A study of TCP performance in wired cum ad hoc environments

A STUDY OF TCP PERFORMANCE IN WIRED-CUM-AD HOC ENVIRONMENTS YANG LUQING (B ENG., NUPT, P R CHINA) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2003 Acknowledgements I would like to express my deep and sincere gratitude to Dr Winston Seah, who guides me all the way to the ad hoc network world, and sparks this research with his constant help, tremendous efforts, and precious enlightenment I am also cordially grateful to Dr Yin Qinghe, who always gives me valuable inspirations and helpful suggestions during our discussions It is a great pleasure to have them as my supervisors, and to work with them together I also thank NUS and I2R for providing me with this opportunity to pursue my M.Eng study here So many friends in NUS and I2R help me both in my research and in my life here, especially I would like to acknowledge the assistance of Mr Li Feng and Mr Teh Keng Hoe Finally, special thanks must go to my wife and my parents, who support me with their love and encourage me to my best in life I Contents SUMMARY IV ABBREVIATIONS .VI LIST OF FIGURES VII LIST OF TABLES IX CHAPTER INTRODUCTION 1.1 OVERVIEW OF AD HOC NETWORKS 1.2 OVERVIEW OF TCP PERFORMANCE IN AD HOC NETWORKS 1.3 THESIS CONTRIBUTIONS 1.4 THESIS ORGANIZATION CHAPTER LITERATURE REVIEW 2.1 INTRODUCTION 2.2 PROPOSED TCP ALGORITHMS 2.3 TCP PERFORMANCE IN AD HOC NETWORKS 10 2.3.1 Improving TCP Performance in MANET 10 2.3.2 TCP Interactions with Lower Layer Protocols 11 2.4 SUMMARY 13 CHAPTER EVALUATION OF TCP ALGORITHMS IN WIRED-CUM-AD HOC ENVIRONMENTS 14 3.1 INTRODUCTION 14 3.2 SIMULATION CONFIGURATION 14 3.3 SIMULATION RESULTS AND DISCUSSIONS 15 II 3.3.1 Static Scenario without Congestion 16 3.3.2 Static Scenario with Congestion 23 3.3.3 Scenario with Node Mobility 28 3.3.4 Impact of Rerouting on Vegas Performance 33 3.3.5 Conclusions of Evaluation Results 37 3.4 SUMMARY 38 CHAPTER IMPROVING FAIRNESS BETWEEN TCP FLOWS IN WIREDCUM-AD HOC ENVIRONMENTS 39 4.1 INTRODUCTION 39 4.2 PROBLEM IDENTIFICATION 39 4.3 DESIGN OF THE SCHEME 41 4.4 SIMULATION RESULTS 43 4.4.1 Simulation Environment 43 4.4.2 Simulation Results 45 4.5 ANALYSIS AND DISCUSSIONS 55 4.6 LIMITATION OF OUR APPROACH AND FUTURE WORK 57 4.7 SUMMARY 58 CHAPTER CONCLUSIONS AND FUTURE WORK 59 5.1 CONCLUSIONS 59 5.2 FUTURE WORK 60 PUBLICATION LIST 62 REFERENCES 63 III Summary With the rapid advancement in mobile computing devices and wireless communication technology, the demand for continuous network connectivity regardless of physical location has spurred interest of the use of ad hoc networks, which are instantly deployable and find their applications in disaster rescue, battlefield, and many other scenarios Ad hoc networks may operate in a standalone fashion, or may be connected to wired networks, such as the Internet Actually many foreseeable applications of ad hoc networks require connections to be established between wired network and wireless ad hoc network for various purposes, such as Internet surfing, database update, etc We call this kind of connection patterns wired-cum-ad hoc networks As the de facto transport protocol in the Internet, TCP, is sure to be used over ad hoc networks Many researchers have studied TCP performance in ad hoc networks that operate in a standalone fashion However, few researches have been done to investigate TCP performance in wired-cum-ad hoc environments, which motivates us to conduct this research This thesis provides an in-depth study on TCP performance in wired-cum-ad hoc networks Two important properties of TCP, throughput and fairness, are both addressed First, a comprehensive evaluation of different TCP algorithms performance in wired-cum-ad hoc environments is done, and the results give clear answers to questions like which TCP algorithm should be implemented in this specific scenario, and how to tune TCP parameters to optimize its performance Moreover, this thesis also presents a scheme that successfully eliminates the severe unfairness between TCP IV flows spanning wired and IEEE802.11-based wireless ad hoc networks Simulation results show that our scheme improves the fairness between TCP flows greatly without incurring much throughput loss V Abbreviations ACK AODV ARP BER CBR CTS cwnd DSDV DSR ECN ELFN FIFO FTP ICMP IETF MAC MANET maxcwnd NS RFC RTO RTS RTT SSA SACK ssthresh TCP UDP TCP Acknowledgement Ad hoc On-demand Distance-Vector routing protocol Address Resolution Protocol Bit Error Rate Constant Bit Rate Clear To Send Congestion Window Dynamic Destination-Sequenced Distance Vector routing Dynamic Source Routing Explicit Congestion Notification Explicit Link Failure Notification First In First Out File Transfer Protocol Internet Control Message Protocol Internet Engineering Task Force Media Access Control Mobile Ad hoc NETwork Maximum congestion window size Network Simulator Request For Comments Retransmission TimeOut Request To Send Round Trip Time Signal Stability based Adaptive routing TCP Selective Acknowledgement TCP Slow Start Threshold Transmission Control Protocol User Datagram Protocol VI List of Figures Figure 3.1 The static scenario without wired cross traffic 16 Figure 3.2 MAC layer trace of TCP and IEEE 802.11 interaction 19 Figure 3.3 Static scenario with congestion on wired links 23 Figure 3.4 TCP goodput (kb/s), CBR = 1.6 Mb/s, Exp = 0.4 Mb/s 25 Figure 3.5 TCP goodput (kb/s), CBR = 1.5 Mb/s, Exp = 0.4 Mb/s 26 Figure 3.6 Scenario for mobility impact study 29 Figure 3.7 TCP performance in mobile environments 30 Figure 3.8 Scenario for studying rerouting impact on Vegas 34 Figure 3.9 Rerouting impact on Vegas (Goodput: Kb/s) 35 Figure 3.10 Congestion window size comparison 36 Figure 4.1 Testbed for identification of unfairness 40 Figure 4.2 Scenario A for simulation 43 Figure 4.3 Goodput of normal scheme, wired link delay = 5ms 46 Figure 4.4 Goodput of our scheme, wired link delay = 5ms 46 Figure 4.5 Maxcwnd = 4, wired link delay = 5ms, normal scheme 47 Figure 4.6 Maxcwnd = 4, wired link delay = 5ms, our scheme 47 Figure 4.7 Maxcwnd = 8, wired link delay = 5ms, normal scheme 48 Figure 4.8 Maxcwnd = 8, wired link delay = 5ms, our scheme 48 Figure 4.9 Goodput of normal scheme, wired link delay = 45ms 49 Figure 4.10 Goodput of our scheme, wired link delay = 45ms 50 Figure 4.11 Scenario B for simulation 51 Figure 4.12 Goodput of normal scheme for scenario B 51 Figure 4.13 Goodput of our scheme for scenario B 52 VII Figure 4.14 Maxcwnd = 8, normal scheme for scenario B 53 Figure 4.15 Maxcwnd = 8, our scheme for scenario B 53 Figure 4.16 Pure ad hoc scenario with extreme unfairness 54 Figure 4.17 ACK sequence progress, normal scheme 54 Figure 4.18 ACK sequence progress, our scheme 54 VIII List of Tables Table 3.1 TCP goodput (W0 to node 1, kb/s) 17 Table 3.2 TCP goodput (W0 to node 2, kb/s) 17 Table 3.3 TCP goodput (W0 to node 3, kb/s) 17 Table 3.4 TCP goodput (W0 to node 4, kb/s) 17 Table 3.5 TCP goodput (W0 to node 5, kb/s) 18 Table 4.1 Parameter settings in ns 44 Table 4.2 Parameter settings in our scheme 44 IX Chapter Improving Fairness between TCP Flows Goodput (kb/s) FTP1 800 700 600 500 400 300 200 100 FTP2 SUM 16 TCP maxcwnd Figure 4.13 Goodput of our scheme for scenario B Figure 4.12 gives the results of normal scheme The severe unfairness is shown clearly When maxcwnd is less than 16 packets, FTP2 will stifle FTP1 On the contrary, when maxcwnd is 16 packets, FTP1 will stifle FTP2 It is evident that these two connections cannot coexist well whatever maxcwnd value is used Figure 4.13 shows the results obtained by using our scheme Figure 4.14 and Figure 4.15 present examples of TCP acknowledgement progress Obviously with our scheme the two FTP sessions coordinate well in sharing the channel and they both achieve sustainable throughput It is reasonable that the goodput of FTP2 is more than two times the goodput of FTP1, because FTP2 is a one-hop connection whereas FTP1 crosses two hops in wireless and two hops in wired domain Actually the above-mentioned extreme unfairness not only exists in wired-cum-ad hoc environments, but also exists between TCP connections in pure ad hoc environments 52 Chapter Improving Fairness between TCP Flows 12000 TCP1 TCP2 ACK Sequence Number 10000 8000 6000 4000 2000 0 20 40 Time (s) 60 80 100 Figure 4.14 Maxcwnd = 8, normal scheme for scenario B 6000 ACK Sequence Number 5000 TCP1 TCP2 4000 3000 2000 1000 0 20 40 Time (s) 60 80 100 Figure 4.15 Maxcwnd = 8, our scheme for scenario B Figure 4.16 shows a pure ad hoc scenario Five nodes are evenly spaced with 200 meters away from each other One TCP flow (TCP1) is a two-hop connection from node to node 3, whereas another TCP flow (TCP2) is from node to node Xu and Saadawi [30] have shown that in this scenario, once the one-hop connection starts, the two-hop connection is completely forced down and even cannot get a chance to restart In our simulation, TCP1 starts at second, whereas the one-hop connection TCP2 53 Chapter Improving Fairness between TCP Flows starts at 10.0 second Figure 4.17 and Figure 4.18 show the acknowledgement progress of these two connections node1 node node node node Figure 4.16 Pure ad hoc scenario with extreme unfairness 14000 TCP1 TCP2 ACK Sequence Number 12000 10000 8000 6000 4000 2000 0 20 40 Time (s) 60 80 100 Figure 4.17 ACK sequence progress, normal scheme 6000 TCP1 TCP2 ACK Sequence Number 5000 4000 3000 2000 1000 0 20 40 Time (s) 60 80 100 Figure 4.18 ACK sequence progress, our scheme 54 Chapter Improving Fairness between TCP Flows In Figure 4.17, we can see that the one-hop TCP flow completely stifles the two-hop TCP connection TCP1 does not receive any new acknowledgement after 10.07s in the 100 seconds of simulation Figure 4.18 shows the results obtained by using our scheme, now both flows progress roughly smoothly and coexist well The extreme unfairness once again is eliminated One thing to note is that in the simulation results, the aggregate goodput experiences moderate degradation by using our scheme However, the degradation is acceptable considering the fact that our scheme completely eliminates the extreme unfairness and ensures a sustainable throughput for every TCP connection Moreover, in situations with extreme unfairness, the term aggregate goodput is misleading because it is almost totally contributed by one or few connections with all other TCP connections starved out Considering the situations where ad hoc networks are deployed, such as battlefield and disaster rescue, everyone could foresee the implications of severe unfairness No one will have the desire to implement an ad hoc network if it even cannot ensure every connection a sustainable throughput, let alone fair share, when all links are in good states 4.5 Analysis and Discussions The severe unfairness between TCP flows in IEEE802.11-based wireless ad hoc networks is the result of interactions of TCP, the FIFO work-conserving scheduling scheme, and the IEEE802.11 MAC protocol First, TCP would send packets back-toback when the congestion window allows Moreover, TCP traffic is self-clocking, i.e the faster the acknowledgement comes back, the faster the data packets are sent out Second, IEEE802.11 protocol always favors the node that is successful in the latest contention and leaves the failed nodes in exponential backoff Lastly, work-conserving 55 Chapter Improving Fairness between TCP Flows scheduling helps the last successful node to occupy the channel persistently by always providing packets in time In fact, as long as normal work-conserving scheduling is used with IEEE802.11 MAC protocol, even if other traffic types instead of TCP run on ad hoc networks, the unfairness problem will exist From a different perspective, the packet generation interval of CBR traffic plays a similar role to some extent as the delay we added in scheduling That is the reason why using work-conserving scheduling with CBR traffic usually does not show clear unfairness However, once the CBR load is high, i.e the packet generation interval is small enough, the unfairness will be evident as well Therefore, TCP just exacerbates the unfairness compared with other traffic types By adding extra adaptive delay in scheduling, our scheme successfully eliminates the severe unfairness between TCP flows in wired-cum-ad hoc environments The heuristic behind this design is that by introducing extra adaptive delay we want to only penalize those aggressive nodes to some extent, which grab the channel persistently, and help nodes that fail in the medium contention consecutively to enjoy the resource The faster the node sends out packets, the longer the delay is inserted; the slower the node sends out packets, the shorter the delay is inserted, or even no delay is inserted As described in last chapter, there is fundamental difference between TCP parameter tuning in wired-cum-ad hoc networks and in pure ad hoc networks In pure ad hoc networks, a large congestion window usually does not increase the throughput but worsen fairness However, in wired-cum-ad hoc environments, a small congestion window usually causes unacceptably low throughput Using our scheme, large congestion window is no more a threat to fairness; on the contrary, it contributes to achieving a satisfactory throughput 56 Chapter Improving Fairness between TCP Flows We could foresee that in scenarios where there is only one TCP connection in the network, or each TCP connection always run in disjoint areas without contentions, our scheme would no doubt lead to unnecessary throughput loss However, we argue that those cases are rare and unrealistic in a foreseeable practical wireless ad hoc network 4.6 Limitation of Our Approach and Future Work With further studies, we find that the parameter settings in our approach depend on the number of simultaneous contending sources For example, with the same parameter settings, in some simulation runs the clear unfairness still exists once there are three or more flows contending the service from base station simultaneously, though our approach alleviates it greatly In this situation, to maintain perfect fairness a larger delay value should be inserted Therefore, mathematical analysis needs to be done to decide the quantitative relationship between the delay parameter value and the number of contending sources Actually although the parameter settings in Table 4.2 works well to obtain good fairness, it is set based on our experience and intuition, and we conclude that it may not be the optimal setting without mathematical analysis However, without information from the MAC layer, it is difficult to learn how many sources are contending simultaneously This inspires us to look beyond our current scheme as modifying the scheduling scheme alone is not enough for completely eliminating the unfairness in all scenarios Moreover, we conclude that a new MAC protocol, which integrates the heuristic in our approach with the IEEE802.11 MAC protocol, will work better to eliminate the extreme unfairness in broader circumstances The idea is that the new MAC protocol first determines how many sources are contending simultaneously based on the information it overheard from the air, then every node decides the delay value that should be inserted into the scheduling according to the quantitative relationship between parameter setting and the number of 57 Chapter Improving Fairness between TCP Flows contending sources These ideas have not been addressed in this thesis but serve as future work 4.7 Summary In this chapter, we studied the fairness between TCP flows in wired-cum-ad hoc environments A simple scheme has been presented to eliminate the extreme unfairness existing in this kind of environments Simulation results showed that good fairness could be achieved without incurring much throughput loss by using our approach Meanwhile, we analyzed the limitation of this scheme and gave suggestions of future work We are sure that our work in this chapter would be very helpful in future design of MAC protocol, which is specially designed for multiple hop wireless networks 58 Chapter Conclusions and Future Work 5.1 Conclusions This thesis presents a comprehensive study on TCP performance in wired-cum-ad hoc environments Two important properties of TCP, goodput and fairness, have been addressed We evaluated the performance of four prevalent TCP algorithms, Reno, New Reno, SACK, and Vegas in wired-cum-ad hoc networks The extensive simulation results show that New Reno and SACK are best candidate TCP algorithms for deployment Both these two TCP variants perform robustly in all the scenarios There is no obvious winner between New Reno and SACK Although Vegas outperforms others in several scenarios due to the interactions between its unique proactive congestion control technique and lower layer protocols, Vegas should not be selected for deployment because it cannot always update its notion of base RTT accordingly when rerouting occurs, which may cause Vegas to reduce the congestion window size unnecessarily and lead to significant throughput loss Reno is inferior to New Reno and SACK in its ability to handle the congestion on wired links, which TCP is very likely to face when it spans between ad hoc networks and the Internet Besides finding which TCP algorithm to implement, we analyzed and discussed the impact of TCP parameter tuning We found that RTO rounding up behavior recommended in RFC2988 and TCP minimum RTO setting may have great impact on TCP performance in mobile environments, though the introduction of minimum RTO in RFC2988 is meant to avoid spurious retransmission Our results showed that in 59 Chapter Conclusions and Future Work wired-cum-ad hoc environments, TCP receiver advertised window (or TCP maximum congestion window) should be set to a value as large as the buffer capacity allows, instead of a small value recommended by previous studies on pure ad hoc networks Furthermore, this thesis studied the problem of fairness between TCP flows spanning wired network and wireless ad hoc networks In the literature[2], it has been found that unfairness in this kind of environments is much more severe than that in cellular networks and wireless LAN, the consequence of which often forces one TCP flow to completely stop transferring any data despite all links being in good states No solution has been proposed in the literature In this thesis, we proposed a scheme [4], which helps competing TCP connections to achieve fairness without much throughput loss Simulation results show that our scheme successfully eliminates the extreme unfairness and ensures every TCP connection a sustainable throughput Considering the scenario where ad hoc networks are deployed, such as battlefield and disaster rescue, we argued that a solution to unfairness is as important as proposals of improving TCP throughput We analyzed the limitation of our approach as well, and pointed out a future work direction, which aims to integrate the heuristic in our approach with IEEE802.11 MAC protocol to improve fairness in broader circumstances 5.2 Future Work Throughout our study in this thesis, we strongly feel that TCP performance in wireless ad hoc environments is not only decided by the TCP algorithm itself, but also decided by the interactions among TCP, lower layer routing and MAC protocols However, till now, the routing and MAC protocols are not designed with TCP in mind, which greatly affect the performance when TCP-based applications are running over these protocols On the other hand, most of the time researchers focusing on transport layer 60 Chapter Conclusions and Future Work issues propose TCP improvement schemes without taking the lower layer protocols’ effects into account Therefore, the optimization of routing and MAC protocols to best support TCP applications is a topic deserving future research For example, we think that a MAC protocol that is specially designed to suit the needs of multiple wireless hop environments will greatly improve TCP performance in terms of both throughput and fairness In short, we think that the study of cross-layer interactions and cross-layer protocol design will help improve TCP performance in wired-cum-ad hoc environments 61 Publication List [1] L Yang, Winston K G Seah, and Q Yin, “Improving Fairness among TCP Flows crossing Wireless Ad Hoc and Wired Networks,” in proceedings of ACM MobiHoc’03, pages 57-63, Annapolis, MD, USA, Jun 2003 [2] L Yang, Winston K G Seah, and Q Yin, “TCP Performance Issues in Wiredcum-Ad Hoc Environments,” submitted to IEEE/ACM Transactions on Networking, Oct 2003, file number TNET-00300-2003, in review 62 References [1] IETF Mobile Ad Hoc Network working group charter, Mar 2002, http://www.ietf.org/proceedings/02mar/179.htm [2] K Xu, S Bae, S Lee, and M Gerla, “TCP Behavior across Multihop Wireless Networks and the Wired Internet,” in proceedings of ACM WoWMoM ’02, pages 4148, Atlanta, GA, USA, Sep 2002 [3] L Yang, Winston K G Seah, and Q Yin, “ TCP Performance Issues in Wiredcum-Ad Hoc Environments,” submitted to IEEE/ACM Transactions on Networking, Oct 2003, file number TNET-00300-2003, in review [4] L Yang, Winston K G Seah, and Q Yin, “Improving Fairness among TCP Flows crossing Wireless Ad Hoc and Wired Networks,” in proceedings of ACM MobiHoc’03, pages 57-63, Annapolis, MD, USA, Jun 2003 [5] W Stevens, “TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms,” IETF RFC 2001, Jan 1997 [6] S Floyd, and T Henderson, “The NewReno Modification to TCP's Fast Recovery Algorithm,” IETF RFC2582, Apr 1999 [7] M Mathis, J Mahdavi, S Floyd, and A Romanow “TCP Selective Acknowledgment Options,” IETF RFC 2018, Oct 1996 [8] L Brakmo, and L Peterson, “TCP Vegas, End to End Congestion Avoidance on a Global Internet,” IEEE Journal on Selected Areas in Communications, Vol 13, No 8, pages 1465-1480, Oct 1995 63 References [9] G Holland, and N Vaidya, “Analysis of TCP Performance over Mobile Ad Hoc Networks,” in proceedings of ACM MobiCom ’99, pages 219-230, Seattle, WA, USA, Aug 1999 [10] K Chandran, S Raghunathan, S Venkatesan, and R Prakash, “A Feedback-based Scheme for Improving TCP Performance in Ad Hoc Networks,” IEEE Personal Communications Magazine, pages 34-39, Feb 2001 [11] J Monks, P Sinha, and V Bharghavan, “Limitations of TCP-ELFN for Ad Hoc Networks,” in proceedings of The 7th International Workshop on Mobile Multimedia Communications (MoMuC 2000), Tokyo, Japan, Oct 2000 [12] J Liu, and S Singh, “ATCP: TCP for Mobile Ad Hoc Networks,” IEEE Journal on Selected Areas in Communications, Vol 19, No 7, pages 1300-1315, Jul 2001 [13] K Ramakrishnan, and S Floyd, “A Proposal to add Explicit Congestion Notification (ECN) to IP,” IETF RFC2481, Jan 1999 [14] J Postel, “Internet Control Message Protocol,” IETF RFC792, Sep 1981 [15] F Wang, and Y Zhang, “Improving TCP Performance over Mobile Ad-hoc Networks with Out-of-Order Detection and Response,” in proceedings of ACM MobiHoc’02, pages 217-225, Lausanne, Switzerland, Jun 2002 [16] K Tang, and M Gerla, “Fair sharing of MAC under TCP in wireless ad hoc networks,” in proceedings of IEEE MMT ’99, Venice, Italy, Oct 1999 [17] S Xu, and T Saadawi, “Performance Evaluation of TCP Algorithms in Multi-hop Wireless Packet Networks,” Wireless Communications and Mobile Computing, 2002, No 2, pages 85-100 [18] IEEE Standard 802.11, “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications,” Jun 1999 64 References [19] T Dyer, and R Boppana, “A Comparison of TCP Performance over Three Routing Protocols for Mobile Ad-hoc Networks,” in proceedings of ACM Mobihoc’01, pages 56-66, Long Beach, CA, USA, Oct 2001 [20] A Ahuja, S Agarwal, J Singh, and R Shorey, “Performance of TCP over Different Routing Protocols in Mobile Ad-Hoc Networks,” in proceedings of IEEE VTC’2000, Vol 3, pages 2315-2319, Tokyo, May 2000 [21] C Perkins, and P Bhagwat, “Highly Dynamic Destination-Sequenced DistanceVector Routing (DSDV) for Mobile Computers,” in proceedings of ACM SIGCOMM ’94 Conference on Communications Architectures, Protocols and Applications, pages 234-244, London, UK, Aug 1994 [22] J Broch, D B Johnson, and D A Maltz, “The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks,” Internet-Draft, draft-ietf-manet-dsr-03.txt, Oct 1999 [23] C Perkins, and E Royer, “Ad-hoc On-Demand Distance Vector Routing,” in proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications, pages 90-100, New Orleans, LA, USA, Feb 1999 [24] R Dube, C Rais, K Wang, and S Tripathi, “Signal Stability based Adaptive Routing (SSA) for Ad-Hoc Mobile Networks,” IEEE Personal Communications, Vol 4, No 1, pages 36-45, Feb 1997 [25] Network Simulator, http://www.isi.edu/nsnam/ns/ [26] J Broch, D A Maltz, D B Johnson, Y Hu, and J Jetcheva, “A Performance Comparison of Multi-hop Wireless Ad Hoc Network Routing Protocols,” in proceedings of ACM/IEEE MobiCom ’98, pages 85-97, Dallas, TX, USA, Oct 1998 [27] R Braden, “Requirements for Internet Hosts, Communication Layers,” IETF RFC1122, Oct 1989 65 References [28] V Paxson, and M Allman, “Computing TCP’s Retransmission Timer,” IETF RFC2988, Nov 2000 [29] http://netweb.usc.edu/yaxu/Vegas/Html/vegas.html [30] S Xu, and T Saadawi, “Does the IEEE 802.11 MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks,” IEEE Communications Magazine, Volume 39, Issue 6, pages 130-137, Jun 2001 66 ... that performance evaluation of TCP algorithms must be done both in pure ad hoc environments and in wired- cum- ad hoc environments before choices are made on TCP parameter tuning and which TCP variant... specially focuses on TCP performance study in wired- cum- ad hoc environments 13 Chapter Evaluation of TCP Algorithms in Wired- cum- Ad Hoc Environments 3.1 Introduction As described in Chapter and... accordingly Again, the simulation results reveal the challenges that Reno-based TCP algorithms face in wired- 20 Chapter Evaluation of TCP Algorithms cum- ad hoc environments: A large maxcwnd value will