Subject: RE: [AVT] RTCP Implementation?

From: [email-masked]
Date: Tue, 26 Mar 2002 13:01:58 +0200

Hi,

my understanding is that you have to implement RTCP, but not use it if you don't need it. For example, using SDP BW modifiers you can set the receiver BW to zero and turn off the receiver reports. Now, since no lip synch is needed on a single voice media flow, probably also SRs can be turned off, in a point-to-point connection.

So, the issue here is: you implement RTCP, but you don't use it. And if you don't use it, you would not need to implement it. Or did I miss anything?

Regards,

Igor Curcio

-----Original Message-----
From: ext Colin Perkins [mailto:[email-masked]]
Sent: Monday, March 25, 2002 9:46 PM
To: Srikrish
Cc: [email-masked]
Subject: Re: [AVT] RTCP Implementation? 

--> "Srikrish" writes:
>Hello,
>
>  I have a question on RTCP implementation.
>  Will appreciate answers/suggestions on this regard.
>
>  Is it common trend to implement RTCP
>  in all RTP implementation?
>
>  In otherwords, if the solution needs
>  only realtime voice and have enough
>  bandwidth, is it mandatory to implement
>  RTCP?

Yes.

Colin

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

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

---

From: Colin Perkins <[email-masked]>
Date: Tue, 26 Mar 2002 10:11:42 -0500

Hi,

Section 6 of draft-ietf-avt-rtp-new-11.txt has a long explanation of why
RTCP "SHOULD be used". I strongly recommend that all implementations use
RTCP, for the reasons described there, and to aid forward compatibility
with more advanced uses of RTP. 

An RTCP implementation is not especially complex, and there is open source
example code which can help (contact me off-list for details).

Colin

--> [email-masked] writes:
>Hi,
>
>my understanding is that you have to implement RTCP, but not use it if you
>don't need it. For example, using SDP BW modifiers you can set the receiver
>BW to zero and turn off the receiver reports. Now, since no lip synch is
>needed on a single voice media flow, probably also SRs can be turned off,
>in a point-to-point connection.
>
>So, the issue here is: you implement RTCP, but you don't use it. And if
>you don't use it, you would not need to implement it. Or did I miss
>anything?
>
>Regards,
>
>Igor Curcio
>
>

---

From: Stephen Casner <[email-masked]>
Date: Tue, 26 Mar 2002 11:06:43 -0800 (PST)

As Colin said, we strongly encourage that all implementations include
RTCP and that it be used.  Part of the original question from Srikrish

>   bandwidth, is it mandatory to implement

How do you know that you have enough bandwidth and that packets are
not being lost?  If you believe that you know the answer today, can
you be sure that it will be the same tomorrow, when someone uses your
implementation in a new way that you did not anticipate?

The revised RTP spec (draft-ietf-avt-rtp-new-11.txt) now includes
Section 10 specifying the requirements for congestion control:

   All transport protocols used on the Internet need to address
   congestion control in some way [29]. RTP is not an exception...
   Since RTP may be used for a wide variety of applications in many
   different contexts, there is no single congestion control mechanism
   that will work for all. Therefore, congestion control SHOULD be
   defined in each RTP profile as appropriate. For some profiles, it may
   be sufficient to include an applicability statement restricting the
   use of that profile to environments where congestion is avoided by
   engineering. For other profiles, specific methods such as data rate
   adaptation based on RTCP feedback may be required.

And the revised RTP A/V profile (draft-ietf-avt-profile-new-12.txt)
says:

        Congestion: RTP and this profile may be used in the context of
             enhanced network service, for example, through Integrated
             Services (RFC 1633) [4] or Differentiated Services (RFC
             2475) [5], or they may be used with best effort service.

             If enhanced service is being used, RTP receivers SHOULD
             monitor packet loss to ensure that the service that was
             requested is actually being delivered. If it is not, then
             they SHOULD assume that they are receiving best-effort
             service and behave accordingly.

             If best-effort service is being used, RTP receivers SHOULD
             monitor packet loss to ensure that the packet loss rate is
             within acceptable parameters. Packet loss is considered
             acceptable if a TCP flow across the same network path and
             experiencing the same network conditions would achieve an
             average throughput, measured on a reasonable timescale,
             that is not less than the RTP flow is achieving. This
             condition can be satisfied by implementing congestion
             control mechanisms to adapt the transmission rate (or the
             number of layers subscribed for a layered multicast
             session), or by arranging for a receiver to leave the
             session if the loss rate is unacceptably high.
             ...

It is important to monitor the loss rate not just for the protection
of the network but also to know whether you are delivering the service
level that you may have promised to your customer.

							-- Steve

---

From: "Srikrish" <[email-masked]>
Date: Tue, 26 Mar 2002 14:54:41 -0800

Hello Steve & Group,

>implementation in a new way that you did not anticipate?

  Your point is valid.
  But the reason I said enough bandwidth available is, the IP network 
  in our situation will be managed IP network (not open internet). 
  And my question is raised from the statement that, RTP need/does 
  not provide QoS or reservation by itself.

  Though I got the point that RTCP is mandatory, I would still like
  to know whether its common in existing VOICE ONLY (realtime) products.

  Thanks for your all your response.

Regards
Srikrish

  
-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Stephen
Casner
Sent: March 26, 2002 11:07 AM
To: Srikrish; [email-masked]
Cc: AVT WG; Colin Perkins
Subject: Re: [AVT] RTCP Implementation?

							-- Steve

---

From: Joerg Ott <[email-masked]>
Date: Wed, 27 Mar 2002 00:12:32 +0100 (MET)

>   to know whether its common in existing VOICE ONLY (realtime) products.

Well, I have half a dozen different IP phones (stand-alone telephone sets --
which I guess qualify as at least kind-of VOICE ONLY) from different vendors
on and around my desks and all of them seem to at least seem to
*send* RTCP properly.

Again, you never know where your equipment will be used or whether
your assumed QoS will be available at all times.  And Internet applications
are supposed to be adaptive.

Joerg