I think in that case it's just ensuring the MTU given to the customer
via their access link can be carried through their network without, or
which a minimum of, fragmentation.
I finally found some text to which I was referred, in 3GPP TS 29.060
(GTP) v15.2.0 section 13.2:
All backbone links should have MTU values that exceeds the sum of
the maximum value plus the size of the tunnel headers (IP header, UDP
and GTP header) in order to avoid fragmentation in the backbone.
In this case the "fit for purpose" is clearly delineated as "carrying
GTP traffic".
I'll have to think about better text that "fit for purpose". Can we
say that network operators who can characterize effectively the MTU
requirements of traffic traversing their network should factor in
whatever overhead their operational model requires so as to minimize,
or preferably eliminate, the need for fragmentation.
Operators that can't characterize the MTU requirements of their
customer traffic can decide if they're going to try or not, or care or
not. :-)
On Tue, 13 Nov 2018 at 12:35, Ron Bonica <[email protected]> wrote:
>
> Hi Erik,
>
> Could you refine the recommendation a little bit? If an ISP were to ask,
> "What MTU is fit for my purpose?", how would we answer?
>
> Ron
>
>
> > Ron,
> >
> > Related to this section, at the mic I was suggesting perhaps including some
> > simple text recommending that network operators SHOULD take efforts to
> > make sure the MTU(s) on their network(s) are "fit for purpose", i.e. sized
> > to
> > avoid fragmentation to the extent possible.
> >
> > I'm not sure yet how to better express that notion. It seems obvious and
> > anodyne, but it can be useful to have these things captured for reference by
> > non-IETF documents.
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