In this paper, we investigate the consensus problem over the communication network where the communication channels are represented by LTI systems. We give the necessary and sufficient conditions for solving consensus problems under two different architectures. The consensus value in our framework proved to be only related with the network topology and communication channel characteristics. We further assume that the communication channels are not well known but belong to some uncertainty class. We give a sufficitent condition to reach consensus by which we only need to know the DC gain of each channel and the bound of its H-infinity norm. We also establish a bound for the H-infinity norm of the channel dynamic vectors to ensure the stability of the network and show this bound is a conservative one compared with the bound required for consensus.