[ih] Question on Flow Control

[Gergely Buday]

Kurose & Ross' networking book covers these very well.

- Gergely

A segunda, 29/12/2025, 16:44, John Day via Internet-history <
internet-history at elists.isoc.org> escreveu:

> ;-) Just quickly, this is what google said:
>
> The Go-Back-N (GBN) protocol wasn't invented at a single moment but
> evolved as an improvement over simpler methods like Stop-and-Wait, gaining
> prominence as a key sliding window technique for reliable data transfer,
> with core concepts solidifying in the late 1970s and 1980s, becoming
> integral to protocols like TCP and widely studied in the 1990s for
> applications like early ADSL, formalizing efficient pipelining for
> networks.
>
> Which if true, is wrong. That would put GBN later than the dynamic window
> in TCP and TS.
>
> (From a practical experience, one has to get to fairly high bandwidth (for
> the time) before stop-and-wait is the best that is possible. Even 512 byte
> message at 56Kbps is over a hundred miles long, if memory serves.)
>
> I will ask Gemini.
>
> > On Dec 29, 2025, at 10:37, vinton cerf <vgcerf at gmail.com> wrote:
> >
> > 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 <mailto: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 <mailto:
> 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>
> <mailto: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
> >> >>
> >> >>
> >> >> --
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> >> >
> >> >
> >> > --
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> >> > Vint Cerf
> >> > Google, LLC
> >> > 1900 Reston Metro Plaza, 16th Floor
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> >> >
> >> >
> >> > until further notice
> >> >
> >> >
> >> >
> >>
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