Communication apparatus and control method thereof and communication system

A communication system comprising:

• an imaging apparatus including a first communication unit;
• and a terminal apparatus including a second communication unit,
• wherein the imaging apparatus functions as a server by using a request/response communication protocol with the first communication unit,
• wherein the terminal apparatus functions as a client by using a request/response communication protocol with the second communication unit,
• wherein the terminal apparatus includes:
• a first processing unit that sends a predetermined polling request to the imaging apparatus, and displays a menu of a plurality of processing items for the imaging apparatus;
• a second processing unit that, when one of the processing items of the menu is selected by a user before a response to the predetermined polling request is received from the imaging apparatus, sends a request for the selected processing item to the imaging apparatus, receives a cancellation response to the predetermined polling request, and thereafter shifts to processing corresponding to the request for the selected processing item;
• and
• a third processing unit that, when a response to the predetermined polling request is received from the imaging apparatus without any one of the processing items of the menu being selected by the user, shifts to processing for acquiring an image described in the response,
• wherein the imaging apparatus includes:
• a fourth processing unit that displays, when the predetermined polling request is received from the terminal apparatus during communication with the terminal apparatus, a list of imaged images stored in the imaging apparatus so as to be selectable by the user, accepts selection of an image by the user, and sends, when a sending instruction is input from the user, information specifying the selected image to the terminal apparatus as a response to the predetermined polling request;
• and
• a fifth processing unit that sends, when another request is received from the terminal apparatus before a response to the predetermined polling request is sent to the terminal apparatus by the fourth processing unit, a cancellation response to the predetermined polling request, and performs processing corresponding to the other request.