To meet various contingencies of operating wireless networks such as the change of the state of a channel, cross-layer techniques facilitate sharing of information between OSI model layers. These techniques can be apply to various protocols levels, if there are interactions for which the overall performance of the system under studies can be improved. Reliable transport protocols use the exponential back-off mechanism when a bad state of the wireless channel occurs, which temporarily blocks the transmission of data. In this paper, we suggest a new policy of timeout applied to the SCTP protocol called persistent timeout policy. This policy is based on the use of the channel status provided by the 802.11 link layer, through the cross-layer mechanism. The principle of this timeout is that when a bad state of the wireless channel blocks the sending of data, SCTP continuously observes the evolution of this state to detect the next favourable change before sending its segments. We evaluate the following two timeout policies (persistent and exponential back-off) of the SCTP protocol in an ad hoc network, and in comparison also with TCP. Section I of this paper presents an overview of the SCTP protocol. Section II presents the principle of the persistent timeout policy. Section III presents the simulation results that are used to compare the two timeout policies of the two reliable transport protocols SCTP and TCP.
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