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We study the performance of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end rate estimation in a way that is totally transparent to routers and to the destination. Thus, it is compatible with any network and TCP implementation. The key innovative idea is to continuously estimate, at the TCP sender, the packet rate of the connection by monitoring the ACK reception rate. The estimated connection rate is then used to compute congestion window and slow start threshold settings after a congestion episode. Resetting the window to match available bandwidth makes TCPW more robust to sporadic losses due to wireless channel problems. These often cause conventional TCP to overreact, leading to unnecessary window reduction. Experimental studies of TCPW show significant improvements in throughput performance over Reno and SACK, particularly in mixed wired/wireless networks over high-speed links. The contributions of this paper include a model for fair and friendly sharing of the bottleneck link and a Markov Chain performance model in presence of link errors/loss. TCPW performance is compared to that of TCP Reno, and analytic results are validated against simulation results. Internet and laboratory measurements using a Linux TCPW implementation are also reported, providing further evidence of the gains achievable via TCPW.

In a smart city environment, we look at a new, upcoming generation of vehicles running on electric power supplied by on-board batteries. Best recharging options include charging at home, as well as charging at public areas. In this setting, electric vehicles will be informed about public charging stations using wireless communications. As the charging stations are shared resources, cooperating electric vehicles have the potential to avoid unbalanced use of recharging stations and lengthy waiting times.We present a model for electric vehicles and their battery depletion, vehicle mobility, charging stations, and give a solution for optimal placement of charging stations in a smart city. Our placement approach is based on genetic programming and simulation of electric vehicles which move on a real map of a European city. We show that after a few evolution steps, an optimal solution of the charging infrastructure is derived based on mean trip times of electric vehicles.

We consider a system where users aboard communication-enabled vehicles are interested in downloading different contents from Internet-based servers. This scenario captures many of the infotainment services that vehicular communication is envisioned to enable, including news reporting, navigation maps and software updating, or multimedia file downloading. In this paper, we outline the performance limits of such a vehicular content downloading system by modelling the downloading process as an optimization problem, and maximizing the overall system throughput. Our approach allows us to investigate the impact of different factors, such as the roadside infrastructure deployment, the vehicle-to-vehicle relaying, and the penetration rate of the communication technology, even in presence of large instances of the problem. Results highlight the existence of two operational regimes at different penetration rates and the importance of an efficient, yet 2-hop constrained, vehicleto-vehicle relaying.

ttb.urflcr-In ibis pqw, we outllnc a nictliodology that can lie applied lo rirodel the hehilvior of TCP h w s . The proposed trethodology stcins frunr B Mnrltuvinii model of n single TUP source, nnd cvcntriully coiisidcis the su. pci~osition aiid iiitcracllon uf scvcrnl such suiircccs rising stniitlanl qiicucirrg aiialysk twhniqtlu. Oiir approncli nllows thc evaluntion o f such perforiiiincc indica m tliraughpiit, qiieiiclng 11cli1y mil pnckct lws of TCP flows. 'I'he restilts obtained through ~U F mndcl are vnlidnted by iiieaiis of s1111uIa-liuii, under several topology nnd trnftic settings. I . INTKODUC'l'IONAccording to recent estitiintcs 95% of the h-aliic c;trriecl toclay over widc-arm 11' iictworks uses TCP as transpo1.t protocol, which ainouiils to 80% of tlic ovcrall end-lo-cnd flow count. These figures alonc highlight the key rnle that 'I'CP plays in delivering a rcliable servicc tu the most comnioii iicrwork applications such as ernail programs and Web browsers. Diiring the innny years of "Iionorablc" scrvice, TCP tias undergono scvcral alI.clations that Iiave in& it mol-c robust lo cliangitrg traffic patteri~s and to nctwtirk cimgcstion. However, the rcsulliiig co~riplexity OT the algoIittims governing TCP's flow control dynaiiiics has so fiir dcficd any nccuralc analylic mprcsontation.In recent years, several clrwts havc bceii dcvoted to modcliitg such a coinplcx protocol as TCP. Some papers Iiwc tricd to capture the essential TCP dynamics through closed-form exprcssions. Lakshman and Madhow [ l ] and Kumar [Z] use Markovian analysis to dcvclnp il closcil-form expression for the tl~rc~ughput or TCP connections by observing thc cyclical cvolution ofthc TCP transmissiori window; lhc latter work introduces sonic c.xtcnsioiis h r scvcral vcrsioris of X P , incorpor;iting such features EIS coarse timers, fast rctransmit and has1 recovcry. A fluid rnotlcl o f i i single TCP coniicction sharing a link with bmkgruuiid, noii-'I'CP traffic was proposed by hltman ct al. 131 in R tiyhrid approach combining both analytical and cxpcrimenta1 work; a q was done in other, inme recent studies, their modcl proceeds tbmugb a stochastic aiirilysis of the dynamic behavior of 1'ClP's congcstion window sixe: specifically, they aim at PTOviding aa cxprcssion for the throughput nf a single crmnechn. Similarly, Mathis et til. [4j fncusctl on ttie stochastic bchavior of tlic Congestion Avoidancc mcchatiism, deriving an cxpression for thc. ttiroiighput that was tlrcn npplietl to study tlic behavior scvcml flavors of ' K P so~irccs and qucucing tcctiniqucs. Rcccritly, Padhye et al. I S ] havc devdopccl a steady-state niodd rhnc appmximatcs the thronghpiit of bulk TCF jlows as R fiinction of loss rate nnrl round trip lime, coinparring their estiinales witli rc.nl-lifc traccs of ' K P tml'lic. Notably, smnc rescnrclicrs [GI, 1:7] have chosen a different ap-.I ills work \VIIS ruplJorietl by ithe ~mlinti Miiiisrry for Universiiy xitl SciciitificI