在OPNET模型中，当包被传送到发送器请求发送后，实际中的情况是 包将立即被发送到通信信道上进行传输，因此OPNET必须对通信信道进行建模，也就是在模型中要实现物理层的特征，以便将信道对包产生的传输效果考虑进整个网络模型。OPNET将信道对包产生的传输效果建模为若干个计算阶段（称为pipeline stage），最终来判断该包能否被接收到。 -In the OPNET model, when the packet sent to the transmitter sends a request, the actual situation in the package will be immediately sent to the communication channel for transmission, so OPNET to model the communication channel, which is to be achieved in the model physical layer characteristics, in order to channel the transmission of packets have the effect to take into account the entire network model. OPNET will channel the effect of the transmission packet generation model calculation for the number of stages (called pipeline stage), finally to determine whether the packet was received.