Subject: [rohc] ROHC 3095:undetected SN LSB wraparounds

From: "Andon Batchvarov" <[email-masked]>
Date: Mon, 16 Oct 2006 17:58:41 +0200

Hi,

While evaluating the context repair algorithm at the decompressor according to RFC 3095 I have discovered the following issue: sometimes the first packet after a prolonged loss (long enough so that a SN LSB wraparound occured) is reconstructed with the wrong SN but this is not detected by the CRC verification (the C is in SO state and the D is in FC state so UO-0 packets with 3-bit CRC are used). The packet is assumed to be correctly decompressed and the value of the last successful decompression as well as the SN reference are (wrongly) updated. When the next packet arrives and a CRC error is detected (because of the wrong reference SN) a wraparound is not assumed because the interval since the last correct decompresion is now very small. The check for a wrong SN update fails as well. As a consequence, the D assumes context damage and moves to the SC state (depending also on the values of k and n).

My question is: was this issue a taken into consideration when designing the RFC? Was it recognized but considered to happen infrequently and thus not covered by the context repair algorithm or has it not been discovered yet? Maybe you can give me a link to a discussion from the past years that I have missed. Thanks!

Best regards,
Andon 
-- 
GMX DSL-Flatrate 0,- Euro* - Überall, wo DSL verfügbar ist!
NEU: Jetzt bis zu 16.000 kBit/s! http://www.gmx.net/de/go/dsl

_______________________________________________
Rohc mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/rohc