17/10/2003TCP performance over ad-hoc mobile networks. 1 LCCN – summer 2003 Uri Silbershtein Roi Dayagi Nir Hasson

17/10/2003TCP performance over ad-hoc mobile networks. 2 Presentation content. Purpose of this project. Ad-hoc mobile networks overview. TCP Configurations used. Mobile networks routing protocols. Simulation methodology Simulation results. Conclusions.

17/10/2003TCP performance over ad-hoc mobile networks. 3 Purpose of this project. Look for TCP configurations networks in an end to end approach,that improve ad-hoc mobile networks throughput. Test TCP configurations over several routing protocols in an ad-hoc mobile network. Test TCP configurations over different ad-hoc mobile environment. TCP configurations were limited to those which are supported by the ns.

17/10/2003TCP performance over ad-hoc mobile networks. 4 Ad-hoc mobile networks overview. Unlike most of portable communication, ad-hoc network does not have fixed base stations. The network topology is in general dynamic. TCP was original designed to static networks. Each node in a wireless ad hoc network functions both as a host and as a router. Ad-hoc mobile networks examples: natural disasters, military settings.

17/10/2003TCP performance over ad-hoc mobile networks. 5 Tested TCP configurations. Selective acknowledgments (SACK) and Delayed ACK. Explicit Congestion Notification. (ECN) Limited Transmit. (LT)

17/10/2003TCP performance over ad-hoc mobile networks. 6 Tested TCP configurations. Selective acknowledgments (SACK) and Delayed ACK. –High probability that some of the packets from the same sending window will be corrupted.(high bit error rate) –By using selective ACK option we can ensure packets that were received by the destination successfully, will not be send again. Explicit Congestion Notification. (ECN) Limited Transmit. (LT)

17/10/2003TCP performance over ad-hoc mobile networks. 7 Tested TCP configurations. Selective acknowledgments (SACK) and Delayed ACK. Explicit Congestion Notification. (ECN) TCP relies on packet drops as the indication of congestion. ECN idea is that the router will signal the development of the congestion before a packet has to be discarded. In ad-hoc mobile networks, each node serves as a router, and therefore can notify to the sources about its congestion. In this way loss of packets because of congestion could be avoided. In mobile topology there is high probability to congestion, occurs due to bottleneck nodes. Limited Transmit. (LT)

17/10/2003TCP performance over ad-hoc mobile networks. 8 Tested TCP configurations. Selective acknowledgments (SACK) and Delayed ACK. Explicit Congestion Notification. (ECN) Limited Transmit. (LT) LT algorithm: when two consecutive ACKs for the same segment are received, a new segment is transmitted if the ordinary conditions fulfilled. The main idea is to trigger the Fast Retransmit algorithm. This is helpful in cases where the congestion window is too small for the sender to receive three duplicate ACKs - Avoid Retransmission Timeouts (RTOs).

17/10/2003TCP performance over ad-hoc mobile networks. 9 Mobile networks routing protocols. DSR and DSDV were the main routing protocols used over the project. DSR considered to have the second best performance over ad-hoc networks, according to research done by IBM labs. Another routing protocols that was tested are AODV,DSDV and TORA. Our main problem was the ns limits – it does not support SSA routing protocol and some routing protocols do not support ECN feature.

17/10/2003TCP performance over ad-hoc mobile networks. 10 Simulation methodology. We fixed crucial environment parameters, that effect dramatically the TCP performance over ad- hoc mobile networks. Those environment parameters are: area size. – area size. – total number of nodes. – number of sources. – nodes velocity.

17/10/2003TCP performance over ad-hoc mobile networks. 11 Simulation methodology (cont). The following environment parameters were used over our scenarios: –Area size: 500m*400m, 600m*400m,1500m*1000m. –Total number of nodes: 25 and 10. –Number of sources: 10, 6 and 1. –Nodes’ velocity: 30m\s, 15m\s and 5m\s (108km\h, 54km\h, 18km\h). Scenario run time was 200 sec and 100sec. Because we want to test ECN in mobile network, we had to use ns 2.26 version which is very sensitive and limiting regarding the value of the environment parameters.

17/10/2003TCP performance over ad-hoc mobile networks. 12 Simulation methodology (cont). Automatic Script Generator (ASG). In order to have large amount of results over random scripts, an automatic script generator was developed. Using that tool we were able to run over total of 1000 random scenarios...\vb\Project1.1.2.exe

17/10/2003TCP performance over ad-hoc mobile networks. 13 Simulation methodology (cont). Throughput Calculation(in general) The formula for calculation is the sum of the total TCP packets (in bytes), which were received by every destination node or router divided by the scenario run time.

17/10/2003TCP performance over ad-hoc mobile networks. 14 Simulation methodology (cont). Throughput Calculation(in details) The generated tcl files (scenarios) produce traces file during their run. The relevant lines, in trace file,consist in their first column “r” (received), in the seventh “tcp” and In the eighth column the size of the TCP packet in bytes.

17/10/2003TCP performance over ad-hoc mobile networks. 15 Simulation Results In the following slides each graph has the same environment Configurations. The changes are in the TCP configurations on TCP NewReno. The TCP configurations are: BASE: Basic configuration. SACK: Selective acknowledgment and delayed Ack. LT: Limited transmit. ECN: Explicit congestion notification. Note: Not all routing protocols in the ns support the ECN option.

17/10/2003TCP performance over ad-hoc mobile networks. 16 Dynamic Source Routing

17/10/2003TCP performance over ad-hoc mobile networks. 17 Configurations Environment configurations: area size 500m*400m, total nodes, 25 and one source In this configuration there is no significant difference in the throughput. The reason for that is when one source node transmits, no series congestion can be produced.

17/10/2003TCP performance over ad-hoc mobile networks. 18 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 19 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 20 Configurations Environment configurations: area size 500m*400m, total nodes 25, 10 sources. In this configuration we are witnessing to the greater impact sack has to the throughput performance impact. Limited transmit does not improve TCP performance.

17/10/2003TCP performance over ad-hoc mobile networks. 21 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 22 Graphs (cont).

17/10/2003TCP performance over ad-hoc mobile networks. 23 Graphs (cont). As can seen in the following graph, SACK has a greater impact over high velocities.

17/10/2003TCP performance over ad-hoc mobile networks. 24 Configurations Environment configurations: area size 1500m*1000m, total nodes 25, 10 sources. Throughput in general has increased due to the area size changes.

17/10/2003TCP performance over ad-hoc mobile networks. 25 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 26 Graphs (cont). A Comparison between throughput improvements over two area sizes – 500m*400m and 1500m*1000m, both with 10 sources out of total 25 nodes.

17/10/2003TCP performance over ad-hoc mobile networks. 27 Destination Sequenced Distance Vector

17/10/2003TCP performance over ad-hoc mobile networks. 28 Configurations Environment configurations: area size 600m*400m, total nodes 11, 6 sources.

17/10/2003TCP performance over ad-hoc mobile networks. 29 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 30 Graphs (cont). nodes Throughput average improvement comparison over DSDV.

17/10/2003TCP performance over ad-hoc mobile networks. 31 Ad-hoc On-demand Distance Vector

17/10/2003TCP performance over ad-hoc mobile networks. 32 Configurations Environment configurations: area size 600m*400m, total nodes 11, 6 sources.

17/10/2003TCP performance over ad-hoc mobile networks. 33 Graphs

17/10/2003TCP performance over ad-hoc mobile networks. 34 SACK improvement comparison. Graphs - SACK improvement over different routing protocols. All with the same topology: 600m*400m, 6 sources out of total 11 nodes.

17/10/2003TCP performance over ad-hoc mobile networks. 35 SACK improvement comparison. Graphs (cont). Notice the SACK improvement over DSR routing protocol in compare to the improvement over other routing protocols

17/10/2003TCP performance over ad-hoc mobile networks. 36 Temporally Ordered Routing Algorithm

17/10/2003TCP performance over ad-hoc mobile networks. 37 TORA Problematic Character The run results shows that this routing protocol performance is highly sensitive to topology. Therefore conclusive conclusions could not be made regarding TCP performance using this routing protocol. The following graph demonstrates the performance sensitivity to topology in TORA routing protocol.

17/10/2003TCP performance over ad-hoc mobile networks. 38 TORA Problematic Character. Graph mx1000m, 25 nodes, 10 sources.

17/10/2003TCP performance over ad-hoc mobile networks. 39 Conclusions

17/10/2003TCP performance over ad-hoc mobile networks. 40 Selective ACK conclusions The selective ACK showed the best TCP performance improvement. Its performance out-goes over all routing protocols and topologies that were examined in this project. In ad-hoc mobile networks there is a high probability for packets loss due to high bit error rate, and frequent topology changes. SACK is mainly helpful during multi packets loss in the same sending window. SACK had shown up to 12% performance improvement while using high velocities. In high velocities frequent topology changes occur which causes more packets loss.

17/10/2003TCP performance over ad-hoc mobile networks. 41 Limited Transmit conclusions Limited transmit had poorly throughput performance in our research (similar to base and some times even lower). It ’ s happened because LT nature is quite aggressive which may contribute to creation of fast congestion. Studies has shown that LT is more effective when the duration of the connection is short (browser use http 1.0) because the sender can not probe the bandwidth due to small amount of data to be sent, and we used long and heavy connections (FTP).

17/10/2003TCP performance over ad-hoc mobile networks. 42 Explicit Congestion Notification conclusions During our work on the project we have run enormous scenarios and no a real improvement using ECN was viewed. There are some reasons that could cause to that situation: RED is strong enough for signaling the sources for congestion and therefore ECN can not contribute dramatically.

17/10/2003TCP performance over ad-hoc mobile networks. 43 Explicit Congestion Notification conclusions (cont). A quite high loss packets environment as in the ad hoc mobile network causes loss of TCP ACK packets with the ECN field set which reduce the power of ECN. RED seems to be difficult to tune, and adding ECN to RED in mobile ad hoc networks were the topology is very dynamic make it more difficult to use it in an optimal manner (we tried to tuned RED queue parameters and still no significant result).

17/10/2003TCP performance over ad-hoc mobile networks. 44 Topology Size conclusions. As seen on run results, the throughput depends on network dimensions. On the contrary to our first assumption the throughput increased when network dimensions grew, however the throughput behavior is not linear