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

[Joe Touch <[e-mail]>]

On 2018-05-25 09:01, C. M. Heard wrote:

> Hi Joe, 
> 
> Regarding this: 
> 
> On Thu, May 24, 2018 at 11:39 AM, Joe Touch <[e-mail]> wrote:
> 
> On 2018-05-06 10:23, C. M. Heard wrote: 
> Section 8, UDP options vs. UDP-Lite: Is the following paragraph left over from a previous incarnation of the draft? 
> 
> UDP options support a similar service to UDP-Lite by terminating the
> UDP options with an EOL option. The additional data not covered by
> the UDP checksum follows that EOL option, and is passed to the user
> separately. The difference is that UDP-Lite provides the un-
> checksummed user data to the application by default, whereas UDP
> options can provide the same capability only for endpoints that are
> negotiated in advance (i.e., by default, UDP options would silently
> discard this non-checksummed data). Additionally, in UDP-Lite the
> checksummed and non-checksummed payload components are adjacent,
> whereas in UDP options they are separated by the option area -
> which, minimally, must consist of at least one EOL option.
> 
> It seems to me that this should be rewritten, because the service in question is now provided by the LITE option. 
> 
> This text is exactly explaining the difference between our LITE and "UDP-Lite". I can clarify this, e.g.,: 
> The UDP option LITE option supports a similar service to UDP-Lite.... 
> Is there some part of this explanation of the differences that isn't accurate?

  The trouble with the above explanation (a) that is starts with an
inaccurate description of how the LITE option works -- the unchecksummed
data does NOT follow EOL in the surplus area 

Yes, that was from previous text and needs to be fixed.  

> -- and (b) it says that the checksummed and unchecksummed payload components are separated by the options -- which is not the case; the order, after processing the LITE option (slide/swap), is:
> 
> UDP Header | checksummed payload data | unchecksummed payload data | options |  trailing data following EOL

Agreed - I do also need to check the how FRAG and LITE interact to make
sure this describes the details correctly, but yes - thanks. I didn't
see what you had issue with. 

> I've highlighted the specific sentences that I think have issues, and I propose the following replacement paragraph:
> 
> UDP options, via the LITE option, support a service similar to
> UDP-Lite.  The main difference is that UDP-Lite supports carriage
> of non-checksummed user data between the endpoints by default,
> whereas UDP options can safely provide that service only between
> endpoints that negotiate that capability in advance -- an endpoint
> 
> that does not implement UDP options will silently discard the
> 
> non-checksummed user data, along with the UDP options themselves.
> 
> Hope this helps.

Yes, thanks, 

Joe 

> Mike Heard