[ih] capacity v bandwidth

Sun May 31 19:23:52 PDT 2026

Here is a paper generated by Gemini about this topic.

https://www.dropbox.com/scl/fi/bllks7uio5ikhojavchy5/channel_capacity_paper.pdf?rlkey=2777mhyji3p9d7qenyrpp418j&st=s70py5vb&dl=0

Hesham

On Sun, May 31, 2026, 7:09 PM Brian E Carpenter via Internet-history <
internet-history at elists.isoc.org> wrote:

> Capacity defined as "the number of bits per second which can be
> transmitted by means of the channel" goes back at least to 1961 as a term
> of art, according to Shannon's colleague Pierce. A mathematically rigorous
> definition is in Shannon's 1949 paper but again its unit is bits per second.
>
> I agree that the capacity of a tank is measured in cubic metres and the
> capacity of a computer memory is measured in bits. But pipeline capacity is
> measured in cubic metres per second, or barrels per day. Nobody talks about
> the Strait of Hormuz having a normal bandwidth of 20 million barrels of
> crude per day.
>
> Regards/Ngā mihi
>     Brian Carpenter
>
> On 01-Jun-26 11:55, John Day via Internet-history wrote:
> > Like the capacity of a pipeline?
> >
> >> On May 31, 2026, at 17:45, Jack Haverty via Internet-history <
> internet-history at elists.isoc.org> wrote:
> >>
> >> Getting back to the original capacity<->bandwidth topic...
> >>
> >> I don't think "capacity" is the right terminology either.  Capacity
> usually means how much "stuff" can be held, i.e.:
> >>
> >>
> >>            noun
> >>
> >> 1. The ability to receive, hold, or absorb something.
> >>    the storage capacity of a car's trunk.
> >> 2. The maximum amount that can be contained.
> >>    a bin filled to capacity.
> >>
> >> So it's appropriate to talk about the capacity of a 5TB drive, or 64GB
> of memory in a computer.  But "capacity" says nothing about rate of flow of
> the "stuff" involved, whether it's bits on a wire or gallons of oil in a
> tank car.
> >>
> >> As an industry or science or engineering discipline, it seems to me
> that "networking" has avoided defining and adopting its own terminology for
> important constructs.   Terms like "bits" are generic.  Terms like
> "packets" are borrowed from earlier disciplines.   Pony Express riders
> carried "packets" via horseback:
> >>
> >> "In the context of thePony Express, the mail packet was called
> a*mochila*(Spanish for "backpack" or "pouch"). It was a specialized leather
> saddlebag designed to hold approximately*20 pounds*of mail, with the horse
> carrying an additional*20 pounds*of material."
> >>
> >> Back in the 1980s, I remember discussions using terms such as something
> like "kilobytes per minute per mile".   That reflected the reality of
> transmitting data over distances.  The further you had to move data, the
> harder it was to do and the more it cost to do it.  As far as I remember,
> no one created a term for such metrics.
> >>
> >> Other disciplines have created terminology.  Medical of course has been
> quite prolific.  Same with Law.  Even disciplines such as Electricity has
> unique terminology.  For example, "ampacity" is a term in electrical codes,
> used to define how much current a particular wire can carry.  That dictates
> how much power can be moved through the wire.  A wire has lots of relevant
> parameters that factor into its ampacity.
> >>
> >> Why hasn't our networking industry developed its own terminology...?
> >>
> >> So, I don't know when or why "bandwidth" became common.
> >>
> >> But I do remember the history of another networking term.  In the early
> Internet, the boxes interconnecting networks were called "gateways".
>  Today they're called "routers".  But why the change...?
> >>
> >> In the early/mid 1980s, BBN was selling X.25 networks to all sorts of
> corporations and government users.  Our small sales force would find
> prospects.  Sometimes they asked about this new "Internet" thing, and I got
> called in to explain what it was.  All users were struggling with how to
> integrate their suddenly affordable PCs and workstations.   The Internet
> seemed like a possible solution.
> >>
> >> Our sales force reported back that prospects liked the Internet story,
> but hated the thought of having "gateways" in their IT world.  Other
> companies (e.g., IBM) had products called "gateways", and the users had
> apparently experienced lots of problems with such systems.  The term
> "gateway" was a potent killer of sales.
> >>
> >> So we started callig them "routers".  Other companies (cisco, proteon,
> ...) probably had similar experiences in their sales activities.  Gateways
> faded into historical oblivion, to be replaced by routers - same products,
> but much more palatable to customers.
> >>
> >> What's in a Name?  A lot.
> >>
> >> /Jack Haverty
> >>
> >>
> >>
> >> On 5/31/26 13:57, Brian E Carpenter via Internet-history wrote:
> >>> Unfortunately we failed to correct that terminological error in RFC
> 6214
> >>> (the IPv6 version of RFC 1149), and worse we discussed
> "bandwidth-delay product".
> >>>
> >>> Regards/Ngā mihi
> >>>     Brian Carpenter
> >>>
> >>> On 01-Jun-26 07:53, D Waitzman via Internet-history wrote:
> >>>> In RFC-1149, I wrote "The bandwidth is limited to the leg length."
> >>>>
> >>>> I stand corrected that I should have used "capacity", but then the
> pun would not work.
> >>>> What's more important, the pun or technically accuracy? :-)
> >>>>
> >>>> --
> >>>> David Waitzman
> >>>>
> >>
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