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How bad TCP suffers from packet losses and delays over wireless ad hoc network
May Zin Oo, Mazliza Othman
Faculty of Computer Science & Information Technology University of Malaya Malaysia
3rd to 5th April
Outlines
‡ What does Ad hoc network mean?
‡ Applying TCP (Transport Layer Protocol) to Ad hoc
network
‡ TCP Variants for Ad hoc network
‡ Ad hoc routing protocols
‡ Simulation Methodology
‡ Experimental results from simulations
‡ Conclusion
‡ Self organizing, self healing, distributed
networks
† The wireless devices can communicate
each other without using central access
points in peer-to-peer fashion , but these
are within range of each other.
‡ Decentralized wireless network
† The determination of which nodes
forward data is made dynamically based
on the network connectivity.
AD HOC NETWORK
Applying TCP to Ad Hoc Environment
‡ TCP (Transmission Control Protocol)
† To provide flow control, congestion control & avoidance, in-
order and reliable end-to-end delivery of data packet in the
wired networks.
‡ Applying TCP to ad hoc environment,
† TCP has to face many problems such as packet losses due to
congestion and node mobility, wireless high bit errors, and so
on.
‡ Because of these problems, the following TCP versions were
intended for wireless environment:
† Tahoe, Reno, NewReno, Vegas and Westwood
TCP Versions for Ad Hoc Network
‡ TCP Tahoe introduced slow start and congestion avoidance.
† Slow start,
† Use at the beginning of a transfer or after timeout
† Start from minimum window size
† Increase window size exponentially
† Congestion avoidance,
† Increase congestion window size by MSS/cwnd bytes for
each ACK received.
† Increase window size linearly
‡ In our simulation, I will analysis the following TCP variants.
† NewReno
† Vegas
† Westwood.
NewReno Vegas Westwood
Features
● Slow start● Congestion
Avoidance● Fast Retransmit● Fast Recovery
● Slow Start● Congestion
Avoidance● Rerouting● Persistent
Congestion
● A sender-side modification of the TCP congestion window algorithm
Loss Detectio
n
● Three duplicate ACKs
● Half the congestion window
● Perform Fast retransmit & Fast recovery
● Go slow start if ACK times out
● One duplicate ACK ● Compare timestamp
of ACK to a timeout value
● Retransmit rather than wait for three duplicate ACKs if timestamp is greater than the timeout value
● Three duplicate ACK● End-to-end
bandwidth estimation to discriminate the cause of packet loss
● Use this estimate to compute congestion window and slow start
Comparison of three variants of TCP
Ad hoc routing protocols
Table-driven
DSDV
CGSR
WRP
Source-initiated on-demand
AODV
DSR
LMRTORA
ABR
SSR
Ad Hoc Routing Protocols
DSDV DSR AODV
● Hop by hop Distance Vector
● Loop freedom
● Per node routing table
Destination Next hop Number of hops Sequence
number
● Source routing● Each packet:
complete route
● Route Discovery● Route Maintenance● Caching
optimizations
● Like DSR On demand route
discovery, maintenance● Like DSDV
hop by hop routing, route sequence numbers
● Route Request● Route Reply
Number of hops to destination
● Maintenance Periodic HELLO
Ad Hoc Routing Protocols
‡ Network Simulator (NS-2) was used to study the three variants of TCP over three ad hoc routing protocols.
Ad hoc environment Static and mobile ad hoc networks
Simulation period 540 seconds
Simulation scenario 5 nodes & 15 nodes chain topology
Simulation topology 2300 m x 1000 m
Transmission range of each node 150 m
Bandwidth 11Mbps
Traffic FTP (File Transfer Protocol)
Packet size 1500 bytes
Simulation Methodology
0 1 2 3 4
0 1 2 3 4
1 2 3
0 1 2 3 4 5 6 7 14
…
0 2
2 12
12
6
7
7 8 14
… …… …
Static ad hoc environment ( 5 nodes & 15 nodes )
Mobile ad hoc environment ( 5 nodes & 15 nodes )
Fig 1: Source node 0 connects to destination node 4 in static ad hoc
network
Fig 2: Source node 0 connects to destination node 4 in mobile ad hoc network
Fig 3: Source node 0 connects to destination node 14 in static ad hoc network
Fig 4: Source node 0 connects to destination node 14 in mobile ad hoc network
Simulation Methodology (Continued…)
Simulation Results
‡ We simulate each variant of TCP over each routing
protocol in static ad hoc network and mobile ad hoc
network environments and measure how the node
mobility affects TCP and routing protocols in 5-node and
15-node chain topologies.
‡ We have analyzed † Packet loss rates (%) † Data transfer rate† Throughput of received packets at the destination
node.
Packet loss rate (%) measurement of DSDV
5 nodes 15 nodes0
0.5
1
1.5
2
2.5
3
3.5
4
New
Ren
o;
0.5
80
00
00
00
00
00
01
New
Ren
o;
3.3
6
Veg
as;
0
.02
00
00
00
00
00
00
01
Veg
as;
0
.89
00
00
00
00
00
00
1
West
wood
; 0
.13
West
wood
; 0
.45
Packet loss rate (%) using DSDV in static ad hoc network
5 nodes 15 nodes0
0.5
1
1.5
2
2.5
3
3.5
4
New
Ren
o;
0.3
4
New
Ren
o;
2.6
5
Veg
as;
0.0
3
Veg
as;
0.0
9
West
wood
; 0
.58
West
wood
; 0
.71
00
00
00
00
00
00
1
Packet loss rate (%) using DSDV in mobile ad hoc network
Figure 1
Figure 2
Packet loss rate (%) measurement of AODV
5 nodes 15 nodes0
0.5
1
1.5
2
2.5
3
3.5
4
New
Ren
o;
0.1
1
New
Ren
o;
3.6
8
Veg
as;
0.0
3 Veg
as;
1.6
3
West
wood
; 0
.09
West
wood
; 0
.36
Packet loss rate (%) using AODV in static ad hoc network
5 nodes 15 nodes0
0.5
1
1.5
2
2.5
3
3.5
4
New
Ren
o;
0
New
Ren
o;
3.5
2
Veg
as;
0 Veg
as;
1.0
7
West
wood
; 0
.41 W
est
wood
; 1
.49
Packet loss rate (%) using AODV in mobile ad hoc network
Figure 3
Figure 4
Packet loss rate (%) measurement of DSR
5 nodes 15 nodes0
5
10
15
20
25
30
35
New
Ren
o;
30
.26
New
Ren
o;
18
.06
Veg
as;
3.7
5
Veg
as;
2.4
2
West
wood
; 0
.13
West
wood
; 0
.45
Packet loss rate (%) using DSR in static ad hoc network
5 nodes 15 nodes0
5
10
15
20
25
30
New
Ren
o;
27
.69
New
Ren
o;
18
.81Veg
as;
3.6
3
Veg
as;
5.0
6
West
wood
; 0
.96
00
00
00
00
00
00
1
West
wood
; 3
.45
Packet loss rate (%) using DSR in mobile ad hoc network
Figure 5
Figure 6
DSDV DSR AODV0
2
4
6
8
10
12
14
Data transfer rate of Vegas over NewReno
5 nodes
15 nodes
Data
tra
nsf
er
rate
(ti
mes)
Comparison of data transfer rate in static environment
‡ Vegas is the fastest data transfer rate under various conditions.
Figure 7
Figure 8
DSDV DSR AODV0
2
4
6
8
10
12
14
Data transfer rate of Vegas over Westwood
5 nodes
15 nodes
Data
tra
nsf
er
rate
(ti
mes)
DSDV DSR AODV0
2
4
6
8
10
12
14
Data transfer rate of Vegas over NewReno
5 nodes
15 nodes
Data
tra
nsf
er
rate
(ti
mes)
Comparison of data transfer rate in mobile environment
Figure 9
Figure 10
DSDV DSR AODV0
2
4
6
8
10
12
14
Data transfer rate of Vegas over Westwood
5 nodes15 nodes
Da
ta t
ran
sfe
r ra
te (
tim
es)
‡ All TCP variants over DSDV routing protocol can still receive packets
although nodes move out of each other’s transmission range.
‡ This is because DSDV maintains all possible routes to the destination.
‡ Although DSR routing protocol suffer from most packet losses, the
number of received packets at destination nodes are the most.
Measurement of the throughput in mobile ad hoc network
Conclusion
Packet loss rate (%)
Static ad hoc network Mobile ad hoc network
5 nodes 15 nodes 5 nodes 15 nodes
DSDV Vegas Westwood Vegas Vegas
AODV Vegas Westwood NewReno & Vegas Vegas
DSR Westwood Westwood Westwood Westwood
In the overview of performance comparison , according to the packet
loss rate (%) ,
‡ NewReno over AODV routing in mobile environment but in less
nodes,
‡ Vegas over DSDV and AODV routing in both environment and
‡ Westwood over DSR routing in both environment are the best and
least packet loss rate.