[SR-Users] Meaning of empty body in NOTIFY

[Eugen Dedu]

Hi,

ekiga.net registrar uses kamailio 1.5.3 (yes, a bit old...) and for 
users who are not registered an empty NOTIFY body is returned when asked 
by a SUBSCRIBE.  What does this mean from SIP standard point of view, 
and from kamailio point of view (are they identical?)  I see in 
RFC3265/3.1.6.2:
    ....  If the resource
    has no meaningful state at the time that the SUBSCRIBE message is
    processed, this NOTIFY message MAY contain an empty or neutral body
but is difficult for me to interpret what it means.

Example: I ask the presence for a user xyz who registered and quit 
application long time ago:

SUBSCRIBE sip:xyz at ekiga.net SIP/2.0
CSeq: 1 SUBSCRIBE
Via: SIP/2.0/UDP 
82.238.108.175:5060;branch=z9hG4bKdabe824f-1a8e-e011-9efc-0024d693d8e8;rport
User-Agent: Ekiga/3.3.1
From: <sip:eugen.dedu at ekiga.net>;tag=4888824f-1a8e-e011-9efc-0024d693d8e8
Call-ID: f602824f-1a8e-e011-9efc-0024d693d8e8 at snoopy
Supported: eventlist
To: <sip:xyz at ekiga.net>
Accept: application/pidf+xml
Accept: multipart/related
Accept: application/rlmi+xml
Contact: <sip:eugen.dedu at 82.238.108.175:5060>
Allow: 
INVITE,ACK,OPTIONS,BYE,CANCEL,SUBSCRIBE,NOTIFY,REFER,MESSAGE,INFO,PING,PRACK
Expires: 300
Event: presence
Content-Length: 0
Max-Forwards: 70

I receive the following answer:

NOTIFY sip:eugen.dedu at 82.238.108.175:5060 SIP/2.0
CSeq: 1 NOTIFY
Via: SIP/2.0/UDP 86.64.162.35;branch=z9hG4bK2a99.b8a72c47.0
User-Agent: Kamailio (1.5.3-notls (i386/linux))
From: sip:xyz at ekiga.net;tag=f85b0bd16aaafa8479586ac9f88b3198-10a0
Call-ID: f602824f-1a8e-e011-9efc-0024d693d8e8 at snoopy
To: sip:eugen.dedu at ekiga.net;tag=4888824f-1a8e-e011-9efc-0024d693d8e8
Contact: <sip:86.64.162.35:5060>
Subscription-State: active;expires=370
Event: presence
Content-Length: 0
Max-Forwards: 70

To resume: What does SIP standard say about this NOTIFY with empty body? 
  Does this mean that the user xyz is offline?

Or does this mean that user's status has not changed?  In fact, the 
NOTIFY with empty body (as shown above) is the first one sent by 
kamailio, so there is no "previous" state of that user, hence 
"unchanged" status has no meaning.

Thank you,
-- 
Eugen