The measure
Spend alone raises a question. Spend joined to the bandwidth a link delivered, with its role and its contract beside it, answers one: a credit to claim, or a link to resize.
Cost per megabit delivered is a link's monthly recurring cost divided by the bandwidth it actually carried. The arithmetic is plain. What makes it usable is what is printed beside it, starting with the denominator it used.
Two figures share the name and are different facts. Cost per megabit subscribed divides the bill by the rate the contract commits, and needs only the bills. Cost per megabit delivered divides it by what was measured on the link.
The chart at the top of this page sets the two side by side, site by site. The delivered figure is measured from the device over SNMP v3, from the monitoring system you already run, or from the history you upload.
Two denominators, one headline
Each figure names the denominator it used, because an unqualified percentile is the first thing a provider disputes.
| Denominator | Used for |
|---|---|
| DeliveredThe month's p95 over its measured hours, inbound, outbound and both ways | The headline figure |
| SubscribedThe committed rate, from the contract and the bill | The figure from the first bills |
The delivered percentile is named for its hourly bucket. It is a different measure from a provider's burstable figure, taken over shorter samples, and the name keeps the two apart.
The numerator
Recurring charges and discounts, netted, brought to one month, and converted to the group's reporting currency at the rate frozen for that month.1 Each converted amount names the rate it used.
- Usage charges stay out: a run rate that moves with last month's roaming bill is no longer a run rate.
- One-off fees and taxes stay out.
- A charge that cannot be classified is kept and sent to review, so spend is never quietly under-reported.
When the number waits
The delivered figure is worked out only when enough of the month was measured. Where nothing has been reported for a link, its page says so instead of drawing a chart.
When new measurements roll up into a month, its cost per megabit is worked out again. A measured month replaces an uploaded one only once it has observed at least as many hours, and an upload never replaces a month that live monitoring measured.
Units are the other reason. Megabits and kilobits follow the decimal prefixes,2 and some monitoring systems store bytes per second while showing bits: a factor of eight inside the denominator. Riopex converts each unit in one place, under test, so the figure cannot drift by eight.
Coverage travels with the number
Coverage is the share of a month that actually had data, measured against every hour of the month, so a link bound partway through never reads as fully covered.
An hour not measured stays missing, never zero.
- A partly measured hour counts as only part of an hour of coverage.
- A device reboot or counter reset is discarded, never counted as traffic.
- Rebinding an interface never rewrites measured history.
- A waste finding is held back where monitoring is thin, and kept with its reason.
The coverage view lists every link with its source and coverage, and names the links that have gone quiet.
What it is for
Inside the group, it is the fair way to compare companies, sites and providers, because it prices what was delivered rather than what was invoiced. Two companies in two countries hold the same unit.
A link that costs far more per delivered megabit than comparable links across the group opens a finding. The finding carries enough evidence to replay it: the ask to the provider rests on one link, its month and its contract.
The comparison stays inside the group, because pricing-confidentiality clauses make any wider comparison a question of consent.
