A communication system includes a first endpoint located behind a first connectivity barrier, such as a firewall or a consumer gateway, and a second endpoint. A service is arranged to respond to a request from the first endpoint to establish communications with the second endpoint by assigning a server to handle a session between the first endpoint and the service. A session initiated by the second endpoint is established with the service if the second endpoint is located behind a second connectivity barrier. If the second endpoint is not located behind a connectivity barrier, a transport level communications connection can be established with the second endpoint. In some cases, the service can instruct the first endpoint to establish a direct session with the second endpoint.