| 摘要 |
A subnetwork of client computers includes a designated relay host computer that communicates through a firewall with an outside server computer located within the same computing environment or over an Internet connection. A specially-designated URL on the server is used when the relay host requests that a downlink connection be kept alive indefinitely with the server computer. The server receives the HTTP request and activates a continuous heartbeat program. Heartbeat messages are sent continuously from the server computer to the relay host to keep the downlink connection open indefinitely. When the server needs to send an urgent message to the client computers it can do so immediately by using the already open downlink connection. The relay host forwards messages to the other component client computers in the subnetwork. The relay host may also use a proxy server. The downlink connection uses a standard request-reply protocol.
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