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Subject: Re: [kmip] Feedback on binary alignment proposal
- From: Glen Jaquette <jaquette@us.ibm.com>
- To: kmip@lists.oasis-open.org
- Date: Mon, 27 Apr 2009 18:28:17 -0600
Matt,
I
do see value in revising the TTLV protocol to align it to 4 byte boundaries,
I think we just have to work through the details to make sure we find the
best trade-off. Here are my thoughts:
Your proposal devolves into 2 main ideas
which are essentially separable:
- You observe that the present
composition is essentially a 4 byte Tag followed by a 1 byte Type field
(i.e. (4-byte Tag = 0x42.00.00.YZ)) which immediately throws off
the 4 byte alignment, and this is a first thing that needs to be addressed.
There are various ways to address that:
- The specific proposal you illustrated
on slide 6 is option 1.1 from slide 5 -- namely to drop the leading byte
of the four Tag field, which is 0x42 in all cases today, making it effectively
a 3 byte Tag. Then you transpose the Type and Tag fields, giving:
- (1-byte Type) | (3-byte Tag = 0x00.00.YZ)
- => Pro: this decreases the number
of bytes which need to be communicated to give both Tag and Type by one
- => Con: in response to which a Tony
and Jon observed that this eliminates the 0x42 which has proven useful
in the testing so far
- Someone else (didn't catch the
name) suggested that instead we just pad Tag out to 4 bytes, or effectively:
- (4-byte Tag = 0x42.00.00.YZ) | 4-byte
Type)
- => Pro: this preserves the 0x42.00.00
that can be used to distinguish the start of a new Tag, and hence the start
of a new TTLV message
- => Con: this increases the number
of bytes which need to be communicated to give both Tag and Type by three
- A third option which occurs
to me is a variation of option 1.2 from your slide 5, namely to cut a different
byte from the Tag (0x00 instead of 0x42) and then not transpose
or effectively:
- (4-byte Tag = 0x42.00.YZ) | 1-byte Type)
- => Pro: this decreases the number
of bytes which need to be communicated to give both Tag and Type by one
(i.e. same as 1A)
- => Pro: this preserves the first
two of the distinguishable bytes (i.e. 0x42.00) that can be used to distinguish
the start of a new Tag, and hence the start of a new TTLV message, though
one could argue that is slightly less than the 3 bytes that exist today.
- Similarly make the Value modulo
4 bytes by:
- Padding binary fields out to
the next 4 byte boundary
- Making BIGNUM fields an integer
number of 4 byte fields long
As far as #1 above, I would suggest
we consider 1C. As far as #2, I don't see how to improve on your
proposal.
Regards,
Glen Jaquette
IBM Distinguished
Engineer
(520) 799-2192;
fax: -4138; tieline 321-
Matt Ball <Matthew.Ball@Sun.COM>
Sent by: Matthew.Ball@Sun.COM
04/27/2009 09:26 AM
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| [kmip] Feedback on binary alignment
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Hi Folks,
If you have any preferences regarding the encoding choices from last
Friday's binary alignment presentation, please send them to me by
tomorrow so that I can incorporate them into the first revision of the
proposal. I plan to have the full proposal ready for discussion during
Thursday's meeting, if there is time available on the agenda.
Thanks!
-Matt
View Document Details:
http://www.oasis-open.org/committees/document.php?document_id=32244
Download Document:
http://www.oasis-open.org/committees/download.php/32244/Sun%20KMIP%20Alignment%20Proposal.pdf
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