In this paper we study the Optical Burst Switching (OBS) paradigm for the support of the TCP flows in an All Optical Network (AON). We analyze the TCP send rate, i.e. the amount of data sent per time unit, taking into account of: i) the burst assembly mechanism, called burstification process; ii) the burst loss events inside the OBS network. The goals of the paper are to investigate the effect of the variation of the burstification period and to derive some general guidelines about the dimensioning of the burstification period. With respect to the case in which any assembly mechanism is missing, the results show that an accurate dimensioning of the burstification period yields negligible penalties with regard to the low speed sources and significant benefits with regard to the high speed sources.