RE: [AVT] ULP FEC question

["Adam Li" <adamli@icsl.ucla.edu>]

Hi Christine,

In the example in section 8.3 of that draft (p.17), the protection is
done in the following in that particular case.

ULP packet #1 protects Packet A, B for the first L0 bytes.

ULP packet #2 protects Packet C, D for the first L0 bytes, 
and Packet A, B, C, and D for the following L1 bytes.

So to answer your question, the ULP level 1 for ULP packet #2 performs
on the last two packets (C and D). 

If the protection grouping is applied according to the very simple rules
(particularly rule <c>) described in Section 5.3, then the ULP packets
always start with Level 0. In other words, the ULP packets can only be 

(1) Level 0;
(2) Level 0 + level 1;
(3) Level 0 + level 1 + level 2;
(4) etc.

This is also illustrated in the samples in the following sections.

Hope it helps. If there are any more questions, please let me know. I
would be happy to clarify and help.

Adam

-----Original Message-----
From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On Behalf Of Xtine
Pepin
Sent: Friday, October 11, 2002 12:56 PM
To: avt@ietf.org
Subject: [AVT] ULP FEC question

Hello,
 
I am new to the mailing list and currently working on improving the
robustness of VoIP applications to packet losses.
I would have a question regarding the draft entitled "An RTP payload
format for generic FEC with uneven level protection". 
I don't really see how UEP is achieved in the third example with 2
protection levels (p. 17). Is ULP level 1 (for ULP packet #2) performed
on all 4 packets or simply the last two? Are you automatically
generating a new ULP packet for every protection level? 
 
Thank you all in advance!
 
-Christine Pepin

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