Dear Mr. Li, dear experts,

thank you very much for your response but the question remains unsettled still.

Your answer is concentrated on the Packet #3. With no doubt this packet is non-critical. Therefore, our questions was about Packet #2 and the protection with ULP #2.

Here is the scenario in doubt again: + However, when considering your example in Figure 1 on the next page, we found + a simple loss situation, for which the above statement does not seem to hold anymore: + Let us assume that out of the seven given packets, exactly (information) packets #2 and #3 + are lost, but all the others have been received correctly. Since packets #1-#3 are only + protected with one single FEC packet, ULP #1, at level L_0, the leftmost part of the + lost packets #2 and #3 can definitely not be recovered anymore.

+ If we now consider the protection strategy for level L_1, we see that the second part of + packets #1, #2, #4, and #5 are protected via the respective part of FEC packet, ULP #2. + But only the part belonging to packet #2 has been lost (packet #3 is not related to ULP + #2), which should definitely be recoverable then. + Thus, we would be able to overcome the loss in packet #2 at protection level L_1, but + not at level L_0, which is a contradiction to the above statement.

The statement about the grouping rules in the document is describing one important general principles for any efficient forward

error correction

scheme. It is nice to know that Mr. Gero agrees on the same principle. We are not intending to claim that the grouping rules in APC-1905 absolutely guarantees the property

Of course we agree on that. It is one of the favourable characteristics of our approach to guarantee the recovery within this rules.

For example, in a interleaving scheme proposed in APC-1841, even correctly

transmitted data will have to be discarded because of the holes in rearranged packets.

In opposition to the UCLA proposal this data are not protected in a special way(normal regressive profile). Within the UCLA proposal the packets are first processed completely and then discarded anyway.

Best Wishes Gero Baese

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