[ih] Question on Flow Control

[vinton cerf]

not sure - try gemini?
v


On Mon, Dec 29, 2025 at 10:35 AM John Day via Internet-history <
internet-history at elists.isoc.org> wrote:

> Yes, it appeared to come later. Or at least I thought so.
>
> Does Go-Back-N require sequence numbers?  I guess not. Just go back
> N-messages.
>
> Do we know when GBN appeared?
>
> John
>
> > On Dec 29, 2025, at 10:29, Vint Cerf <vint at google.com> wrote:
> >
> > John,
> > there is another term "go-back-N" which sounds like a fixed window and
> is a form of ARQ.
> > would the terminology uncover any earlier schemes?
> >
> > v
> >
> >
> > On Mon, Dec 29, 2025 at 9:59 AM John Day via Internet-history <
> internet-history at elists.isoc.org <mailto:internet-history at elists.isoc.org>>
> wrote:
> >> As we all know, there are two forms of sliding window flow control:
> >> 1) the static window, where an Ack causes the window to be moved and
> requires two extra commands, and
> >> 2) the dynamic window, with a credit field that is added to the Ack
> value to find the Right Window Edge (RWE) and doesn’t need the two extra
> commands.
> >>
> >> Static window is found in datacomm protocols such as SDLC, HDLC, and
> variations on them.  (HDLC was created from SDLC.)
> >> Dynamic window is found in most Transport protocols such as TCP, TS,
> TP4, SCTP, QUIC, etc.
> >>
> >> Most textbooks present these as a progression from a simple
> stop-and-wait protocol with increasing complexity through static window to
> dynamic window as if this was the order of development. That dynamic
> winsdow was an enhancement of static window.
> >>
> >> However, that does not seem to be borne out by the historical record,
> but it isn’t clear. This is what I have been able to determine:
> >> 1) Static window is in SDLC, an integral part of IBM’s SNA.
> >>
> >> 2) SNA was released in 1974 with SDLC.
> >>
> >> 3) I have not been able to find anyone (or any paper) who knows about
> the development inside IBM of SDLC, nor was SDLC based on precursors either
> inside or outside IBM.
> >>
> >> 4) I have not been able to find anything about a sliding window flow
> control protocol prior to 72 or 73.
> >>
> >> 5) Dynamic window first appeared in CYCLADES TS in late 1972 or early
> 73 and was incorporated into the early drafts of Sept 73.
> >>
> >> That doesn’t give much time for overlap and IBM in this period kept
> their cards pretty close to their chest.
> >>
> >> So the questions are:
> >>
> >> 1) Did fixed window originate at IBM with SDLC?
> >>
> >> 2) Was there an earlier fixed window precursor to SDLC that was inside
> or outside IBM?
> >>
> >> 3)  Was there an external fixed window precursor that was the example
> for both?
> >>
> >> 4)  Is this a case of independent invention?  Were static and dynamic
> window flow control invented independently?
> >>
> >> It isn’t an earth-shattering question, but it is curious and does seem
> to run counter to the typical exposition in textbooks.
> >>
> >> Take care,
> >> John Day
> >>
> >>
> >> --
> >> Internet-history mailing list
> >> Internet-history at elists.isoc.org <mailto:
> Internet-history at elists.isoc.org>
> >> https://elists.isoc.org/mailman/listinfo/internet-history
> >> -
> >> Unsubscribe:
> https://app.smartsheet.com/b/form/9b6ef0621638436ab0a9b23cb0668b0b?The%20list%20to%20be%20unsubscribed%20from=Internet-history
> >
> >
> >
> > --
> > Please send any postal/overnight deliveries to:
> > Vint Cerf
> > Google, LLC
> > 1900 Reston Metro Plaza, 16th Floor
> > Reston, VA 20190
> > +1 (571) 213 1346
> >
> >
> > until further notice
> >
> >
> >
>
> --
> Internet-history mailing list
> Internet-history at elists.isoc.org
> https://elists.isoc.org/mailman/listinfo/internet-history
> -
> Unsubscribe:
> https://app.smartsheet.com/b/form/9b6ef0621638436ab0a9b23cb0668b0b?The%20list%20to%20be%20unsubscribed%20from=Internet-history
>