Why heartbeatTimeout is 3 times as much as heartbeat?

[??]

hi, I'm a little puzzled, why heartbeatTimeout is 3 times as much as heartbeat?


public HeaderExchangeServer(Server server) {
    if (server == null) {
        throw new IllegalArgumentException("server == null");
    }
    this.server = server;
    this.heartbeat = server.getUrl().getParameter(Constants.HEARTBEAT_KEY, 0);
    this.heartbeatTimeout = 
server.getUrl().getParameter(Constants.HEARTBEAT_TIMEOUT_KEY, heartbeat * 3);
    if (heartbeatTimeout < heartbeat * 2) {
        throw new IllegalStateException("heartbeatTimeout < heartbeatInterval * 
2");
    }
    startHeatbeatTimer();
}