Patent ID: 8386783
Filing Date: 2013-02-26
Classification: H04L

Abstract:
1. A communication system comprising: an internal host device that is connected to an internal network connected to an external network through a firewall that blocks communications from the external network and selectively allows the communications to the external network and includes a first establishing and maintaining unit and a service call unit; and an external host device that is connected to the external network and includes a second establishing and maintaining unit and a service call receiving unit, wherein: the first establishing and maintaining unit transmits a communication session establishment request to the external host device, and determines that the communication session that communicates to the internal host device from the external host device has been established when the response received from the second establishing and maintaining unit is a communication session maintenance response; the second establishing and maintaining unit transmits the communication session maintenance response to the first establishing and maintaining unit on the basis of the communication session establishment request received from the first establishing and maintaining unit, and constantly transmits a channel maintenance response to the first establishing and maintaining unit in appropriate timing to maintain the communication session; the service call receiving unit identifies a service received from an another device in the external network on the basis of a call of the service, and transmits a service call request that includes a call identification number for identifying the call to the first establishing and maintaining unit through the communication session from the second establishing and maintaining unit; the first establishing and maintaining unit maintains the communication session without cutting off the communication session when the response received from the second establishing and maintaining unit is the channel maintenance response, and calls a service in the internal network according to the service call request received from the service call receiving unit by the service call unit and transmits the response to the call of the service and the call identification number to the external host device through another channel different from the communication session when the response received from the second establishing and maintaining unit is the service call response if it is determined that the communication session has been established; the service call receiving unit identifies the device of the call origin that has called the service on the basis of the call identification number received from the service call unit through the another channel, and transfers the response received from the service call unit through the another channel to the identified device.