Lighttpd

I have use lighttpd 1.4.59 for proxy streaming using live555 http tunnel.

Proxy configuration in lighttpd.conf:

$HTTP["url"] =~ "(^/stream1$)" {
        proxy.server  = ( "" => ("" => ( "host" => "127.0.0.1", "port" => "9037" )))
        server.stream-request-body  = 2
        server.stream-response-body = 2
        server.protocol-http11 = "disable" 
}

Basically streaming client(vlc) get packet from lighttpd 80 port and lighttpd get packet from live555 9037 tunnel server. Apart from this we have configured rtsp session keepalive timeout 60 seconds means if live555 does not get OPTION packet from client within 60 second then it will disconnect client and stream will stop.

issue :
Once we start streaming, live555 continually get keepalive packet from client via lighttpd proxy within 60 seconds but after around 3 hour somehow it is not getting keepalive packet and due to that live555 disconnect client.

observation :
We have conformed that client is sending keepalive packet to lighttpd 80 port but somehow lighttpd proxy not able to send keepalive packet live555 tunnel.

Query :
Why lighttpd stop sending keepalive packet to live555 tunnel?