TCP/IP over the Bluetooth Wireless Ad-hoc Network Niklas Johansson, Maria Kihl and Ulf Korner Department of Communication Systems, Lund University, Sweden (niklasj, maria, ulfk)@telecom.lth.se Abstract. Bluetooth is a wireless ad-hoc network concept that was presented in February 1998 by its five original promoters Ericsson, Nokia, IBM, Toshiba and Intel. With Bluetooth, mobile terminals within range of each other can set up ad- hoc connections for both synchronous traffic, e.g. voice, and asynchronous traf- fic, e.g. IP-based data traffic. In this paper we analyse how well Bluetooth can carry TCP/IP traffic and in particular we show that though the radio channel is very disturbed the TCP Vegas protocol with its flow control mechanism can be carried very well. With ARQ handled at the Bluetooth level, retransmissions are made immediately after a packet error and thus the delays, normally introduced are kept acceptably short. In our model important mechanisms in TCP Vegas as well as Bluetooth mechanisms are modelled in detail and we show that TCP throughput is quite high and delays are kept short for packet error probabilities up to 50% and moderate loads. 1. Introduction Bluetooth is a wireless ad-hoc network concept that was presented in February 1998. With Bluetooth, mobile terminals within range of each other can set up ad-hoc connec- tions. It is designed for both synchronous traffic, e.g. voice, and asynchronous traffic, e.g. IP-based data traffic. The Bluetooth Special Interest Group (SIG), led by a nine- company Promoter group including 3Com, Ericsson, IBM, Intel, Lucent Technologies, Microsoft, Motorola, Nokia and Toshiba, is driving development of the technology and bringing it to market. For more information, see [4]. Wireless ad-hoc networks have been examined in some papers. The research has mostly been focused on routing (see, for example, Johnson [21]). Perkins [22] exam- ined how mobile-IP could be used in ad-hoc networks. Davies et al. [23] suggested that token passing should be used in the MAC protocols for wireless LANs. However, only a few papers have examined Bluetooth. Haartsen [5] gives a good introduction to the technology used in Bluetooth (see also the Bluetooth Specification ver. 1.0 [6]). Johansson et al. [1][2][3] presents and examines a number of different network usage cases for Bluetooth. In order to achieve good network performance, ad-hoc networks must ensure relia- ble data transfer for the applications. Therefore, the data packets in Bluetooth are pro- tected by an ARQ scheme on the link layer. However, it is also necessary to have good end-to-end congestion control. The obvious solution is to use the Transmission Control Protocol (TCP), that guarantees reliable, in-sequence delivery of packets (see, for example, Stevens [10]). The congestion control in TCP uses a dynamic sliding window to control the rate at which packets are transmitted. The congestion control scheme in TCP was first devel- oped by Jacobson [9]. The most used version right now is called TCP Reno (see, for G. Pujolle et al. (Eds.): NETWORKING 2000, LNCS 1815, pp. 799-810, 2000. © Springer-Verlag Berlin Heidelberg 2000