Patent ID: 7783700

Claim:
A server apparatus which shares an image to be displayed on a screen with a client terminal, comprising: a frame buffer configured to store the image to be displayed on the screen; an update processing unit configured to update a part of the image in the frame buffer; a sequence number counter configured to generate a sequence number to be given to each of a plurality of packets; a first transmission unit configured to generate a first packet which includes first area information indicating a first area updated in the image, a first image which is an image after update in the first area, and a sequence number assigned by the sequence number counter, and to transmit the first packet to the client terminal; a transmission history storage unit configured to store a set of the first area information and the sequence number; a retransmission request reception unit configured to receive a retransmission request including a sequence number from the client terminal; a retransmission image generation unit configured to detect a second area which has not been updated in the first image corresponding to the sequence number included in the retransmission request after the first image was transmitted by referring to the transmission history storage unit and to acquire a second image in the second area from the frame buffer; and a second transmission unit configured to generate a second packet including second area information indicating the second area, the second image, and a sequence number assigned from the sequence number counter, to transmit the second packet to the client terminal and to request the transmission history storage unit to store a set of the second area information and same sequence number as that included in the second packet.