Subject: [rohc] Question on clarity of bit order in RFC 3095

From: Andrew Worsley <[email-masked]>
Date: Wed, 24 Jul 2002 05:36:46 +1000

I would just like to ask if other people think the description of variable
length encoding is unclear.

  I am happy we have the right interpretation from interworking at Interops
but there are two particular aspects which could be clarified, possibly in
the implementor's guide.

On page 34:

  4.5.6.  Self-describing variable-length values

  It talks about the first bit or bits  - perhaps this clarified to be the most
  significant bits. Some of the hardware engineers I have been working with
  think this confusing because different hardware orders their bits
  differently.

  Also it is unclear the precise encoding used for multi-byte values. e.g. is
  0x80 encoded as 0x80 00 or 0x80 80 (the latter is the correct one).
  Obviously this allows 0x80 00 to be used to represent 0x0 as well which is
  a little wasteful. Perhaps they wanted to allow padding?

  Finally I guess it assumes network byte order as this is the only one that
  is workable.

  I guess there must also be a standard some where which defines the byte
  ordering and numbering to be used in all RFCs unless otherwise stated
  (network byte ordering). Does anyone know what this might be?

  	Thanks
		Andrew

Andrew Worsley,
Ericsson AsiaPacificLab, Communications Platforms
Phone: +61 3 9911 2077

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

---

From: [email-masked]
Date: Thu, 25 Jul 2002 00:42:18 +0800 (SGT)

Hi!

My interpretation of RFC 3095 is that all values sent in the ROHC headers 
are in NBO. So there is no confusion in my view.

>   a little wasteful. Perhaps they wanted to allow padding?

The NBO argument applies here too. Yes the point about 0x8000 representing 
0x0 being wasteful is right. It could be designed such that 0x8000 would 
represent 0x80, thus increasing the range that the two octets can 
carry by not overlapping the values. I am wondering about the reasons why 
this approach was not taken (extra cpu cycles?)  

>   (network byte ordering). Does anyone know what this might be?

I would say the understanding is that all values on the wire are in NBO, 
unless otherwise specified.

> Ericsson AsiaPacificLab, Communications Platforms

Regards,
Sukanta

-----------------------------------------------------
Sukanta Kumar Hazra                
R&D Engineer (Networks Division)
Institute for Communications Research
(Formerly the Centre for Wireless Communications)
Tel   : +65 68709338               
Fax   : +65 67795441              
Email : [email-masked]    
-----------------------------------------------------