In a high-speed lightwave system, chirping of transmitters as well as dispersion and nonlinearity of the fiber distort the transmitted pulse. Moreover, the frequency characteristics of receivers have an important impact on the intersymbol interference at the input of the decision circuit. Therefore, it is necessary to use appropriate model of chirping of transmitters and frequency characteristics of receivers in order to estimate transmission performance accurately. Chirping of Mach-Zehnder type LiNbO3 based transmitters can be modeled by two methods. The receiver sensitivity made a difference of at least 1-2 dB by the receiver filter model and shape of chirping. The measured receiver filter provided closer results to the experimental results and BER characteristics provided more accurate system performances, especially by using chirping model 1 for negative chirp and chirping model 2 for positive chirp.