Analysis of TCP Performance over Mobile Ad Hoc Networks

1
Analysis of TCP Performance over Mobile Ad Hoc
Networks

• Gavin Holland and Nitin Vaidya
• DCS, Texas AM University
• Presented by Rimon Barrfor cs615 on 18 Oct 2001

2
i n t r o d u c t i o n

• TCP
• throughput
• congestion control
• ad hoc networks
• mobility
• link breakage
• new metric expected throughput
• expected link failure notification (ELFN)

3
s i m u l a t e

• ns
• extended with 802.11
• half-duplex, shared channel
• random waypoint mobility model
• dynamic source routing (DSR)
• details
• 50 runs, 30 nodes, 1500x300m
• 2Mbps, 1460b packets, 250m range
• mobility 0.9v 1.1v

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d s r p r i m e r

• source routing
• route discovery
• route request/reply
• route error
• route caching
• packet salvaging
• redirect packet en-route

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t h r o u g h p u t

• throughput function of distance
• string topology
• expected throughput
• speed independent

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t h r o u g h p u t

• does not account for
• underlying routing decision
• routing overhead, esp. after failure

7
t h r o u g h p u t

• measured throughput degrades with speed
• high variability in throughput
• can get close to expected, when small number of
  link failures occur

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e x p l a n a t i o n

• caching of stale routes
• propagation of stale routes
• increased throughput with increased mobility!
• longer routes

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e x p l i c i t f e e d b a c k

• provide failure notification
• ICMP host unreachable
• piggy-back on DSR route failure
• TCP reaction to notification
• stand-by mode
• suspend retransmission timers
• ... until route re-established
• either probe or wait for notification

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e x p l i c i t f e e d b a c k
with feedback
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e x p l i c i t f e e d b a c k

• change probe intervals
• suggest function of round-trip time

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e x p l i c i t f e e d b a c k

• change congestion window
• little effect
• bandwidth/delay product is small
• short ramp-up
• change retransmission timeout
• had effect
• due to ARP packets dropped
• ... and then long timeout
• change choice of probe packet
• negligible effect

13
r e l a t e d w o r k

• ad hoc routing protocols
• performance of TCP over multi-hop
• TCP-Feedback protocol
• satellite communication protocols

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f u t u r e w o r k

• other underlying ad hoc routing protocols
• effect of link-layer
• i.e. retransmissions
• congested networks
• inter-layer interactions
• e.g. TCP ARP
• better cache management
• signal strength
• adaptive timeouts
• use of negative information

15
Analysis of TCP Performance over Mobile Ad Hoc
Networks

• Gavin Holland and Nitin Vaidya
• DCS, Texas AM University
• Presented by Rimon Barrfor cs615 on 18 Oct 2001