The evolution of transport protocols: An evolutionary game perspective Eitan Altman a, * , Rachid El-Azouzi b , Yezekael Hayel b , Hamidou Tembine b a INRIA, Centre Sophia-Antipolis, 2004 Route des Lucioles, 06902 Sophia-Antipolis Cedex, France b University of Avignon, LIA/CERI, 339, Chemin des Meinajaries, Agroparc BP 1228, 84911 Avignon Cedex 9, France article info Article history: Received 12 December 2007 Received in revised form 11 September 2008 Accepted 16 December 2008 Available online xxxx Keywords: Evolutionary games TCP Protocols Replicator dynamics abstract Today’s Internet is well adapted to the evolution of protocols at various network layers. Much of the intelligence of congestion control is delegated to the end users and they have a large amount of freedom in the choice of the protocols they use. In the absence of a cen- tralized policy for a global deployment of a unique protocol to perform a given task, the Internet experiences a competitive evolution between various versions of protocols. The evolution manifests itself through the upgrading of existing protocols, abandonment of some protocols and appearance of new ones. We highlight in this paper the modeling capa- bilities of the evolutionary game paradigm for explaining past evolution and predicting the future one. In particular, using this paradigm we derive conditions under which (i) a suc- cessful protocol would dominate and wipe away other protocols, or (ii) various competing protocols could coexist. In the latter case we also predict the share of users that would use each of the protocols. We further use evolutionary games to propose guidelines for upgrad- ing protocols in order to achieve desirable stability behavior of the system. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction When transferring data between nodes, flow control protocols are needed to regulate the transmission rates so as to adapt to the available resources. A connection that looses data units has to retransmit them later. In the ab- sence of adaptation to the congestion, the on going trans- missions along with the retransmissions can cause increased congestion in the network resulting in losses and further retransmissions by this and/or by other con- nections. This type of phenomenon, that had lead to sev- eral ‘congestion collapses’ [15], motivated the evolution of the Internet transport protocol, TCP, to a protocol that reduces dramatically the connection’s throughput upon congestion detection. The possibilities to deploy freely new versions of proto- cols on terminals connected to the Internet creates a com- petition environment between protocols. Much work has been devoted to analyze such competition and to predict its consequences. The two main approaches for predicting whether one version of a protocol would dominate another one are  Inter-Population Competition (IRPC): One examines local interactions between connections of different types that interact with each other (by sharing some common bot- tleneck link). If a connection that corresponds to one version performs better in such an interaction, then the IRPC approach predicts that it would dominate and that the other version would vanish.  Intra-Population Competition (IAPC): In this approach one studies the performance of a version of a protocol assum- ing a world where all connections use that version. This is repeated with the other version. One then predicts that the version that gives a better world would dominate. We address the dominance question with the evolu- tionary game paradigm and provide an alternative answer along with a more detailed analysis of this competition scenario. Our approach predicts whether one can expect 1389-1286/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.comnet.2008.12.023 * Corresponding author. Tel.: +33 4 92 38 77 86. E-mail addresses: Eitan.Altman@sophia.inria.fr (E. Altman), Rachid. Elazouzi@univ-avignon.fr (R. El-Azouzi), Yezekael.Hayel@univ-avignon.fr (Y. Hayel), Hamidou.Tembine@univ-avignon.fr (H. Tembine). URL: http://www-sop.inria.fr/maestro/personnel/Eitan.Altman/ (E. Altman). Computer Networks xxx (2009) xxx–xxx Contents lists available at ScienceDirect Computer Networks journal homepage: www.elsevier.com/locate/comnet ARTICLE IN PRESS Please cite this article in press as: E. Altman et al., The evolution of transport protocols: An evolutionary game perspective, Comput. Netw. (2009), doi:10.1016/j.comnet.2008.12.023