Re: [AVTCORE] Comments ondraft-ietf-avtcore-feedback-supression-rtp-07

[Qin Wu <[e-mail]>]

Hi,Magnus:
As regarding if there is better solution, I have some corrections and additional thoughts.
I think 
If the media source is the repair server,
the receiver should set timer to T1=max(the RTT from media source to middlebox sending TPLR, 1/2 of RTT from middlebox to receiver) when the receiver 
receives first TPLR. When the receiver receive addtional TPLR within T1, the receiver should reset the timer to the RTT from media source to middlebox sending TPLR.

If the middlebox is the repair server, the receiver should set the timer to T2=1/2 of RTT from middlebox to receiver when the receiver 
receives first TPLR. When the receiver receive addtional TPLR within T2, the receiver should reset the timer to the T2.

Regards!
-Qin
  ----- Original Message ----- 
  From: Qin Wu 
  To: Magnus Westerlund ; IETF AVTCore WG ; [e-mail] 
  Sent: Tuesday, October 11, 2011 9:40 AM
  Subject: Re: [AVTCORE] Comments ondraft-ietf-avtcore-feedback-supression-rtp-07


  Hi, Magnus,
  Thank for your valuable review, please see my replies belows.

  Regards!
  -Qin
  ----- Original Message ----- 
  From: "Magnus Westerlund" <[e-mail]>
  To: "IETF AVTCore WG" <[e-mail]>; <[e-mail]>
  Sent: Thursday, October 06, 2011 5:37 PM
  Subject: [AVTCORE] Comments on draft-ietf-avtcore-feedback-supression-rtp-07


  Thanks for updating the draft,

  I have reviewed the updated draft and have the following comments on the
  updated version. Some issues are follow up on previous version or on the
  actual changes.

  2. Section 3.
    "The timer value shall be
     based on the observed round-trip time.  A receiver should compute an
     estimate of the round-trip time (RTT) to the sender of TPLR from RTCP
     report round-trip time if available, or its reception time of the
     reflected RTCP FB message (e.g.,NACK), or any other means."

  We hade the discussion before but now that you clarified which RTT to be
  used, I think it is worth having a discussion if that RTT is the right
  one. So you suggest that the RTT between the sender of the TPLR and the
  receiver of the message is the most appropriate to use when suppressing
  the message. I am not certain that is the case.

  Lets consider the use cases. In the case of an intermediary in a
  distribution tree sending the TPLR and at the same time sending a NACK
  upstream. Then the time until the retransmission reaches the suppressed
  receiver is the time from the sending of the NACK up to the
  retransmitting entity and all the way down past the TPLR sender to the
  suppressed receiver. The receiver may not have a true RTT to the
  original media sender as that source appears to live at the TPLR sender,
  not further upstream.

  Yes, the sender of the TPLR and the receiver might at least have mutual
  knowledge of each other, thus the TPLR sender is able to determine the
  lowest RTT in the set of receviers thus determining how often to repeat
  it to cover additional time requried for the upstream part of the
  request. But I do note that these times aren't matching what appear to
  be the delays in the systems.

  Can we find a better solution?