Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)

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Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)

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Multi hop Connectivity in Mobile Ad hoc Networks (MANETs) Habib-ur Rehman –

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Title: Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)

1
Multi hop Connectivity in Mobile Ad hoc Networks
(MANETs)

Habib-ur Rehman

2
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

3
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

4
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
packets 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

5
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

Learning during Route Discovery
6
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

7
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

8
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

9
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

10
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

11
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

12
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

13
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
4
2
6
2
6
6
6
2
2
FCS
Cost
SA
Sequence Control
DA
TA
RA
Duration / ID
Frame Control
14
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