Most of these are generated from the same modules the site’s own tools run on, so the picture and the arithmetic behind it cannot disagree. Each one says underneath where its numbers came from and, where they came from somebody else, the date the page was read.
To reuse one: credit Inbound CX and link to this page. That is the whole licence. The French version of every diagram sits at the same file name with .fr before the extension.
How a call travels
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<a href="https://inboundcx.com/diagrams#anatomy-of-a-voip-call"><img src="https://inboundcx.com/blog/figures/anatomy-of-a-voip-call.svg" alt="Why a call can connect and still have no sound" width="760" height="332"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#anatomy-of-a-voip-call">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#the-cheap-codec-is-not-eight-times-cheaper"><img src="https://inboundcx.com/blog/figures/the-cheap-codec-is-not-eight-times-cheaper.svg" alt="Published codec bit rate against the real bandwidth of one call on Ethernet. The names promise a ratio of 8.0 to 1 between G.711 and G.729 (8 Kbps); on the wire the ratio is 2.8 to 1." width="760" height="434"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#the-cheap-codec-is-not-eight-times-cheaper">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#call-quality-what-150-ms-means"><img src="https://inboundcx.com/blog/figures/call-quality-what-150-ms-means.svg" alt="The three one-way delay bands of ITU-T Recommendation G.114, from transparent to unacceptable." width="760" height="285"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#call-quality-what-150-ms-means">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#g711-why-eight-bits-sound-like-twelve"><img src="https://inboundcx.com/blog/figures/g711-why-eight-bits-sound-like-twelve.svg" alt="Transfer curve of G.711 mu-law against uniform 8-bit coding. G.711 spends 29 of its 128 values on the quietest one percent of the range and 1 on the loudest one percent." width="760" height="447"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#g711-why-eight-bits-sound-like-twelve">Inbound CX</a>, CC BY 4.0.</p>
Phone numbers
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<a href="https://inboundcx.com/diagrams#anatomy-of-a-north-american-number"><img src="https://inboundcx.com/blog/figures/anatomy-of-a-north-american-number.svg" alt="What each part of a number decides" width="760" height="317"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#anatomy-of-a-north-american-number">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#split-or-overlay"><img src="https://inboundcx.com/blog/figures/split-or-overlay.svg" alt="Split or overlay: the two ways to add numbers" width="760" height="327"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#split-or-overlay">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#quebec-area-code-families"><img src="https://inboundcx.com/blog/figures/quebec-area-code-families.svg" alt="Quebec's four area code families" width="760" height="329"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#quebec-area-code-families">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#what-moves-when-you-port-a-number"><img src="https://inboundcx.com/blog/figures/what-moves-when-you-port-a-number.svg" alt="What follows the number, and what stays behind" width="760" height="329"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#what-moves-when-you-port-a-number">Inbound CX</a>, CC BY 4.0.</p>
The market
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<a href="https://inboundcx.com/diagrams#what-a-phone-line-means-now"><img src="https://inboundcx.com/blog/figures/what-a-phone-line-means-now.svg" alt="Composition of the 473 million retail voice connections in the United States as of 2025-06-30: 15 million switched access lines, 63 million VoIP subscriptions and 395 million mobile subscriptions." width="760" height="279"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#what-a-phone-line-means-now">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#ucaas-ccaas-cpaas"><img src="https://inboundcx.com/blog/figures/ucaas-ccaas-cpaas.svg" alt="UCaaS, CCaaS, CPaaS: which one you are actually shopping for" width="760" height="297"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#ucaas-ccaas-cpaas">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#the-seat-price-ladder"><img src="https://inboundcx.com/blog/figures/the-seat-price-ladder.svg" alt="Lowest published price per seat per month at eight vendors, from 15 to 119 US dollars." width="760" height="402"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#the-seat-price-ladder">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#what-the-market-does-not-publish"><img src="https://inboundcx.com/blog/figures/what-the-market-does-not-publish.svg" alt="Four questions put to 8 competing vendors. None publishes a spending ceiling, included minutes, call-transfer capabilities, or Quebec's privacy law." width="760" height="408"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#what-the-market-does-not-publish">Inbound CX</a>, CC BY 4.0.</p>
What it costs, and what it counts
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<a href="https://inboundcx.com/diagrams#seat-user-or-concurrent"><img src="https://inboundcx.com/blog/figures/seat-user-or-concurrent.svg" alt="Seat, user, or concurrent call: what you are actually buying" width="760" height="374"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#seat-user-or-concurrent">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#the-list-and-the-calls"><img src="https://inboundcx.com/blog/figures/the-list-and-the-calls.svg" alt="Three quantities of different kinds: 258.5 million Do Not Call registrations, 3.9 billion robocalls in a single month, and 2.6 million complaints in the year." width="760" height="289"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#the-list-and-the-calls">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#what-every-phone-system-asks-of-audio"><img src="https://inboundcx.com/blog/figures/what-every-phone-system-asks-of-audio.svg" alt="What every phone system asks of an audio file" width="760" height="377"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#what-every-phone-system-asks-of-audio">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#how-many-lines-not-people"><img src="https://inboundcx.com/blog/figures/how-many-lines-not-people.svg" alt="Simultaneous channels needed to keep blocking at or under 1 per cent, by load. One erlang needs 5; four erlangs need 10." width="760" height="428"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#how-many-lines-not-people">Inbound CX</a>, CC BY 4.0.</p>
Running a phone line
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<a href="https://inboundcx.com/diagrams#the-five-metrics"><img src="https://inboundcx.com/blog/figures/the-five-metrics.svg" alt="The five metrics, and what one more person does to them" width="760" height="374"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#the-five-metrics">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#why-small-teams-cannot-run-hot"><img src="https://inboundcx.com/blog/figures/why-small-teams-cannot-run-hot.svg" alt="Curve of occupancy against call volume at a constant service level. At low volume 3 people run at 36 per cent occupancy; at high volume 56 people run at 89 per cent." width="760" height="448"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#why-small-teams-cannot-run-hot">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#what-the-average-wait-hides"><img src="https://inboundcx.com/blog/figures/what-the-average-wait-hides.svg" alt="Comparison of average speed of answer against the wait actually borne by callers who queue. At 14 people the average is 10 seconds while those who wait hold for 60 seconds." width="760" height="433"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#what-the-average-wait-hides">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#the-peak-half-hour-sizes-the-team"><img src="https://inboundcx.com/blog/figures/the-peak-half-hour-sizes-the-team.svg" alt="People who must be free in each half hour of an example day. The peak is 20 at 09:30 and the mean is 14.4." width="760" height="428"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#the-peak-half-hour-sizes-the-team">Inbound CX</a>, CC BY 4.0.</p>
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<a href="https://inboundcx.com/diagrams#how-long-before-they-press-zero"><img src="https://inboundcx.com/blog/figures/how-long-before-they-press-zero.svg" alt="Two greetings measured against the 20 second threshold. The second runs about 27 seconds before the first option." width="760" height="279"></a> <p>Figure: <a href="https://inboundcx.com/diagrams#how-long-before-they-press-zero">Inbound CX</a>, CC BY 4.0.</p>
The tools behind some of these
Several of the diagrams are drawn by the same code that runs the free tools, where you can put your own numbers in instead of ours.
See the free tools