RE: [rohc] P bit role on INPUT-BYTES

Hi Ranjith,

No, the P-bit only affects INPUT-BITS and INPUT-HUFFMAN. There is no re-ordering of bits in the INPUT-BYTES instruction. As I said, RFC 3320 is not perhaps as clear about this as it could be, but there is certainly no intent for input_bit_order to affect INPUT-BYTES.

Cheers,

Mark.

-----Original Message-----
From: Ranjith.V at aricent.com [mailto:Ranjith.V at aricent.com]
Sent: 24 July 2007 14:13
To: West, Mark
Cc: rohc at ietf.org
Subject: RE: [rohc] P bit role on INPUT-BYTES

Hi Mark,

Thank you for your response.

But I have one doubt.

RFC 3320 states
"The P-bit controls the order in which bits are passed from the
dispatcher to the INPUT instructions. If set to 0, it indicates that
the bits within an individual byte are passed to the INPUT
instructions in MSB to LSB order. If it is set to 1, the bits are
passed in LSB to MSB order"

INPUT-BYTES instruction reads byte by byte from Decompressor dispatcher.

Is it means "if P bit is set Decompressor dispatcher provides the byte in the reveres order (LSB to MSB) "

i.e. If P bit is set after reading the byte from DD, UDVM need to reverse the bits in the byte to get the correct value of the byte.

Please comment on this.

Thankyou once again

Thanks and Regards
Ranjith Reddy. V
Extn: 9134
Location : F4-122

"West, Mark" <mark.a.west at roke.co.uk>

07/24/2007 05:47 PM

To	Ranjith Reddy V/BLR/HSS at HSS, <rohc at ietf.org>
cc
Subject	RE: [rohc] P bit role on INPUT-BYTES

Hi Ranjith,

You are correct to say that the P-bit does *not* affect the reading of data in the INPUT-BYTES instruction. INPUT-BYTES always returns only complete bytes, bit-for-bit as found in the input data, irrespective of the P-, F- or H- bits. (The text is not perhaps quite as explicit about this as it could be!)

Cheers,

Mark.

-----Original Message-----
From: Ranjith.V at aricent.com [mailto:Ranjith.V at aricent.com]
Sent: 24 July 2007 11:17
To: rohc at ietf.org
Subject: [rohc] P bit role on INPUT-BYTES

Hi all,

I have a doubt in P-Bit of Input-Bit-Order register :

As per RFC 3320 , section 8.2 :-
"Note that the INPUT-BITS and INPUT-HUFFMAN instructions retrieve a
stream of individual compressed bits from the dispatcher. To provide
bitwise compatibility with various well-known compression algorithms,
the input_bit_order register can modify the order in which individual
bits are passed within a byte."

This points to the fact that P-Bit will not effect Input-Byte
instruction.
The register Input-Bit-Order shall effect only the "Input-Bits" and
"Input-Huffmann" instructions. Please clarify if the value of P-Bit
effect the order of reading bits in byte for INPUT-BYTES instruction.
(Some parts of the same section seems to suggest that P-Bit will
effect the order of bits in all the INPUT instructions.)

Thanks and Regards
Ranjith Reddy. V
Extn: 9134
Location : F4-122

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