Re: [tsvwg] Alternative version of the UDP FRAG option

[Joe Touch <[e-mail]>]

> On Mar 16, 2019, at 11:37 AM, Tom Herbert <[e-mail]> wrote:
> 
> 
> 
>> On Sat, Mar 16, 2019, 11:21 AM Joe Touch <[e-mail]> wrote:
>> 
>> 
>>> On Mar 16, 2019, at 9:06 AM, Tom Herbert <[e-mail]> wrote:
>>> Hi Mike,
>>> 
>>> Thinking about this, it occurs to me be that the LITE option isn't
>>> needed.
>> 
>> AFAICT, there is no LITE option the way you have been trying to evolve it. 
>> 
>>> The assumption in the UDP options draft is that a receiver
>>> needs the UDP payload to immediately follow the UDP header, but the
>>> UDP payload can be anywhere in the surplus area as long as it's
>>> aligned to four bytes. A receiver will know how to handle it and
>>> deliver the UDP data to the application (e.g. by maintaining a pointer
>>> to the data).
>>> 
>>> So that allows a format like:
>>> 
>>> UDP header (Length=8) | Surplus area header | Options | Payload
>> 
>> That’s DOA for legacy receivers.
> 
> 
> Legacy receivers see a UDP datagram with zero payload, just like LITE.

I misunderstood payload to also include cases where Len > 8. Fair enough.
> 
>> 
>> It also basically kills zero-copy.
> 
> 
> Exactly how does it do that?

Zero copy UDP would need to I’ve the lite payload after it has already been placed in memory. That’s not true for the current approach (it was a design goal, in fact, to allow it).

Joe