Subject: [AVT] RTCP question

From: "Mistler, Art" <[email-masked]>
Date: Tue, 4 Sep 2001 11:48:47 -0400

Hello All,

I'm working on integrating RTP into a media server.  And the engineering
team continues to flip-flop on opinions as to whether RTCP is really a
mandatory requirement for the solution.  We will not be using IP
multicast in the product, but realize that it is still recommended for
all environments. (Section 6 of RFC1889, just after the 4 function
descriptions for RTCP)

People here have received private comments, from customer feedback and
engineering peers, that RTCP is not such a stringent requirement, and
that it is highly dependent on the actual real time media that is being
transferred.  I was wondering if anyone had any recommendations how I
might get closer to an answer.  For instance, what types of application
areas most definitely need RTCP and what types of application areas can
benefit from it, but live without it.

Regards,
- RT

RT Mistler
ThinkEngine Networks, Inc.
175 Maple Street
Marlboro, MA  01752
(508) 597-0464
mailto:[email-masked]
The Network Listens, Understands and Responds

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
http://www1.ietf.org/mailman/listinfo/avt

---

From: Marshall Eubanks <[email-masked]>
Date: Tue, 04 Sep 2001 12:23:02 -0400

> Hello All,

Well, as it says in
http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-new-10.txt

   Functions 1-3 SHOULD be used in all environments, but particularly in
   the IP multicast environment. RTP application designers SHOULD avoid
   mechanisms that can only work in unicast mode and will not scale to
   larger numbers. Transmission of RTCP MAY be controlled separately for
   senders and receivers, as described in Section 6.2, for cases such as
   unidirectional links where feedback from receivers is not possible.

If you are doing one to many multicast, IMHO you absolutely should handle SR
and produce RR at the receiver. This is the ONLY way, in most cases, to get
a handle on network performance. Of course, RTCP is really necessary for any
many to many multicasting

Depending on the application, using the time sync functionality of RTCP
may be necessary as well.

RTCP is really not that hard to implement, I would urge you to do so.
 
                                 Regards
                                 Marshall Eubanks

> ThinkEngine Networks, Inc.

T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624            Fax     : 703-293-9609
e-mail : [email-masked]

 Test your network for multicast : http://www.multicasttech.com/mt/
 Check the status of multicast in real time :
 http://www.multicasttech.com/status/index.html

---

From: Colin Perkins <[email-masked]>
Date: Tue, 04 Sep 2001 12:44:45 -0400

RTCP is necessary for lip-sync, and useful for other purposes (e.g. you may
be interested in the reception quality feedback). I would strongly urge you
to implement it.

Colin

---

From: "Brian Hagar" <[email-masked]>
Date: Tue, 04 Sep 2001 10:07:22 -0700

Colin,

My understand from previous discussions on this mailing list is that it is
mandatory to implement but not mandatory to send except for multi-cast
environments.

Brian

---

From: Colin Perkins <[email-masked]>
Date: Tue, 04 Sep 2001 14:14:07 -0400

Correct. My note was intended to clarify that you need to send RTCP if
you're intending to do lip-sync, and may want to send it in order to
get recepetion quality feedback.

Colin

---

From: Ping Pan <[email-masked]>
Date: Tue, 04 Sep 2001 12:21:49 -0700

Just trying to be a devil's advocate for a moment:

A while ago, someone was telling me the reason why not implementing RTCP
in their "box": rtp encapsulation is very simple to be done at data
forwarding level (given all the coding information, etc. are fixed).
RTCP is a different matter. It must be done by the control processor.
Now, each RTP session must be closely tracked, and per-session data
information must be collected accurately. To support a large number of
RTP sessions, some timer tricks are needed as well... The question is:
if the guy does not want to support multicast, does not care about fast
timeout and does not want to see the QoS feedback, is there any reason
to implement RTCP?

Thanks!

- Ping

---

From: Colin Perkins <[email-masked]>
Date: Tue, 04 Sep 2001 15:50:26 -0400

>timeout and does not want to see the QoS feedback, is there any reason

Yes, if he wants to synchronise multiple streams.

Colin