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Re: [tsvwg] Comments on draft-ietf-tsvwg-udp-options-02

Joe Touch <touch@strayalpha.com> Thu, 24 May 2018 18:33 UTC

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Date: Thu, 24 May 2018 11:33:34 -0700
From: Joe Touch <touch@strayalpha.com>
To: "C. M. Heard" <heard@pobox.com>
Cc: Tom Jones <tom@erg.abdn.ac.uk>, tsvwg <tsvwg@ietf.org>
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Subject: Re: [tsvwg] Comments on draft-ietf-tsvwg-udp-options-02
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On 2018-05-24 11:09, C. M. Heard wrote:

> ...
> So we do need to deal with LIE data lengths from 0 through 3.

Agreed, but I don't think it needs to change what's in the existing doc
all that much. 

For 4 or more, do what's in the doc. 

For 0-3, then "slide" the LITE option before the LITE data, e.g.: 

the lite header = [L I T E] 
lite data = caps, e.g., U V W X Y Z or a subset thereof 
other options = a b c d e ... 

before transmitting: 
        lite data len:    lite area and options: 
       ------------------------------------------ 
              0 bytes     [L I T E] a b c d e ... 
              1 byte      U [L I T E] a b c d e ... 

              2 bytes     U V [L I T E] a b c d e ... 

              3 bytes     U V W [L I T E] a b c d e ... 

              4 bytes     U V W X [L I T E] a b c d e ...  
              5 bytes     U V W X Y [L I T E] a b c d e ...  
              6 bytes     U V W X Y Z [L I T E] a b c d e ... 

after transmitting 
              0 bytes     [L I T E] a b c d e ... 

              1 byte      [L I T E] U a b c d e ... 

              2 bytes     [L I T E] U V a b c d e ... 

              3 bytes     [L I T E] U V W a b c d e ... 

              4 bytes     [L I T E] U V W X a b c d e ...
              5 bytes     [L I T E] Y U V W X a b c d e ...  
                                    ^ 
              6 bytes     [L I T E] Y Z U V W X a b c d e ... 
                                    ^ ^ 

The issue is highlighted with the carets (^).  

For 3 bytes or less, "SLIDE" 
For 4 bytes, SLIDE is the same as SWAP 
For more than 4 bytes, SWAP is more efficient than SLIDE (avoids a long
copy of the data) 

I don't think it's bad to have a special case for 3 or fewer bytes. 

Joe

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