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X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 09 Apr 2023 20:06:58 -0000 --------------B7t3FoFHjIMlTalkIJuXpOdy Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Consider a connection to my ISP as being an empty water-pipe, and I only wa= nt to measure the flow from the waterworks to me. In this case the waterwor= ks is Rogers in Toronto, and the numbers come from me measuring the link wi= th the Waveform bufferbloat tool. The ISP promises me 1 Gbit/s of water. OK, there is no such thing, but you= get the idea (;-)) Let's consider the no-latency case. * The ISP turns on the tap, and it takes half an RTT to get to me, one = way. Let that be 1 millisecond, 0.001s of delay. * Once the delay is over, I get (1.0s - 0.001s) * 1 Gbit/s =3D 0.999 Gb= /s. The 0.999 seconds is transfer time, and that transfer is at full speed = of the pipe, so it adds up to 0.999 Gb/s * That's pretty good. Now let's consider the best possible case where there is latency, but only = one delay of 0.456s. That basically means that only one transfer happens i= n the second, so there is only once change for latency to hurt me. * the one-way delay is still 0.001s, but there is also 0.231s of latenc= y, for a delay of 0.232s * (1.0s - (0.001s + 0.231s) ) * 1 Gbit/s =3D * 1.0s - 0.232s =3D 0.549s * 1 Gbit/s =3D 0.768 GB/s * Cut by a quarter, by one packet's delay What about the worst case? * It's not worst, but a pretty common case is a busy link with 1500-byt= e packets * One packet is 12,000 bits * In one second we can transfer 1,000,000,000 bits / 12,000bits/packet = =3D 83,333.3 packets * Maybe that many delays, too? * Fortunately, no I personally observed 456.2 Mbit/s, about 54% of a gigabit at home, so it's= more like the latency cut my bandwidth in half --dave On 4/8/23 22:32, Michael Richardson via Bloat wrote: Dave Collier-Brown wrote: >> Dave Collier-Brown via Bloat wrote: > >> They he said "bandlength" >> >> > That sounded like an odd name, but the idea was cool: >> >> > If I have a bandwidth of 1 Mbit/S, but it takes 2 seconds to deliv= er >> 1 > Mbit, do I have a bandlength of only 1/2 Mbit/S? >> >> Is that because there is 2seconds of delay? > Well, 2 seconds elapsed time, 1 of which is delay. Ah, would that include the delay to ask for the data? (A DNS request, or an HTTP GET) CONFIDENTIALITY NOTICE AND DISCLAIMER : This telecommunication, including a= ny and all attachments, contains confidential information intended only for= the person(s) to whom it is addressed. Any dissemination, distribution, co= pying or disclosure is strictly prohibited and is not a waiver of confident= iality. If you have received this telecommunication in error, please notify= the sender immediately by return electronic mail and delete the message fr= om your inbox and deleted items folders. This telecommunication does not co= nstitute an express or implied agreement to conduct transactions by electro= nic means, nor does it constitute a contract offer, a contract amendment or= an acceptance of a contract offer. Contract terms contained in this teleco= mmunication are subject to legal review and the completion of formal docume= ntation and are not binding until same is confirmed in writing and has been= signed by an authorized signatory. --------------B7t3FoFHjIMlTalkIJuXpOdy Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Consider a connection to my ISP as being an empty water-pipe, and I only= want to measure the flow from the waterworks to me. In this case the water= works is Rogers in Toronto, and the numbers come from me measuring the link= with the Waveform bufferbloat tool.

The ISP promises me 1 Gbit/s of water.  OK, there is no such thing,= but you get the idea (;-))

Let's consider the no-latency case. 

  • The ISP turns on the tap, and it takes half an RTT to get to me, one wa= y.  Let that be 1 millisecond, 0.001s of delay.
  • Once the delay is over, I get (1.0s - 0.001s) = * 1 Gbit/s =3D 0.999 Gb/s. The 0.999 seconds is transfer time, and that transfer is at full speed of the pipe= , so it adds up to 0.999 Gb/s
  • That's pretty good.

Now let's consider the best possible case where there is latency, but on= ly one delay of 0.456s.  That basically means that only one transfer h= appens in the second, so there is only once change for latency to hurt me.

  • the one-way delay is still 0.001s, but there is also 0.231s of latency,= for a delay of 0.232s
  • (1.0s - (0.001s + 0.231s) ) * 1 Gbit/s =3D <= /li>
  • 1.0s - 0.232s =3D 0.549s  * 1 Gbit/s =3D 0.768 GB/s
  • Cu= t by a quarter, by one packet's delay

What about the worst case?

  • It's not worst, but a pretty common case is a busy link with 1500-byte = packets
  • One packet is 12,000 bits
  • In one second we can tran= sfer 1,000,000,000 bits / 12,000bits/packet =3D 83,333.3 packets
  • Ma= ybe that many delays, too?
  • Fortunately, no

I personally observed 456.2 Mbit/s, about 54% of a gigabit at home, so i= t's more like the latency cut my bandwidth in half

--dave


On 4/8/23 22:32, Michael Richardson via Bloa= t wrote:
Dave Collier-Brown <dave.collier-Brown@indexexchange.com>=
; wrote:
    >> Dave Collier-Brown via Bloat<bloat@lists.bufferbloat.ne=
t> wrote: >
    >> They he said "bandlength"
    >>
    >> > That sounded like an odd name, but the idea was cool:
    >>
    >> > If I have a bandwidth of 1 Mbit/S, but it takes 2 seconds=
 to deliver
    >> 1 > Mbit, do I have a bandlength of only 1/2 Mbit/S?
    >>
    >> Is that because there is 2seconds of delay?

    > Well, 2 seconds elapsed time, 1 of which is delay.

Ah, would that include the delay to ask for the data?
(A DNS request, or an HTTP GET)


CONFIDENTIALITY NOTICE AND D= ISCLAIMER : T= his telecommunication, including any and all attachments, contains confiden= tial information intended only for the person(s) to whom it is addressed. Any dissemination, distribution, copying or discl= osure is strictly prohibited and is not a waiver of confidentiality. If you= have received this telecommunication in error, please notify the sender im= mediately by return electronic mail and delete the message from your inbox and deleted items folders. This tel= ecommunication does not constitute an express or implied agreement to condu= ct transactions by electronic means, nor does it constitute a contract offe= r, a contract amendment or an acceptance of a contract offer. Contract terms contained in this telecommunication ar= e subject to legal review and the completion of formal documentation and ar= e not binding until same is confirmed in writing and has been signed by an = authorized signatory.

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