Arjuna Sathiaseelan wrote:
Dear Tom,
OK, so at least two of us agree that DCCP SHOULD NOT generate DCCP-Data
packets on its own (zero length or otherwise) :-).
:)
So nobody has yet explained why DCCP can't do this for it's own purpose
(although I am not advocating this).
Therefore it seems to me that applications MAY use zero-length packets
as they see fit. The question left is "is RTP an application?" To me,
RTP has many more of the characteristics of a transport protocol than an
application, but it is consistently used over some transport protocol,
so what is it?
I think this has two perspectives:
1) From the RTP's point of view, it has characteristics of a transport
protocol, and infact RTP is a transport protocol for real-time applications.
2)From the underlying transport protocol which carries the RTP packets, RTP
would be considered as an application layer entity?
So, the model I think that Colin has in mind for RTP over DCCP (chime in
if I get it wrong, Colin) is that a real-time application gives data to
RTP, RTP wraps that data in RTP packets and gives that to DCCP, who
wraps the RTP packets in DCCP packets. So from DCCP's point of view,
RTP is the application, and the (real) application has no way of
directly sending DCCP packets. That says that RTP MAY send zero-length
packets.
True. I think so too.
I got all that, until the last sentence, which didn't seem to make any
sense at all. HOW can an application (or upper layer) send zero bytes of
data ... AFAIK, we no interfaces to do this, even if it were sensibel,
which I doubt.
One question that I still have is who is responsible for recognizing
idle and sending something? Is it the RTP stack? Or should the app
send a NOP packet that the RTP stack translates to a zero-length packet?
No!
I am trying to find answers to these questions too. Maybe Colin is the right
person who can shed some light :).
Regards
Arjuna
[snipped]
?
Gorry
