Subject: [AVT] No_data in the RFC3267

From: [email-masked]
Date: Mon, 19 Sep 2005 16:26:14 +0200

Hello,

I try to understand the exact behavior of an RFC3267 termination when 
no_data frame is detected.   As it is describes in the RFC3267,

"Note that packets containing only NO_DATA frames SHOULD NOT be 
  transmitted.  Also, frame-blocks containing only NO_DATA frames at 
  the end of a packet SHOULD NOT be transmitted, except in the case of 
  interleaving. " 

what is the behavior of the transmitter when there is a packet with 
no_data frame at the beginning of the frame blocks? Is it required to send 
it? 

what is the behavior of the receiver when it receives a packet with a 
no_data frame at the beginning of the frame blocks or a data at the end? 
Is it processed as an error case or is it ignored by the receiver?

Thanks in advance for your help,

Regards,

Yannick STEPHAN

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

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From: Magnus Westerlund <[email-masked]>
Date: Mon, 19 Sep 2005 17:06:26 +0200

Hi,

See inline

> no_data frame at the beginning of the frame blocks? Is it required to send 

Frame-blocks with only NO_DATA frames in them should not be transmitted, 
only in interleaved mode may they be necessary to transmit. However 
there are cases where on may need/benefit from sending all frame types 
including NO_DATA. When one skips NO_DATA in the beginning the TS 
indicates where in the time sequence the first included frame belongs. 
And skipped frames shall be replaced with NO_DATA at the receiving end.

> no_data frame at the beginning of the frame blocks or a data at the end? 

To process it as normal.

> Is it processed as an error case or is it ignored by the receiver?

It is not an error case, the sender has wasted bandwidth, nothing more. 
All received frames should simply be put into the receiver buffer.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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From: [email-masked]
Date: Tue, 20 Sep 2005 10:43:07 +0200

Hi Magnus,

thanks a lot for your answer. 

an additionnal question:

in the RFC3267, when the redundancy is enabled for a codec mode (window = 
1 for example) , what is the sample reference  used to insert the 
timestamp  in the RTP header. Is it the first sample of the first block or 
the first sample of the second one? 
When there is no data, does this timestamp correspond to the single block 
in the packet?

Regards,

Yannick STEPHAN

Magnus Westerlund <[email-masked]>
19/09/2005 17:06
 
        To:     Yannick STEPHAN/FR/ALCATEL@ALCATEL
        cc:     [email-masked]
        Subject:        Re: [AVT] No_data in the RFC3267

Hi,

See inline

To process it as normal.

Cheers

Magnus Westerlund

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From: Magnus Westerlund <[email-masked]>
Date: Tue, 20 Sep 2005 10:49:57 +0200

> When there is no data, does this timestamp correspond to the single block 
The timestamp always referes to the first sample of the first (oldest) 
frame-block (independent of frame type as it can be speech, sid or 
NO_DATA) in the payload. So when using redundancy it will reference the 
oldest of the redundnat frame-blocks included in the payload.

Cheers

Magnus Westerlund

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From: [email-masked]
Date: Tue, 20 Sep 2005 11:14:37 +0200

Magnus,

I've put an example based on my understanding but it is not yet clear in 
my mind for the SN+5 and SN+6 packets. Could you confirm that this figure 
is correct and indicates the timestamp value for the SN+5 and SN+7 
packets? Thanks again for your time.

Regards,

Yannick.

This example is based on a redundancy scheme (window=1). The first column 
is the RTP Sequence Number, the second column is the Timestamp value. The 
field between brackets correspond to the sample reference for the 
timestamp. "nd" is for no data and we consider in this example that 
"no_data" is not transmitted in the packet.
SIDf: SID first
SIDu: SID update

20/09/2005 10:49

Cheers

Magnus Westerlund