

69
The Storms in the Internet
70
Broadcast Problem

Broadcast the sending of a message to other
hosts
Ex Route search in a MANET
Ex DSR, AODV, ZRP protocols.
Assumptions
The broadcast is spontaneous.
no synchronization
no prior global topology knowledge
The broadcast is unreliable.
no acknowledgement of any kind
not to cause more contention
100 reliability is unnecessary for some
application
No RTS/CTS dialogue.

71
Broadcast by Flooding

A straight-forward approach
A host rebroadcasts the message on receiving a
broadcast message for the first time.
Broadcast storm problem
redundant rebroadcasts
contention problem
collision problem

72
Serious Redundancy

Optimal broadcasting vs. Flooding
(a) optimal 2 steps
(b) optimal 2 steps

Severity of Redundant Coverage.

73
Analysis on Redundancy

Additional Coverage provided by a rebroadcast.
The max. additional coverage is 61.
The coverage is 41 in average.

The expected additional coverage EAC(k)/?r2 after
a host heard a broadcast message k times.

74
Analysis on Contention

When a host broadcasts, its neighbors are likely
to contend with each other for the medium.
A gt B, C, D
B, C, D could seriously contend with each other.

cf(n, k) The probabilities of having k
contention-free hosts among n receiving hosts.

B
A
C
D
75
Analysis on Collision

Higher Possibility of Collision
Rebroadcasts are likely to start at the same
time.
Backoff window runs out if medium is quiet for a
while.
lack of RTS/CTS dialogues
lack of collision detection (CD) if collision
occurs
hidden terminal problem

76
Broadcast Storm Problem Summary

Redundancy
Contention
Collision
How to derive an efficient scheme for
broadcasting in a MANET?

77
Possible Broadcast Solutions

Probabilistic Scheme
Counter-Based Scheme
Distance-Based Scheme
Location-Based Scheme
Cluster-Based Scheme

78
Probabilistic Scheme

Rebroadcast by Tossing a Die
A host always rebroadcasts with a certain
probability P.
When P 1, this is flooding.
A smaller P will reduce the storm effect.

79
Simulation Parameters

no of hosts 100
transmission radius 500 meters
packet size 280 bytes
transmission rate 1 M bits/sec
broadcast arrival rate 1 per sec. to the whole
map
map (1 unit 500 meters)
1x1, 3x3, 5x5, 7x7, 10x10
roaming pattern random walk
speed 010 km/hr in a 1x1 map, 030 km/hr in a
3x3 map, etc.
IEEE 802.11 without PCF (point coordination
function)

80
Performance of Probabilistic Scheme

RE REachability (in lines)
SRB Saved ReBroadcast (in bars)

Latency
81
Observation

Reachability
In smaller maps, a low P is sufficient to achieve
high reachability.
A larger P is needed in a larger map.
Saved Rebroadcast
linear with respect to P
Latency
Interestingly, in smaller areas, broadcast tends
to complete in a slower speed.

82
Counter-Based Scheme

If a host has received a broadcast packet gt C
times,
then do not rebroadcast.
Examples Addition Coverage
1 time gt 41
2 times gt 19
3 times gt 9
4 times gt 5
gt 4 times, very little extra area

83
Performance of Counter-Based Scheme

We vary C 2, 3, ..., 6 to observe the
performance.
A larger C means more rebroadcast.

84
Observation

Reachability
C gt 3 can offer a reachability close to
flooding.
Saved Rebroadcast
In denser area, there is more saving. In sparser
area, there is less saving.
Latency
Higher latency is smaller area.

85
Distance-Based Scheme

Calculate the distance to the sending host.
dmin Minthe distance to each sending host
If dmin lt D (a threshold), then do not
rebroadcast.
How to find distance
signal strength
GPS devices

86
Performance of the Distance-Based Scheme

We vary D 147, 72, 37, 20, 11 to observe the
effect.
Smaller D means more rebroadcasting.

87
Observation

Why choosing D147?
addition coverage 0.187, equal to that of C2
Reachability
All look good, close to flooding.
Saved Rebradcast
not much
Latency
smaller area has higher latency

88
Location-Based Scheme

From GPS to obtain the senders location.
Let (x1, y1), (x2, y2), (x3, y3), ..., (xk, yk)
be locations of senders.
We can accurately calculate the additional
coverage of this rebroadcast.

No Extra Coverage
Some Coverage
S2
A
S1
A
S1
S3
S2
89
Difficulty

Involve complicated math to calculate the extra
coverage.
A lot of calculus!
Approximation
grid simulation

S1
A
S3
S2
90
Performance of the Location-Based Scheme

We vary A (addition coverage) from 0.1 to 0.01.
Smaller A means more rebroadcast.

91
Observation

Why choosing A0.187?
This is additional coverage offered by C2.
Best performance over all the above schemes!

92
Modified Location-Based Schemes

Polygon Test
If a node is within the polygon formed by the
locations of senders, then DO NOT rebroadcast.
(Fig. (a))
Otherwise, rebroadcast. (Fig. (b))
If a host is within the convex, the maximum
additional coverage is well below 22. (Fig. (c))

93
A Short Summary

Main Concern
Extra coverage of a rebroadcast
Different levels of accuracy
probabilistic, counter, distance, location,
polygon
Performance
Flooding lt Probabilistic Scheme lt Counter-Based
Scheme lt Distance-Based Scheme lt Location-Based

94
Relationship between Reachability and Saving