TS encoding in Extension 3

Asked by afathy on 2010-08-30

Do we need to consider the few bits of TS in the base header while encoding TS in extension type 3?

the implementation ignores the preceeding TS bits in the base header in both encoding and decoding, (5 bits for UOR-2 and UOR-2-TS)

I can't find in the RFC 3095 a hint on whether we should devide the TS bits among the base header and the extension header or we just ignore these 5 bits in the base header?

The same question applies to IP-ID (5 bits for UOR-2-ID and UO-1-ID)

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2010-08-30
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2012-03-11
Launchpad Janitor (janitor) said : #1

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

Hello,

I'm very sorry for the long delay before this answer. It seems I simply missed your question at that time...

The TS and IP-ID bits shall be continued across several fields. Padding shall be used if the fields are larger than the size of the value. RFC 3095, ยง4.5.7 says:

    4.5.7. Encoded values across several fields in compressed headers

     When a compressed header has an extension, pieces of an encoded value
     can be present in more than one field. When an encoded value is
     split over several fields in this manner, the more significant bits
     of the value are closer to the beginning of the header. If the
     number of bits available in compressed header fields exceeds the
     number of bits in the value, the most significant field is padded
     with zeroes in its most significant bits.

The TS value is correctly managed in last trunk version. The number of bits to store in extension 3 is computed when the base header is created. Padding is eventually added when needed. See the pieces of code for UOR-2-RTP and UOR-2-TS base headers:
  http://bazaar.launchpad.net/~didier-barvaux/rohc/main/view/head:/src/comp/c_generic.c#L5414
  http://bazaar.launchpad.net/~didier-barvaux/rohc/main/view/head:/src/comp/c_generic.c#L5627
See also the following pieces of code for extension 3:
  http://bazaar.launchpad.net/~didier-barvaux/rohc/main/view/head:/src/comp/c_generic.c#L6656
  http://bazaar.launchpad.net/~didier-barvaux/rohc/main/view/head:/src/comp/c_generic.c#L6754

The IP-ID field is correctly managed in trunk too. It was fixed by ticket https://bugs.launchpad.net/rohc/+bug/761955.

Regards,
Didier

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