A method for establishing a communication session between a first communication client located within a first communication network, and a second communication client, via a signaling server located within a second communication network distinct from the first communication network and connected thereto via a address translation device. The method includes the step of binding a first address and a second address of the first communication client within the address translation device, by having the first communication client transmit registration messages according to the UDP protocol to the communication server. The method further includes saving, at the communication server, an incoming signaling message sent from the second communication client and intended for the first communication client; replying, by the communication server, to the registration message of the first communication client that follows with a reply message requesting that the first communication client send a new registration message using the TCP protocol; and delivering, by the communication server, the incoming signaling message after the new registration message using the TCP protocol has been received from the first communication client.