Hi, Tom,
On 10/9/2016 3:05 AM, t.petch wrote:
> ----- Original Message -----
> From: "Joe Touch" <to...@isi.edu>
> Sent: Saturday, October 08, 2016 12:24 AM
>
>
>> Hi, Tom,
>>
>> Thanks for pointing that out. I'll try to revise to make that easier.
>>
>> If you have any other specific examples, please let me know (either
>> on-list or directly).
> Joe
>
> How about
>
> ' o Tunnel internal MTU (TIMTU): the largest message that a tunnel
> egress can emit into a tunnel without requiring further
> fragmentation to reach the tunnel egress.' ?
>
> You may have to read it twice to see my confusion.
Yes - that's a typo that should read as follows, which should be more clear:
o Tunnel internal MTU (TIMTU): the largest message that a tunnel
ingress can emit into a tunnel without requiring further
fragmentation to reach the tunnel egress.
> More generally, I think that Fred's point is well made, that the
> terminology, particularly the abbreviations thereof - e.g. LMTU, TIMTU,
> TMTU, PMTU, ERMTU, RMTU - make the I-D harder to follow.
The challenge is that it's nearly impossible to discuss these issues
without coining new terms because the existing ones are so poorly
understood in the context of layering.
We generally care about many different MTUs:
- the largest IP packet that can traverse an IP path
this is NOT the path MTU, but rather the receiver reassembly MTU
we CANNOT transmit transport segments larger than the payload of
this IP E2E MTU
- the largest IP packet that can traverse an IP path without needing
on-path fragmentation
this is the path MTU
it is critical for IP source fragmentation (or the packets won't
get there at all)
it's an optimization for transports that frag/reassemble (to
avoid source fragmentation)
Neither of these has anything to do with the link MTU, which has similar
variants.
As we keep discussing this issue, we've come up with various notions of
what these names could be.
We could call these the:
IP transit MTU (defined as the source-to-dest MTU, but equal to the
IP receiver reassembly MTU)
IP path MTU (min of the IP hop MTUs)
IP hop MTU = link/tunnel transit MTU - link/tunnel overhead
link (or tunnel) transit MTU (defined as source-to-dest MTU, equal
to link/tunnel receiver reassembly MTU)
link path MTU (min of the link hop MTUs)
link hop MTU = MTU of a single physical link
I'm glad to revise if these are more clear.
Joe
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