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
Experimental results from simulations
Conclusion AD HOC NETWORK 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. 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.
Use at the beginning of a transfer or after timeout
Start from minimum window size
Increase window size exponentially
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.
Westwood. Comparison of three variants of TCP
Ad Hoc Routing Protocols
Ad Hoc Routing Protocols
Simulation Methodology Network Simulator (NS-2) was used to study the three variants of TCP over three ad hoc routing protocols. 1
2 3 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 Simulation Methodology (Continued…) Static ad hoc environment ( 5 nodes & 15 nodes ) … 5 6 7 14 Fig 1: Source node 0 connects to destination node 4 in static ad hoc network Fig 3: Source node 0 connects to destination node 14 in static ad hoc network 2 7 12 Mobile ad hoc environment ( 5 nodes & 15 nodes ) … … … … 2 6 7 0 12 8 14 Fig 2: Source node 0 connects to destination node 4 in mobile ad hoc network Fig 4:Source node 0 connects to destination node 14 in mobile ad hoc network
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
Figure 1 Figure 2
Packet loss rate (%) measurement of AODV Figure 3 Figure 4
Packet loss rate (%) measurement of DSR Figure 5 Figure 6
Comparison of data transfer rate in static environment Figure 7 Vegas is the fastest data transfer rate under various conditions. Figure 8
Comparison of data transfer rate in mobile environment Figure 9 Figure 10
Measurement of the throughput in mobile ad hoc network 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. Conclusion 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.