Multi hop Connectivity in Mobile Ad hoc
Networks (MANETs)
Habib-ur Rehman
Institut für Betriebssysteme und Rechnerverbund
Technische Universität Braunschweig
Multi hop Connectivity
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Multi hop connectivity is solved for wired networks long ago
 Multi hop connectivity for wireless networks is also not new

Many routing protocols like AODV, DSDV, DSR, TBRF etc.
 Still no widely accepted solution as we have in wired networks
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
2/17
Proactive vs. Reactive
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Routing in MANETs

Proactive routing protocols
– maintain consistent and up-to-date information about the network by
constantly exchanging routing information among nodes

Reactive routing protocols
– initiate an independent route discovery process whenever a source
node requires a route to some destination
 Reactive approaches have less overhead but require
more time to connect source and destination


Reactive is preferable-more suits to low resource nature
Reactive route discovery requires some attention
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
3/17
On-demand behavior in AODV
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 On-demand Features


An approach based only on reaction to the offered traffic
A reactive protocol might have some proactive (not on-demand)
features
– In AODV, during the route discovery process, if an in-valid route
entry is already present in the routing table, the value of TTL field in
the RREQ packet’s IP header is initially set to the hop count value in
that entry.
 In AODV which is a reactive protocol, dependency on
proactive features or stale information is not beneficial
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
4/17
On-demand behavior in AODV
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 In these simulations

AODV with a reduced proactive feature vs. AODV
– Initial value of TTL field will not depend on existing stale entry

AODV with additional proactive feature vs. AODV
– Sharing of additional route information
S
I2
I1
I1
Knows
(S,
Add entry
forI1)(I1)
Knows (S)
I33
Knows
(S,
Add entry
)
for I(I
I
2 1, 2)
IIn
Add nentry
Knows (
for (I1,…,
S, In-1)
In-1)
Learning during Route Discovery
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
5/17
On-demand behavior in AODV
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Simulation Results







NS2.28 with AODV-UU
100 nodes
40 and 80 source/destination
pairs
Node speed 1 m/sec
Pause Time 0 seconds
CBR sources
UDP packets of 1024 Bytes
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
6/17
Some other Issues
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Broadcast transmissions



Used extensively in both Proactive and Reactive protocols for
maintaining routing tables
Is just not affordable
No RTS/CTS which means high risk of collision
 Scalability is the major problem in ad hoc networks



Number of nodes
Amount of mobility
Offered load
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
7/17
Ad hoc 802.11 MAC
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 A multi hop extension for IEEE 802.11 MAC header

It is a reactive or on-demand in nature

Exploit the normal MAC operations
– No special route/destination request packet/frame
– No special route/destination reply packet/frame

Exploits the use of data frame for destination discovery
– reduce the delay for connecting source to destination
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
8/17
Modifications to 802.11 MAC
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Additions to MAC header: Multi hop Data Frame (MDF)

Address1 = Recipient Address (RA)
Address2 = Transmitter Address (TA)
Address3 = Destination Address (DA)
Address4 = Source Address (SA)
An additional 2 Bytes cost field




– Hop count
Octets
S
2
2
6
6
6
2
6
0-2312
4
Frame
Control
Duration /
ID
Address 1
Address 2
Address 3
Address 4
RA
TARA
Sequence
Control
Frame
Body
FCS
RA TA DA SA
A S D S
A
TA DADASA
B A D S
B
RASATA DA SA
D B D S
Octets
D
2
Cost
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
9/17
Modifications to 802.11 MAC
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 A Forwarding Table is maintained by each node



Destination Address (6 Bytes)
Next Hop (6 Bytes)
Cost (2 Byte)
 All 802.11 frames carry unique sequence number and
fragment number in sequence control field (SCF)


Nodes maintain a list of MAC address (sender/TA) and SCF
value pairs
In Ad hoc 802.11 MAC, original sender is SA and not the TA
therefore in SCF list SAs should be stored
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
10/17
Protocol Components
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Three main components



Learning
Forwarding
Repair
 Learning: learning about accessible nodes

Whenever a node receives a multi hop data frame
– It adds entries in FWT for TA and SA of the frame if there is no entry
for either of them
– If there is already an entry for either, this entry will be updated
 A repair operation will be performed if the cost of previously stored path
is less than the new path
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
11/17
Protocol Components
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Forwarding

Originating data frames
– If there is an entry for DA in FWT
 TA would be the next hop in this entry
– Else TA would be broadcast

Relaying frames for other nodes
– If DA is broadcast and SCF is new
 Broadcast it once again
– If DA is uni-cast and SCF is new
 Follow same steps as in originating
– Frames carrying old SCF will always be dropped
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
12/17
Protocol Components
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Repair

Responsible for identifying anomalies in FWTS
Also share information about these anomalies with other nodes
Path Repair Frame (PRF)


– A multi hop data frame with no data in frame body
Octets
2
2
6
6
6
2
6
2
4
Frame
Control
Duration /
ID
RA
TA
DA
Sequence
Control
SA
Cost
FCS
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
13/17
Protocol Components
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 Possible situations for Repair operation

A node receives a data frame addressed to itself with RA as a
broadcast address
– A path repair frame will be sent
 RA in this frame would be broadcast
 SA and DA will be copied from the data frame just received
 The cost field will carry the SCF value of the data frame just received

A node receives a data frame addressed to itself through a path
which has higher cost than a path already known to it
– A path repair frame will be sent to SA on the previously (low cost)
known path

A node receives a data frame with RA as broadcast
– A path repair frame will be sent to TA if DA is known
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
14/17
Some Results
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 25 Nodes
 10 and 20

Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Normalized
Packet
MAC
Delivery
overhead(Bytes)
Ratio
Average
End
to End
Delay
for First Packet
1
0.9
0.8
0.7
Seconds
0.6
Bytes



Source/Destination pairs
Speed 1 m/sec
Pause Time 0 seconds
4 packets of 1024 bytes per
second generated by each
source. Max 10000 packets
CBR sources generating
UDP packets
0.5
0.4
0.3
0.2
0.1
0
3000
3.5
3
2500
2.5
2000
2
1500
1.5
1000
1
500
0.5
0 0
10connections
connections
1010
connections
20 connections
20
20connections
connections
15/17
Future Work
Problem Analysis
Ad hoc 802.11 MAC
Future Plans
 The initial simulation results show that scalability could
be a big challenge

A detailed analysis of network size, mobility, offered load
 Detailed analysis of different components and their
effects on performance
 Comparison with other well known routing protocols
 Possibility of different cost metrics
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
16/17
Thanks for your attention
Habib-ur Rehman
Institut für Betriebssysteme und Rechnerverbund
Technische Universität Braunschweig