Prashant,

H.323v5 and later provides some insight (section 8.2.1):

When tunnelling is active, one or more H.245 messages can be encapsulated in any H.225.0 call signalling message. If tunnelling is being utilized and there is no need for transmission of a H.225.0 call signalling message at the time an H.245 message must be transmitted, then a Facility message shall be sent with the reason set to transportedInformation. (Note that H.323 systems prior to version 4 used a Facility message with h323 message body set to empty.)

It might be used for either H.245 tunneling or for supplementary services (H.450-series) messages, or for non-call-related messages.  You will see both empty and Facility employed, but newer devices should switch to using Facility for H.245 tunneling.

Paul

From: prashant patel [mailto:prashantitpatel@rediffmail.com]
Sent: Thursday, April 30, 2009 6:15 AM
To: h323forum@mail.imtc.org; h323plus@lists.packetizer.com
Subject: [h323plus] Difference b/w FACILITY and EMPTY messages

Hi All,
I would like to know the difference between FACILITY and EMPTY message. While doing TUNNELING I am getting OLC body through EMPTY header(H225).
Can I use FACILITY method instead of EMPTY.

Thanks,
Prashant