LSB decoding of SN should use shift parameter -1 for IP-only, UDP and UDP-Lite profiles

[Didier Barvaux]

LSB encoding/decoding uses the shift parameter to compute the interpretation interval. The shift parameter, also named p, shall be set to -1 when compressing/decompressing SN for IP-only, non-RTP IP/UDP and non-RTP IP/UDP-Lite profiles.

For non-RTP UDP/IP profile, RFC 3095, §5.11 says:
   The ROHC UDP profile always uses p = -1 when interpreting the SN,
   since there will be no repetitions or reordering of the compressor-
   generated SN. The interpretation interval thus always starts with
   (ref_SN + 1).

For IP-only profile, RFC 3843, §3 says:
   As for ROHC UDP, the compressor generates a 16-bit
   sequence number which increases by one for each packet compressed in
   the packet stream, simply called SN below.

For non-RTP UDP-Lite/IP profile, RFC4019, §5.2 says:
   In particular, the considerations of ROHC UDP regarding the UDP SN
   taking the role of the RTP Sequence Number apply to ROHC UDP-Lite.

The ROHC library uses -1 when encoding, but 0 when decoding.

[Didier Barvaux (didier-barvaux)]

Confirmed on 1.4.x branch.

[Didier Barvaux (didier-barvaux)]

Confirmed on trunk.

[Didier Barvaux (didier-barvaux)]

Fixed in trunk, see http://bazaar.launchpad.net/~didier-barvaux/rohc/main/revision/333.

[Didier Barvaux (didier-barvaux)]

Problem will not be fixed on the 1.4.x branch. Fix for bug #1001435 is required, but missing. A note was added in README about the bug. See http://bazaar.launchpad.net/~didier-barvaux/rohc/1.4.x/revision/337

[Didier Barvaux (didier-barvaux)]

Problem will not be fixed on the 1.3.x branch. Fix for bug #1001435 is required, but missing. A note was added in README about the bug. See http://bazaar.launchpad.net/~didier-barvaux/rohc/1.3.x/revision/192