184.108.40.206.2 Empty Sync Response
The server sends a Sync response (section 220.127.116.11) with only HTTP headers, and no XML payload, if there are no pending server changes to report to the client. This Sync response is referred to as an empty Sync response. The client can respond to the empty Sync response with an empty Sync request if there are no pending client changes and if the client is required to conserve bandwidth; otherwise, a Sync request with an XML payload can be sent. For more information about empty Sync requests, see section 18.104.22.168.1. For an example of an empty Sync request and response, see section 4.5.10.