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Institut für Betriebssysteme und RechnerverbundTechnische Universität Braunschweig
Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
2/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Multi hop Connectivity
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
3/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Proactive vs. Reactive
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
4/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
On-demand behavior in AODV
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
5/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
On-demand behavior in AODV
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 I1Knows (S)
I2Knows (S,
I1)
InKnows (S, In-1)
I3Knows (S,
I2)
Problem Analysis Ad hoc 802.11 MAC Future Plans
Learning during Route Discovery
S I1I2
Add entryfor (I1)
InAdd entryfor (I1,…,
In-1)
I3Add entryfor (I1, I2)
6/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
On-demand behavior in AODV
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
7/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Some other Issues
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
8/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Ad hoc 802.11 MAC
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
9/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Modifications to 802.11 MAC
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
Octets
FCSFrame Body
Address 4
SASequence Control
Address 3
DAAddress 2
TAAddress 1
RADuration / ID
Frame Control
40-23126266622
Octets
Cost
2
DS A BRA TA DA SAA S D S
RA TA DA SAD B D S
RA TA DA SAB A D S
10/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Modifications to 802.11 MAC
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
11/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Protocol Components
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
12/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Protocol Components
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
13/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Protocol Components
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
Octets
FCSCostSASequence ControlDATARA
Duration / ID
Frame Control
426266622
14/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Protocol Components
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
15/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Some Results
25 Nodes 10 and 20
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
Normalized MAC overhead(Bytes)
0
500
1000
1500
2000
2500
3000
Byt
es
10 connections 20 connections
Problem Analysis Ad hoc 802.11 MAC Future Plans
Packet Delivery Ratio
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
10 connections 20 connections
Average End to End Delay for First Packet
0
0.5
1
1.5
2
2.5
3
3.5
Sec
on
ds
10 connections 20 connections
16/17Multi hop Connectivity in Mobile Ad hoc Networks (MANETs)
Habib-ur Rehman
Future Work
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
Problem Analysis Ad hoc 802.11 MAC Future Plans
Institut für Betriebssysteme und RechnerverbundTechnische Universität Braunschweig
Thanks for your attention
Habib-ur Rehman