Subject: Non-RTP transport in RTSP

From: "Ram Kordale" <[email-masked]>
Date: Fri, 13 Feb 1998 11:32:35 -0800

Does any one why no provision was made to use a non-RTP
data transport. For example, how about plain UDP or ATM/AAL5?
I did not see any discussion on this in the archives (that I had
access to).

Thanks.
Ram

-- 
Ram Kordale

---

From: Anup Rao <[email-masked]>
Date: Fri, 13 Feb 1998 14:29:40 -0800

> data transport. For example, how about plain UDP or ATM/AAL5?

What exactly do you mean when you say  "no provision has been made" ?
The Transport header may any specifier for the type of transport, not
only "RTP/AVP/UDP" or "RTP/AVP/TCP". It is true that nothing else has
been specified *at this point* in the standard, and I am guessing that
is what you mean. 

As far as UDP/IP is concerned, there was a fair bit of discussion on
having something over UDP that was not RTP(Some of this happened at the
San Jose IETF and therefore may not be available in the archives).This
was decided against for the following reasons:-

-RTP is a standard, and does a lot of media-independant things that are
necessary in such an operating environment(such as sequence numbering
and timestamps). The overhead is not really significant.
-RTP,  the associated AVP profile spec. and the SDP spec  specify an
end-end solution ie. codec type, parameters, transport and control.
Plain UDP does not.

If you have a need for such a thing as plain UDP(where the data packets
themselves are  descriptive enough for lossy environments), then you
have 2 options :
-Go ahead use it with a transport identifier such as POUDP(plain ol
udp). ie.
Transport: POUDP/POUDP/UDP or such.
-Use it as above, but pursue standardization and public acceptance as
well.

No one expressed an immediate need for AAL5/ATM as far as I can
remember. The protocol is very extensible in this regard - adding a new
transport type is simple, I would say that choosing the transport type
is  one of the main things RTSP does. I guess you still have the above
two options, with the second being preferable. 

-Anup.